Tropical blackwater biogeochemistry: The Siak River in...

Tropical blackwater biogeochemistry: The Siak River in Central Sumatra, Indonesia

Dissertation

zur Erlangung des Doktorgrades

der Naturwissenschaften (Dr. rer. nat.)

vorgelegt von

Antje Baum

Bremen 2008

Advisory Committee:

1. Reviewer: Dr. Tim Rixen

Center for Tropical Marine Ecology (ZMT), Bremen, Germany

2. Reviewer: Prof. Dr. Wolfgang Balzer

University of Bremen

1. Examiner: Prof. Dr. Venugopalan Ittekkot


2. Examiner: Dr. Daniela Unger


I

Contents

Summary .................................................................................................................... III

Zusammenfassung...................................................................................................VII

1. Introduction........................................................................................................ 11

2. Published and submitted papers..................................................................... 15

2.1. Sources of dissolved inorganic nutrients in the peat-draining river Siak,

Central Sumatra, Indonesia ................................................................................... 15

2.2. The Siak, a tropical black water river in central Sumatra on the verge of

anoxia ..................................................................................................................... 31

2.3. Relevance of peat draining rivers in central Sumatra for riverine input of

dissolved organic carbon into the ocean ................................................................ 55

2.4. DOC discharges from the Indonesian blackwater river Siak and its estuary

into the Malacca Strait and their role as DOC source for the Indian Ocean .......... 69

3. General conclusions ......................................................................................... 83

4. Future perspectives .......................................................................................... 85

5. References ......................................................................................................... 87

Appendix ................................................................................................................... 99

III

Summary

The most studied tropical blackwater rivers are tributaries of the Orinoco and

Amazon such as the Rio Negro in South America. The dark-brown colour of

blackwater rivers results from high concentrations of dissolved organic matter that is

leached from organic-rich soils within the river drainage basins. The catchment areas

of the blackwater rivers in South America are mainly covered by mineral soils

(ferralsols), which feature high contents of organic matter in the upper soil horizons.

Blackwater rivers in South East Asia by contrast drain catchments that are dominated

by organic soils (dystric histosols), commonly referred to as tropical peat.

Approximately 83% of the South East Asian peatsoils are located in Indonesia,

mainly on the islands Sumatra, Borneo and Irian Jaya and hold ~3% of the global

carbon stored in soils. During the last few decades, deforestation and drainage of

peat swamp forests have become common land-use practices in Indonesia mainly for

the establishment of oil palm estates resulting in the dissolution of Indonesian

peatsoils and enhanced CO2-emissons.

The main objectives of this work were to investigate potential environmental impacts

of land-use changes on the peat-draining Siak River (Central Sumatra) and to assess

the role of Indonesian rivers as source of dissolved organic carbon (DOC) into the

ocean.

This work was carried out within the framework of the Indonesian/German

cooperation SPICE (Science for the Protection of Indonesian Coastal Marine

Ecosystems) and included four expeditions to the Siak River.

Collected samples were analysed for dissolved inorganic nutrients, DOC, oxygen and

amino acids (Appendix). In addition particulate carbon and nitrogen as well as their

isotopic compositions were determined in river, soil and terrestrial plant samples

(Appendix). DOC decomposition experiments were carried out and annual freshwater

discharges of the Siak were determined by in situ measurements as well as by

evaluation of precipitation and evaporation data. Based on geographical information

IV Summary

systems (GIS) a digital terrain model was established to provide essential

hydrological information on the river catchment.

The low nutrient concentrations measured in the Siak relative to other rivers not only

in Indonesia but world-wide may be attributed to leaching of nutrient-poor peatlands.

Nevertheless, there are clear indications that nutrient concentrations in the vicinity of

cities, villages and industrial sites were considerably enhanced. Furthermore,

washout of fertilizers could be observed during one of the expeditions. Nutrient data

measured in a peat-draining river in South Sumatra, which was sampled prior to the

main cultivation of oil palms in the 1970s, revealed nutrient concentrations which are

much lower than those measured in the Siak. This suggests that nutrient

concentrations in the Siak doubled during the last few decades as observed also in

other rivers world-wide.

Contrary to the nutrient concentrations DOC in the Siak and its tributaries was mainly

derived from leaching of the surrounding peatsoils. Due to massive land-use changes

leaching could not be considered as natural. Although leaching is assumed to be

enhanced the anthropogenic impact is not quantified yet. However, the

concentrations that were measured in this study are among the highest riverine DOC

concentrations reported so far. The highest concentrations were observed after dry

seasons when increasing precipitation rates led to enhanced leaching from soils.

The decomposition of DOC was the main factor influencing the oxygen

concentrations in the Siak. According to model results an increase in the DOC

concentrations of ~15% would be sufficient to produce anoxic conditions in the Siak.

The average annual river discharge of the Siak into the river estuary was calculated

to be 0.38 ± 0.1 Tg C yr-1 (Tg = 1012 g) where additional DOC inputs into the Siak

Estuary derived from peatsoil leaching resulted in an overall discharge of the Siak

into the coastal ocean of 0.5 ± 0.3 Tg C yr-1. The DOC discharge of the Siak and

other peat-draining rivers increased the DOC concentration in the Malacca Strait by

approximately 130 μmol L-1, which resulted in a terrestrial DOC discharge of the

Malacca Strait into the Indian Ocean of ~6.4 Tg C yr-1. Therewith ~33% of the

Indonesian DOC discharge which has been extrapolated to be ~21 Tg C yr-1 seems

Summary V

to be exported via the Malacca Strait into the ocean. This demonstrates that the

numerous small Indonesian rivers are as important as the Amazon with respect to

the input of terrestrial-derived DOC into the ocean.

VII

Zusammenfassung

Der wohl bekannteste tropische Schwarzwasserfluss ist der Rio Negro, einer der

größten Nebenflüsse des Amazonas in Südamerika. Zusammen mit weiteren

Nebenflüssen des Amazonas und Orinocos (Südamerika) gehört er zu den am

intensivsten untersuchten Schwarzwasserflüssen weltweit. Schwarzwasserflüsse

entwässern Einzugsgebiete, deren Böden einen hohen Anteil an organischem

Material aufweisen, dessen Auswaschung wiederum zur dunkel-braunen Färbung

des Flusswassers führt. Die Flusseinzugsgebiete der südamerikanischen Flüsse

Amazonas und Orinoco sind zu großen Teilen von mineralischen Böden

(Ferralsolen) dominiert, deren Oberböden häufig einen hohen Anteil an organischer

Substanz aufweisen. In Süd-Ost-Asien hingegen entwässern Schwarzwasserflüsse

hauptsächlich Einzugsgebiete mit einem sehr hohen Anteil an organischen

Torfböden, die als dystrische Histosole klassifiziert werden. Etwa 83% der Torfböden

Süd-Ost-Asiens liegen auf den indonesischen Inseln Sumatra, Borneo und Irian Jaya

und speichern etwa 3% des weltweit in Böden gebundenen Kohlenstoffs. Im Zuge

der Errichtung von Ölpalmplantagen hat die Abholzung von Torfwäldern und

Entwässerung von Torfböden in Indonesien in den vergangenen Jahrzehnten

drastisch zugenommen. Ein verstärkter Abbau dieser organischen Böden und eine

damit einhergehende Erhöhung von CO2-Emissionen sind die Folgen.

Es war daher Ziel dieser Arbeit, mögliche Auswirkungen der Landnutzungs-

veränderungen auf den Fluss Siak (Zentral-Sumatra), dessen Einzugsgebiet einen

hohen Anteil solcher Torfböden aufweist und zudem stark anthropogen geprägt ist,

zu untersuchen. Ferner sollte die Bedeutung indonesischer Flüsse als Quelle von

gelöstem organischen Kohlenstoff (DOC) für den marinen DOC-Pool bewertet

werden.

Die vorliegende Arbeit wurde im Rahmen des indonesisch-deutschen Projektes

SPICE (Science for the Protection of Indonesian Coastal Marine Ecosystems)

erstellt. Im Zeitraum von 2004 bis 2006 wurden vier Expeditionen zur Beprobung des

Siak durchgeführt.

VIII Zusammenfassung

Die im Rahmen der Ausfahrten genommenen Proben wurden auf gelöste

anorganische Nährstoffe, DOC, Sauerstoff und Aminosäuren analysiert (Appendix).

Des Weiteren wurden Kohlenstoff- und Stickstoffkonzentrationen sowie deren stabile

Isotope von suspendiertem Flussmaterial, Boden- und Pflanzenproben bestimmt

(Appendix). Zudem wurden Experimente zum Abbau von DOC im Fluss

durchgeführt. Der jährliche Frischwasserabfluss des Siak wurde durch In-situ-

Messungen bestimmt und mittels der Auswertung von Niederschlags- und

Verdunstungsdaten validiert. Mit Hilfe geographischer Informationssysteme (GIS)

wurde ein digitales Geländemodell erstellt, aus dem wichtige hydrologische

Kenndaten des Flusseinzugsgebietes abgeleitet werden konnten.

Die Nährstoffkonzentrationen im Siak sind sowohl im Vergleich mit anderen Flüssen

Indonesiens als auch weltweit betrachtet gering, was auf die Auswaschung aus den

nährstoffarmen Torfböden im Flusseinzugsgebiet zurückzuführen ist. In der Nähe

von Städten und Industriestandorten wurden jedoch anthropogen erhöhte

Nährstoffkonzentrationen festgestellt. Die Auswaschung von Stickstoffdünger hatte

während einer Expedition zu einem zusätzlichen Eintrag an Nährstoffen in den Siak

geführt. Im Vergleich zu Nährstoffkonzentrationen eines im Süden Sumatras

gelegenen Schwarzwasserfluss aus den 1970er Jahren, sind die im Siak ermittelten

Werte deutlich erhöht. Es ist daher anzunehmen, dass die Nährstoffkonzentrationen

infolge der Intensivierung der Landnutzung in den Flusseinzugsgebieten deutlich

angestiegen sind, was wiederum auch bereits in anderen Flüssen nicht nur in den

Tropen beobachtet worden ist.

Im Gegensatz zu den Nährstoffen wurde der im Siak gemessene DOC hauptsächlich

aus den Torfböden im Flusseinzugsgebiet ausgewaschen. Die Auswaschung aus

den Böden ist aufgrund der starken anthropogenen Nutzung der Torfböden jedoch

längst kein rein natürlicher Prozess mehr. Zwar ist eine anthropogene Verstärkung

der Auswaschung anzunehmen, eine Quantifizierung dieser war jedoch bislang noch

nicht möglich. Im weltweiten Vergleich zählen die ermittelten DOC-Konzentrationen

im Siak zu den am höchsten gemessenen Konzentrationen überhaupt. Die höchsten

DOC-Konzentrationen wurden am Ende von Trockenzeiten beobachtet, wo es

aufgrund ansteigender Niederschlagsraten zu einer erhöhten Auswaschung der

Torfböden gekommen war.

Zusammenfassung IX

Der Abbau des DOC im Siak scheint maßgeblich bestimmend für die

Sauerstoffkonzentration im Fluss. Basierend auf Modellrechnungen würde bereits

eine Zunahme der DOC-Konzentration von ~15% zu ausgeprägten anoxischen

Zonen führen.

Jährlich werden 0,38 ± 0,1 Tg (Tg = 1012 g) DOC ins Ästuar des Siak transportiert.

Die zusätzliche Auswaschung von DOC aus Torfböden im Einzugsgebiet des

Ästuars erhöht den jährlichen Export in den Küstenozean auf 0,5 ± 0,3 Tg C pro

Jahr. Der eingetragene DOC des Siak sowie weiterer in den Küstenozean

mündender Schwarzwasserflüsse führt zu einem Anstieg der DOC-Konzentration in

der Malacca Straße um ~130 μmol L-1. Multipliziert mit dem Frischwassereintrag

exportiert die Malacca Straße demnach jährlich etwa 6,4 Tg terrestrischen DOC in

den Indischen Ozean. Somit werden etwa 33% der DOC-Fracht Indonesiens, die auf

Basis des DOC Exports des Siak auf ca. 21 Tg C pro Jahr abgeschätzt wurde, über

die Malacca Straße in den Indischen Ozean transportiert. Damit ist der DOC-Eintrag

aller Flüsse Indonesiens in den Ozean in etwa mit der DOC-Fracht des Amazonas

gleichzusetzen.

11

1. Introduction

The most famous and intensive studied blackwater rivers in the tropics are tributaries

of the large South American rivers Orinoco and Amazon such as the Rio Negro

which is the largest blackwater river worldwide (Ertel et al., 1986; Richey et al., 1990;

Hedges et al., 1994; Battin, 1998; Hedges et al., 2000). The dark-brown river colour

is caused by humic substances which are leached from organic rich soils located in

the river catchments. South American blackwater rivers drain mainly mineral soils

(ferralsols) with high contents of organic matter in the upper soil horizons. These

strongly weathered soils are widespread in the tropical regions of South America and

Africa (Fig. 1).

Fig. 1: Global distribution of Ferralsols (red areas) and Histosols (green areas) according to (FAO/UNESCO, 2003)

In addition to these soils, South East Asia shows also large areas covered by dystric

histosols, which according to the FAO are also considered as peatsoils and consist

largely of decomposed trees. The organic matter content exceeds 50% in the upper

80 cm and pH values are <5.5 (FAO/UNESCO, 2003).

Approximately 83% of the SE Asian peatsoils (2-3.3 * 105 km2) are located in

Indonesia, mainly on the islands Irian Jaya, Borneo and Sumatra (Rieley et al.,

1996a). With a peat layer thickness of up to 40 m and 26-50 Gt C, Indonesian peat

12 Introduction

soils present a vast reservoir of organic carbon and store approximately 3% of the

global carbon stored in soils (Post et al., 1982; Rieley et al., 1996a; Rieley et al.,

1996b; Rieley and Setiadi, 1997; Page et al., 1999; Page et al., 2002; Hooijer et al.,

2006).

Fig. 2: Indonesian peat soil coverage (Data source: FAO/UNESCO, 2003)

In contrast to South America, Indonesia has no major rivers as it consists of

numerous small volcanic and coral islands. Thus, Indonesian peatsoils are drained

by various small lowland rivers which contribute ~11% (135,000 m3s-1) to the global

freshwater export and therefore are comparable to the Amazon accounting for ~15%

(183,000 m3s-1) (Richey et al., 1991; Syvitski et al., 2005).

During the last few decades Indonesian peatlands have been heavily affected by

slash-and-burn agriculture, commercial logging and particularly the development of

plantations (Ichikawa, 2007) (Fig. 3). According to current estimates approximately

45% of the Indonesian peatlands have already been converted into oil palm

plantations (Hooijer et al., 2006). As a consequence peatsoils turned into CO2

sources with emissions that are more than 4 times higher than Indonesian CO2

emissions caused by the burning of fossil fuels, cement production and gas flaring

(103 Tg C yr-1 in 2004)(Hooijer et al., 2006; Marland et al., 2007).

Introduction 13

Fig. 3: Slash-and-burn agriculture in the catchment of the S. Tapung Kiri (a), drainage activities in the Mandau catchment (b).

Within this context the major objectives of this study were to investigate potential

environmental impacts associated with the massive land-use changes in Indonesia

on the peat-draining river Siak in Central Sumatra and to assess the relevance of

Indonesian rivers for the contribution of terrestrial DOC to the marine DOC pool,

which with ~700 Gt (Gt = 1015 g) holds almost as much carbon as the atmosphere

(~815 Gt C) (Kurz, 1993; Hansell, 2002; Tans, 2008).

a) b)

Published and submitted papers 15

2. Published and submitted papers

2.1. Sources of dissolved inorganic nutrients in the peat-draining river Siak,

Central Sumatra, Indonesia

Antje Bauma, Tim Rixena, Gerd Liebezeitb, Ralf Wöstmannb, Christine Josec, Joko

Samiajic

aCenter for Tropical Marine Ecology, Fahrenheitstrasse 6, 28359 Bremen, Germany

bResearch Centre Terramare, Schleusenstrasse 1, 26382 Wilhelmshaven, Germany

cUniversity of Riau, Jl. Simpang Panam Km 12.5, Pekanbaru, Riau, Indonesia

Biogeochemistry, submitted 3 June 2008

Abstract Dissolved inorganic nutrients (NO3

-, NO2-, NH4

+, PO43-) of the peat-draining Siak

River in Central Sumatra were determined during four campaigns between 2004 and

2006. Concentrations of dissolved inorganic nitrogen (DIN) varied between 5.8 and

65.1 μmol L-1. Enhanced DIN concentrations associated with high proportions of

NH4+ indicated increased wastewater discharges in the populated areas of the

drainage basin. The highest DIN concentrations were observed in March 2004 where

nitrogen-fertilization of oil palm plantations was followed by heavy rainfall which

resulted in enhanced leaching. Although locally water hyacinths act as nitrogen sink

nutrient uptake by freshwater plankton in general seems to play a minor role in the

Siak due to light limiting conditions. Overall the phosphate (PO43-) concentrations

varied between 0.2 and 17.7 μmol L-1 with occasional concentration peaks of up to

197 μmol L-1 near industrial areas, reflecting anthropogenic origin. Increased

leaching as a result of anthropogenic activities and wastewater discharges could

have doubled the DIN concentrations in the Siak as suggested by comparison of the

Siak data with those of a peat-draining river in South Sumatra measured in the

1970s.

Keywords: leaching, nutrients, Sumatra (Indonesia), peat, wastewater

16 Published and submitted papers

Introduction Estuaries and coastal oceans represent the land-sea interface where interactions

between continents, atmosphere and open ocean take place (Mantoura et al., 1991).

Increases in human activities in river catchments have led to major changes of river

discharges (Vollenweider, 1992; Carpenter et al., 1998; Van Drecht et al., 2003;

Billen and Garnier, 2007). As a result of agricultural, industrial, domestic wastewater

discharges as well as soil leaching caused by land-use changes over the last few

decades, riverine nutrient deliveries by rivers into the coastal ocean have increased

by a factor of 1.5 to 2 (Meybeck, 1982; Vollenweider, 1992; Rabouille et al., 2001;

Bouwman et al., 2005; Dumont et al., 2005).

Slash-and-burn agriculture, commercial logging and the development of plantations

have led to an enormous forest loss in South East Asia (Ichikawa, 2007). In

Indonesia, where ~83% of the SE Asian peatsoils are located, the area of peatlands

converted into timber and mostly oil palm plantations nearly tripled between 1985 to

1998 (Page and Rieley, 1998; Hooijer et al., 2006; Murdiyarso and Adiningsih, 2007).

This present study aims at the investigation of processes controlling nutrient

dynamics in the peat-draining river Siak in Central Sumatra.

Study area With a length of ~370 km and a catchment area of ~11.500 km2 the Siak is one of the

major rivers draining the Central Sumatran lowlands. It originates at the confluence of

the two headstreams S. Tapung Kanan and S. Tapung Kiri. The S. Tapung Kanan

and the major tributary Mandau rise in the peat-dominated lowlands while the S.

Tapung Kiri originates at the foot of the Central Sumatran Mountains (Fig. 1). The

monthly rainfall in the Siak catchment ranges between 101 and 398 mm resulting in a

mean annual freshwater discharge of ~370 m3s-1 (Fig. 2) (GPCC, 2005; Baum et al.,

2007). Approximately 45% of the Siak catchment is covered by tropical peatsoils; the

vegetation is dominated by lowland forests and shrubs as well as by oil palm and

rubber plantations (Laumonier, 1997).


Fig. 1: Study area showing the Siak River located in Central Sumatra. Sampling stations of the different campaigns in March 2004, September 2004, July/August 2005 and March 2006 are marked with light grey, dark grey, white and black circles, respectively. Peat areas are coloured in green.

The Siak is located in the province of Riau and flows directly past the capital

Pekanbaru (100° 26’ E; 0° 32’ N, river km 180), which is with a population of 680000

inhabitants the largest city of the province. Two smaller industrial cities, Perawang

(river km 220) and Siaksriindrapura (river km 286) are also directly located at the

Siak subjecting the Siak to high loads of domestic sewage and untreated discharges

from sawmills, oil, paper and rubber processing plants.


Fig. 2: Monthly mean precipitation rates for 2004-2006 derived from the Global Precipitation Climatology Center (GPCC) for the province of Riau (0° to 2° N). Black bars mark the precipitation rates during the four campaigns in March and September 2004, July 2005 and March 2006.

Methods Sampling and sample preparation

Dissolved inorganic nutrients, total suspended matter (TSM) and dissolved organic

carbon (DOC) were sampled in March and September 2004, July/August 2005 and

March 2006 (Fig. 1). In 2004 and 2005 the entire Siak system including the

headstreams S. Tapung Kanan and S. Tapung Kiri as well as the Mandau were

investigated while in 2006 the study was focussed on the Siak mainstream and the

lower reaches of both headstreams. The coastal ocean was sampled in 2005 and

2006 (Fig. 1).

Water samples for nutrient analyses were obtained from a water depth of ~1 m with a

1L Niskin bottle, filtered through 0.45 μm syringe-filters, fixed with HgCl2 and stored

cool until analysis. Samples for DOC were filtered, acidified with phosphoric acid and

stored cool until analysis.


TSM was collected by filtering water through pre-combusted glass-fibre-filters

(Whatmann GF/F). The filters were dried at 40° C and analysed for particulate

organic carbon (POC), particulate organic nitrogen (PON) as well as stable carbon

(�13C) and nitrogen isotopes (�15N).

Plant samples (leaves) were collected along the river banks of the Siak and its

tributaries during the expedition in July/August 2005. Plant samples were dried at

40°C, homogenised and analysed for POC, PON, �13C and �15N.

Analyses

Dissolved inorganic nutrients and dissolved oxygen

Dissolved inorganic nutrients (NO3-, NO2

-, NH4+, PO4

3-) were analysed

spectrophotometrically using a continuous flow autoanalyser (Skalar-SAN-plus).

Dissolved oxygen concentrations were determined by Winkler titration using the

method described by Grasshoff et al. (1999).

Particulate organic carbon and nitrogen (POC and PON)

POC and PON analyses were carried out with a Carlo Erba NA 2100 element

analyser by high temperature combustion. Prior to the analysis of POC GF/F filters

containing total suspended matter (TSM) were acidified with 1N HCl to remove

inorganic carbon and dried at 40° C.

Stable carbon (�13C) and nitrogen isotopes (�15N)

Carbon and nitrogen isotopic compositions were determined in a Finnigan Delta Plus

gas isotope ratio mass spectrometer following high temperature combustion in a

Flash 1112 EA elemental analyser. Carbonate was removed prior to the combustion

from the samples as described above for POC. �13C and �15N values are reported in

‰ relative to PDB standard and N2 in atmospheric air, respectively.

Dissolved organic carbon (DOC)

DOC was analysed by means of high temperature catalytic oxidation using a

Dohrman DC-190 Total Organic Carbon Analyser equipped with a platinum catalyst.

Before injection into the furnace, the acidified samples were decarbonated by purging

with oxygen. The evolving CO2 was purified, dried and detected by a non-dispersive


infrared detection system. Calibration was carried out using potassium phthalate

dissolved in MilliQ water.

Results and Discussion Dissolved inorganic nitrogen (DIN)

DIN concentrations displayed low variations between September 2004, July/August

2005 and March 2006 as indicated by the error bars shown in Fig. 3a while

concentrations measured during the expedition in March 2004 were twice as high

(Fig. 3a). Nonetheless, the trend of DIN concentrations was similar during all

expeditions showing enhanced concentrations in the lower reaches of the S. Tapung

Kiri (river km 0 to 155) and the densely populated zone between Pekanbaru and

Perawang (river km ~180-230) (Fig. 3a). Lower DIN concentrations were measured

at the confluence of the headstreams S. Tapung Kiri and S. Tapung Kanan (river km

~155) and in the Siak Estuary (river km ~325-370). Since the S. Tapung Kiri and the

S. Tapung Kanan revealed mean DIN concentrations of 36.1 and 32.0 μmol L-1,

respectively (Tab. 1), mixing of the two water masses cannot explain the observed

decrease in DIN at the S. Tapung Kiri and the S. Tapung Kanan junction.

Nutrient uptake by freshwater plankton is generally assumed to be an important DIN

sink in rivers. However, the dark-brown water of the Siak reduces the light

penetration to depths of < 20 cm which limits photosynthesis and subsequent growth

of plankton (Baum et al., 2007). Furthermore, the POC concentrations with a mean

value of 176 μmol L-1 are lower compared to other major rivers (Ludwig et al., 1996).

However, a pronounced concentration peak occurred in the Siak Estuary close to a

channel which was cut through peatlands to improve the local infrastructure by

connecting the Siak and the Siak Kecil (Fig. 1, 4).


Fig. 3: A) DIN concentrations along the S. Tapung Kiri (km 0-155) and Siak (km 155-370) in March (circles) and September 2004, July/August 2005 and March 2006 (dots) averaged every 20 km. DIN concentrations of S. Tapung Kanan and Mandau rivers in March 2004 are marked as open squares and in September 2004, July/August 2005 and March 2006 as filled squares. B) Mean contribution of NH4

+ to DIN. The contributions of NH4+ to DIN of all samplings (March and

September 2004, August 2005 and March 2006) are averaged every 20 km along the S. Tapung Kiri (km 0-155) and Siak (km 155-370). C) PO4

3- concentrations along the S. Tapung Kiri (km 0-155) and Siak (km 155-370) in March and September 2004, July/August 2005 and March 2006 (black circles) averaged every 20 km. PO4

3- concentrations of S. Tapung Kanan and Mandau rivers are marked with black squares. PO4

3- peaks in September 2004 are marked as black triangles.

Fig. 4: POC concentrations along the S. Tapung Kiri (km 0-155) and Siak (km 155-370) in March (dots) and September 2004 (white circles), July/August 2005 (grey circles) and March 2006 (black triangles) as well as the C/N ratios for all sampling campaigns (dotted line).

C/N ratios of POM in the Siak ranged between 10 and 21 with the most ratios >14

(Tab. 2), which is higher than those of plankton (C/N 6-7) but similar to ratios of

higher plant derived organic matter (Hedges et al., 1997; Middleburg and Herman,

2007) indicating a terrestrial origin of the POM in the Siak. This is supported by

stable carbon (� 13C) and nitrogen (� 15N) isotopic ratios of POM samples collected in


the river which reveal wider � 13C and � 15N ranges than peat samples and overlap

with those of leaves (Fig. 5).

Fig. 5: Ranges of �13C, �15N and C/N ratios of peat (n=6), leaves (n=28) and POM samples (n=30) taken in the Siak River and its catchment in March and September 2004, July/August 2005 and March 2006.

24

Pub

lishe

d an

d su

bmitt

ed p

aper

s

Tab.

1: M

inim

um, m

axim

um a

nd m

ean

conc

entr

atio

ns o

f nitr

ate

(NO

3- ), ni

trite

(NO

2- ), am

mon

ium

(NH

4+ ) and

pho

spha

te (P

O43-

) of t

he S

. Tap

ung

Kiri

, th

e Si

ak m

ains

trea

m, t

he S

. Tap

ung

Kan

an a

nd th

e tr

ibut

ary

Man

dau

durin

g th

e fo

ur c

ampa

igns

in M

arch

and

Sep

tem

ber 2

004,

Jul

y/A

ugus

t 200

5

and

Mar

ch 2

006.

NO

3- [μm

ol L

-1]

NO

2- [μm

ol L

-1]

NH

4+ [μm

ol L

-1]

PO43-

[μm

ol L

-1]

DIN

[μm

ol L

-1]

R

iver

M

in.

Max

. A

vera

ge

Min

. M

ax.

Ave

rage

M

in.

Max

. A

vera

ge

Min

. M

ax.

Ave

rage

M

in.

Max

. A

vera

ge

Mar

ch 2

004

S. T

apun

g K

iri

38.8

8 53

.41

46.1

5 0.

24

0.56

0.

40

5.69

10

.00

7.85

0.

55

4.34

2.

45

49.1

3 59

.66

54.3

9

Si

ak

25.6

9 57

.18

46.8

2 0.

06

0.45

0.

25

4.73

14

.90

7.86

0.

26

9.28

1.

72

31.5

3 65

.12

54.9

3

S.

Tap

ung

Kan

an

16.8

1 35

.18

26.0

0 0.

03

0.15

0.

09

4.86

8.

41

6.64

1.

04

5.24

3.

14

25.2

4 40

.19

32.7

2

M

anda

u 2.

57

3.84

3.

21

0.00

0.

00

0.00

3.

26

4.22

3.

74

0.57

0.

87

0.72

5.

83

8.06

6.

94

Sept

embe

r 200

4 S.

Tap

ung

Kiri

23

.51

23.5

1 23

.51

1.28

1.

28

1.28

2.

37

2.37

2.

37

1.26

1.

26

1.26

27

.16

27.1

6 27

.16

Si

ak

6.00

36

.76

21.9

9 0.

00

12.1

9 1.

61

0.00

15

.83

3.76

1.

18

197.

43

32.2

6 7.

89

37.2

4 27

.36

S.

Tap

ung

Kan

an

55.5

8 55

.58

55.5

8 0.

02

0.02

0.

02

7.22

7.

22

7.22

2.

13

2.13

2.

13

62.8

2 62

.82

62.8

2

M

anda

u 24

.10

24.1

0 24

.10

0.22

0.

22

0.22

3.

75

3.75

3.

75

15.3

9 15

.39

15.3

9 28

.06

28.0

6 28

.06

July

/Aug

ust 2

005

S. T

apun

g K

iri

22.4

2 44

.89

34.0

6 0.

06

0.25

0.

17

1.15

2.

64

2.05

0.

98

4.42

2.

72

24.4

2 46

.22

36.2

7

Si

ak

9.02

37

.10

20.6

9 0.

03

0.37

0.

18

0.37

9.

73

4.13

0.

00

5.26

1.

66

11.5

1 46

.91

25.3

5

S.

Tap

ung

Kan

an

21.1

4 41

.41

31.3

7 0.

02

0.23

0.

10

3.52

12

.77

5.39

1.

14

3.72

2.

84

24.8

7 53

.94

36.8

6

M

anda

u 3.

02

8.47

5.

75

0.06

0.

51

0.20

1.

69

2.92

2.

37

1.45

13

.89

4.75

5.

87

11.4

5 8.

99

Mar

ch 2

006

S. T

apun

g K

iri

9.56

9.

71

9.64

0.

12

0.20

0.

16

0.29

0.

29

0.29

0.

67

3.54

2.

10

10.0

4 10

.11

10.0

8

Si

ak

8.62

31

.15

21.7

8 0.

05

1.09

0.

44

0.56

12

.46

3.15

0.

23

3.78

1.

20

9.32

38

.98

25.3

7

S.

Tap

ung

Kan

an

9.12

12

.51

10.8

1 0.

03

0.09

0.

06

1.19

1.

40

1.30

15

.83

17.7

0 16

.76

10.6

1 13

.73

12.1

7

M

anda

u n.

d.

n.d.

n.

d.

n.d.

n.

d.

n.d.

n.

d.

n.d.

n.

d.

n.d.

n.

d.

n.d.

n.

d.

n.d.

n.

d.


Therefore it is assumed that POM in the Siak originates largely from leaves of the

riparian vegetation, except for the sites that exhibited pronounced POM peaks. Here

lighter �15N (mean 1.3 ‰) and slight increases in �13C values (mean -29 ‰) are

indicative of enhanced input of peat-derived organic matter most likely as a result of

peat-erosion along the channel banks. However, lower POM concentrations which

are mainly of terrestrial origin in combination with light limiting conditions suggest that

the role of primary producers in the consumption of nutrients in the Siak as well as in

its estuary is not significant. Thus, decreasing DIN concentrations with increasing

salinities suggest that dilution of river water with nutrient-poor ocean water is the

main factor reducing the DIN concentrations in the Siak Estuary.

Water hyacinths (Eichhornia crassipes) which are known for their high nutrient

removal (Reddy and D'Angelo, 1990) were abundant especially at the S. Tapung Kiri

and S. Tapung Kanan junction. Accordingly, it is assumed that DIN uptake by the

water hyacinths could have decreased the DIN concentrations at this site.

Nitrate (NO3-) contributed up to 85 % to DIN in the Siak except at the Mandau

junction and within the densely populated and industrialised area between

Pekanbaru and Perawang (Fig. 3b). In the Mandau, up to 59 % of DIN consisted of

NH4+. The Mandau is a classic blackwater river with low oxygen (0.8 to 3.2 mg L-1,

mean = 1.7 mg L-1) and high DOC contents, which results from leaching of the

adjacent peatsoils covering up to 48 % of its catchment (Baum et al., 2007). In such

environments the lack of oxygen reduces nitrification (Reddy and D'Angelo, 1994;

Kieckbusch and Schrautzer, 2007). This could explain the high proportion of NH4+ in

the Mandau and in the Siak at the Mandau junction (river km ~245) (Fig. 3b). The

other site at which NH4+ contributed significantly to DIN (up to ~23 %) was the

densely populated and industrialised area between Pekanbaru and Perawang (Fig.

3b). Compared to the Mandau oxygen contents were slightly higher (1 to 3.7 mg L-1,

mean = 2.6 mg L-1) in this area. In wastewater channels that discharge directly into

the Siak, DIN concentrations were extremely high (~565-1,877 μmol L-1) (Tab. 3) and

NH4+ contributed 63-96 % to DIN. Thus, the increased percentage in NH4

+ of the total

DIN and the overall enhanced DIN concentrations were most likely the result of

wastewater inputs in the area between Pekanbaru and Perawang (Fig. 3a, b).

26

Pub

lishe

d an

d su

bmitt

ed p

aper

s

Tab.

2:

Min

imum

, m

axim

um a

nd m

ean

conc

entr

atio

ns o

f pa

rtic

ulat

e or

gani

c ca

rbon

(PO

C),

C/N

rat

ios

and

stab

le c

arbo

n (�

13C

) an

d ni

trog

en

isot

opes

(�15

N)

of t

he S

. Ta

pung

Kiri

, th

e Si

ak m

ains

trea

m (

with

out

estu

ary)

, th

e S.

Tap

ung

Kan

an a

nd t

he t

ribut

ary

Man

dau

durin

g th

e fo

ur

cam

paig

ns in

Mar

ch a

nd S

epte

mbe

r 200

4, J

uly/

Aug

ust 2

005

and

Mar

ch 2

006.

POC

[μm

ol L

-1]

C/N

�13

C [‰

] �15

N [‰

]

R

iver

M

in.

Max

. A

vera

ge

Min

. M

ax.

Ave

rage

M

in.

Max

. A

vera

ge

Min

. M

ax.

Ave

rage

Mar

ch 2

004

S. T

apun

g K

iri

123.

23

129.

95

126.

59

13.5

516

.44

14.9

9 -2

8.79

-2

8.35

-2

8.57

4.

42

7.16

5.

79

Si

ak

84.4

5 35

0.68

15

6.59

10

.14

17.4

014

.28

-29.

00

-28.

29

-28.

65

3.02

6.

61

4.60

S.

Tap

ung

Kan

an

104.

59

118.

12

111.

36

15.1

818

.34

16.7

6 -2

9.34

-2

9.05

-2

9.19

4.

00

4.94

4.

47

M

anda

u 10

8.58

10

8.58

10

8.58

15

.28

15.2

815

.28

-29.

66

-29.

33

-29.

49

2.87

8.

62

5.74

Sept

embe

r 200

4 S.

Tap

ung

Kiri

68

.33

68.3

3 68

.33

11.0

111

.01

11.0

1 -2

9.19

-2

9.19

-2

9.19

3.

56

3.56

3.

56

Si

ak

111,

98

492,

36

238,

57

13,1

020

,01

16,4

2 -2

9,12

-2

8,07

-2

8,72

0,

32

4,02

2,

00

S.

Tap

ung

Kan

an

187.

83

187.

83

187.

83

13.6

313

.63

13.6

3 -2

6.16

-2

6.20

-2

6.20

4.

59

4.60

4.

60

M

anda

u 25

4.46

27

6.40

26

5.43

17

.76

20.9

319

.34

-29.

40

-29.

40

-29.

40

3.20

3.

20

3.20

July

/Aug

ust 2

005

S. T

apun

g K

iri

77.4

4 27

4.98

16

2.38

9.

43

14.9

311

.85

-30.

05

-27.

20

-28.

90

3.51

6.

55

4.54

Si

ak

156,

06

441,

69

240,

71

11,6

120

,56

15,5

0 -2

9,36

-2

7,92

-2

8,90

-0

,46

6,55

2,

95

S.

Tap

ung

Kan

an

168.

51

277.

31

211.

45

13.6

719

.75

16.2

6 -3

0.15

-2

8.97

-2

9.57

0.

83

7.42

4.

27

M

anda

u 20

0.58

21

4.72

20

6.13

18

.64

22.0

920

.25

-30.

48

-29.

64

-29.

98

3.25

4.

60

3.81

Mar

ch 2

006

S. T

apun

g K

iri

n.d.

n.

d.

n.d.

n.

d.

n.d.

n.

d.

n.d.

n.

d.

n.d.

n.

d.

n.d.

n.

d.

Si

ak

120,

82

315,

72

210,

30

15,5

918

,56

17,2

6 -2

9,27

-2

8,32

-2

8,83

3,

14

5,18

4,

25

S.

Tap

ung

Kan

an

n.d.

n.

d.

n.d.

n.

d.

n.d.

n.

d.

n.d.

n.

d.

n.d.

n.

d.

n.d.

n.

d.

M

anda

u n.

d.

n.d.

n.

d.

n.d.

n.

d.

n.d.

n.

d.

n.d.

n.

d.

n.d.

n.

d.

n.d.


Likewise wastewater discharges may be also responsible for the higher DIN

concentrations in the S. Tapung Kiri close to the village Kualakandis (river km ~140)

(Fig. 1, 3a). However, due to high oxygen contents (4.4 to 5.5 mg L-1) the contribution

of NH4+ to DIN remained relatively low in the S. Tapung Kiri (Fig. 3b).

Tab. 3: Dissolved inorganic nitrogen (DIN), ammonium (NH4

+) and phosphate (PO43-)

concentrations of wastewater channels draining the city of Pekanbaru.

In addition to wastewater discharges leaching from soils is generally considered to be

a main DIN source in rivers which in former studies also was identified to be the

major source of DOC in the Siak (Baum et al., 2007). DOC/DIN ratios determined in

freshwater samples of the Siak mainstream vary between 17 and 85 and fall in the

range of C/N ratios measured in peat and leaf samples collected along the river

banks indicating that leaf litter as well as peatsoils are also sources of DIN in the Siak

(Fig. 6). Since peatsoils in the Siak catchment are already heavily disturbed by the

conversion of peat swamp forests into oil palm plantations, leaching cannot be

considered to be a purely natural process. However, so far the anthropogenic impact

is difficult to quantify.

Wastewater channels DIN [μmol L-1] NH4+ [μmol L-1] PO4

3- [μmol L-1]

Il. Karag 1,377.0 1,242.3 106.2

S. Sail Cont. 772.6 645.8 63.7

S. Sail 633.9 499.5 58.4

Il. Riau 1,481.8 1,292.3 86.8

Il. Riau 2 1,482.6 1,235.8 77.7

S. Hitam 564.4 347.9 51.6

Il. Juanda 1,877.1 1,510.5 99.9

Riau 373.5 263.3 192.1

Karag 722.4 664.3 179.4


Fig. 6: DOC versus DIN concentrations of freshwater samples taken in the Siak mainstream during the sampling campaigns in March (dots) and September (grey circles) 2004, July/August 2005 (white circles) and March 2006 (filled squares). Maximum and minimum C/N ratios of peat and leaf samples are marked as black and dashed lines.

As mentioned above the DIN concentrations measured during the expedition in

March 2004 were twice as high as those determined during the other expeditions

(Fig. 3a). However, DOC as well as phosphate concentrations, which will be

discussed below, hardly reflect an enhanced leaching from soils in March 2004. Due

to unchanged DOC but enhanced DIN concentrations the DOC/DIN ratios observed

during March 2004 were much lower than during the other periods of investigation

(Fig. 6). Oil palm plantations, which cover large areas of the Siak drainage basin, are

usually fertilized with artificial nitrogen fertilizer at the end of the rainy season every

year (personal communication). The high precipitation rates in March 2004 which

followed an already dry February could have therefore enhanced leaching of recently

fertilized nitrogen resulting in increased DIN concentrations in the Siak in March.

Despite wastewater discharges and possible anthropogenic enhanced leaching DIN

concentrations in the Siak river upstream the estuary ranged between ~8 and 65


μmol L-1 (Tab. 1, Fig. 3a) which is much lower than the concentrations measured in

non-blackwater rivers in Indonesia (>100 μmol L-1) (Jennerjahn et al., 2004). DIN

concentrations measured in the peat-draining South Sumatran river Musi in 1973/74

prior to the main deforestation were reported to range between 0.7 and 14.3 μmol L-1

(Kobayashi et al., 1979) which indicates that changes in land-use and wastewater

discharges could have led to a substantial rise in DIN levels in the Siak.

Phosphate (PO43-)

Overall phosphate (PO43-) concentrations ranged between 0.2 and 17.7 μmol L-1 and

exhibited a similar distribution pattern as DIN concentrations during all campaigns

(Tab. 1, Fig. 3c) with enhanced concentrations between Pekanbaru and Perawang

(river km ~180-230). Since the Pekanbaru wastewater channels reveal a mean PO43-

concentration of 102 μmol L-1 (Tab. 3) it could also be assumed that wastewater

discharges increased the PO43- concentrations in this area. Even higher PO4

3-

concentrations of up to 197 μmol L-1 were measured near industrial sites located

upstream Pekanbaru (Fig. 3c). Since these locally restricted PO43- peaks were hardly

reflected in the DIN concentrations they were probably caused by industrial rather

than by urban wastewater discharges. Probably this industrial sewage contains lower

amounts of DIN than urban wastewaters. PO43- peaks were most pronounced in

September 2004 and may be attributed to reduced dilution of wastewater in the rivers

probably due to low river discharges and precipitation rates (Baum et al., 2007)(Fig.

2).

Conclusions As expected for a classical blackwater river, nutrient concentrations are much lower

in the Siak than in non-blackwater rivers in Indonesia and world-wide. Although

nutrient uptake by water hyacinths might act locally as a nutrient sink, nutrient uptake

by freshwater plankton seems to play only a minor role in the Siak. Industrial and

urban wastewater discharges as well as anthropogenic affected soil leaching and

washout of nitrogen fertilizer are the main nutrient sources in the Siak. Despite

nutrient concentrations that are low compared to non-blackwater rivers, human

impact could have doubled the DIN concentration in the Siak as indicated by

comparison of the Siak data with those measured prior to the main deforestation in

the South Sumatran peat-draining Musi River.


Acknowledgements We would like to thank all students and scientists from the University of Riau

(Pekanbaru, Sumatra) for their help during our field and laboratory work. Particularly

we would thank Csilla Kovacs for her valuable support during the expeditions and in

the lab. We are also grateful to Venugopalan Ittekkot and Esther Borell for their

useful comments on the manuscript and proofreading. We also acknowledge

financial support through the Federal German Ministry for Education, Science,

Research and Technology (BMBF, Bonn) (Grant No. 03F0392C-ZMT, Grant No.

03F0392B-Terramare).


2.2. The Siak, a tropical black water river in central Sumatra on the verge of

anoxia

Tim Rixena, Antje Bauma, Thomas Pohlmannb, Wolfgang Balzerc, Joko Samiajid,

Christine Josed

a Zentrum für Marine Tropenökologie, Fahrenheitstr. 6, 28359 Bremen, Germany b Zentrum für Meeres- und Klimaforschung, Institut für Meereskunde, Universität Hamburg, Bundesstr.

53, 20146 Hamburg, Germany cUniversität Bremen, FB2 Meereschemie (UBMCh), Postfach 330440, 28334 Bremen, Germany dUniversity of Riau, Jl. Simpang Panam Km 12.5, Pekanbaru, Riau, Indonesia

Biogeochemistry, submitted 10 June 2008

Abstract The Siak is a black water river in central Sumatra, Indonesia, which owes its brown

color to dissolved organic matter (DOM) leached from surrounding, heavily disturbed

peat soils. The dissolved organic carbon (DOC) concentrations measured during five

expeditions in the Siak between 2004 and 2006 are among the highest reported

world wide. The DOM decomposition appeared to be a main factor influencing the

oxygen concentration in the Siak which showed values down to 12 μmol l-1. Results

derived from a developed box-diffusion model indicated that in addition to the DOC

concentration and the associated DOM decomposition the water-depth also plays a

crucial role in regulating the oxygen levels in the river. The water-depth could affect

the oxygen input across the air-water interface and the oxygen consumption in the

total water column because of its impact on the turbulence in the aquatic boundary

layer and the volume of water in the river. Model results imply furthermore that a

reduced water-depth could counteract an increased oxygen consumption caused by

an enhanced DOM leaching during the transition from dry to wet periods. This buffer

mechanism seems to be close to its limits as indicated by sensitivity studies which

showed in line with measured data that an increase of the DOC concentrations by

~15% could already lead to anoxic conditions in the Siak. This emphasizes the


sensitivity of the Siak against further peat soil degradation, which is assumed to

increase DOC concentrations in the rivers.

Keywords: anoxia, black water river, peat, Sumatra

Introduction In recent years there has been an increasing number of reports on anoxic (zero

oxygen) and hypoxic (oxygen concentration < 5 μmol l-1) events occurring in

estuaries and coastal zones (Turner and Rabalais, 1994; Rabalais, 1999; Naqvi et

al., 2000; Diaz, 2001). These events were often caused by eutrophication but there

are also natural processes such as black water events that lead to anoxic and

hypoxic conditions in rivers and estuaries (Hamilton et al., 1997; Howitt et al., 2007).

Black water events are flood events during which an enhanced leaching of DOM from

leaf litter colors the water dark brown; the subsequent decay thereof reduces the

oxygen concentration in the water. Although oxygen consumption is generally

considered to be the main cause of low oxygen levels in aquatic systems, the oxygen

concentrations in the water are the product of a complex interplay between oxygen

consumption and ventilation (Paerl, 2006). This interplay has not yet been studied in

black water rivers draining the Indonesian peat lands.

Indonesia holds approximately 56% of the tropical peat soils (~20.0 1010 m2)(Rieley

et al., 1996a) that sequestered as much organic carbon (10 – 30 Tg C yr-1) as the

global deep sea sediments in their original state (Sorensen, 1993; Jahnke, 1996).

Today approximately 45% of the former Indonesian peat swamp forest has been lost

and large parts of the peat lands have been converted into rubber estates and

particularly oil palm estates (Angelsen, 1995; Harrison et al., 2005). Due to aerobic

peat decomposition and fires kindled by common agricultural slash-and-burn

practices, disturbed peat lands turned into CO2 sources. Current estimates on CO2

emissions from drained Indonesian peat lands are at >485 Tg C yr-1 and thus even >

4 times higher than the Indonesian CO2 emissions caused by burning fossil fuel,

cement production and gas flaring (103 Tg C yr-1 in 2004)(Marland et al., 2007). The

dramatic destabilization of Indonesian peat lands and the resulting mobilization of

carbon emphasize the need to assess the vulnerability of tropical peat-draining rivers


such as the Siak in central Sumatra against associated environmental changes (Fig.

1). Therefore five expeditions to the Siak were carried out between 2004 and 2006

during which DOC, oxygen, salinity and temperature were measured along the river.

Furthermore, DOM decomposition experiments were conducted and a box-diffusion

developed in order to study the oxygen dynamic in the river.

Fig. 1: Study area: The Siak with its headstreams S. Tapung Kiri and S. Tapung Kanan, and its tributary Mandau. The locations of the main cities (Pekanbaru, Perawang, and Siaksriindrapura) are indicated by triangles. Peat soil distribution (marked in green) is obtained from the FAO (2003). Samples collected during the expedition in March and September 2004 as well as in July/August 2005 and March 2006 are indicated by the light grey, dark grey, white, and black circles, respectively. In order to keep the figure as clear as possible the sampling sites during the November 2006 expedition which are also located between Pekanbaru and the Bengkalis Strait, were not shown.

Study area and Methods Central Sumatra experienced high rainfall and a weakly pronounced seasonality with

a dry season (May – September) and a rainy season (October – April) due to the

meridional variation of the inter-tropical convergence zone (Fig. 2). On inter-annual

time scales the precipitation rates are assumed to have been influenced by the


climate anomaly El Niño/Southern Oscillation (ENSO, Ropelewski and Halpert,

1987). During our expeditions between 2004 and 2006 ENSO forcing was moderate

compared to the pronounced El Niño event in 1997/98 in the course of which the

Southern Oscillation Index (SOI) revealed values < -5. Nevertheless, weakly

pronounced El Niño conditions prevailed during the dry season 2005 and 2006

whereas ENSO was in positive mode referred to as La Niña during the rainy season

2005/2006.

Fig. 2: Precipitation rates obtained from DWD (2006) and averaged for the area 1°S – 1°N and 100-102°E are indicated by the grey bars. The dark grey bars show the months during which the expeditions were carried out. The black bold line shows the precipitation rates smoothed with a three-month moving average. The Southern Oscillation Index (SOI) was obtained from http://www.cpc.ncep.noaa.gov/data/indices/soi) and also smoothed with a three-month moving average.

The Siak is one of the main peat-draining rivers in central Sumatra in which high

DOM inputs caused by leaching from the surrounding peat soils has reduced light

penetration to depths of ~15 - 20 cm (Baum et al., 2007). The Siak originates at the

confluence of the headstreams S. Tapung Kanan and S. Tapung Kiri (Fig. 1). It

passes through the adjacent lowlands and discharges into the Malacca Strait after


370 km. The S. Tapung Kanan and the Mandau, the main tributaries of the Siak,

originate in the peat swamps and join the Siak at river km 155 and 245, respectively.

The Siak catchment (11.500 km2) consists to approximately 45% of peat lands which

have largely been converted into palm oil and rubber estates as well as shrub lands

(Laumonier, 1997).

Tab.1: Sampling period, mean water temperatures, precipitation rates obtained from (DWD, 2006, see Fig. 2), water discharges as derived from the precipitation rates (see Baum et al. (2007), for more detailed information), DOC riverine end-member concentrations as indicated by the regression equations shown in Fig. 4a.

Sampling period Temp. Precipit. Discharge DOC

Month Year [°C] [mm] [m³s-1] [μmol l-1]

March 2004 29.4 327 645 1866*

September 2004 30.1 199 391/99** 2195

July/August 2005 29.5 304 599 2247

March 2006 30.5 254 500 1613

November 2006 29.7 180 355 1793

mean 29.8 253 498/440 1942

* This riverine DOC end-member concentration was estimated based on DOC concentrations measured in the Siak upstream the estuary as no samples were taken in the estuary during the expedition in March 2004 (see Baum et al., 2007). ** The measured water discharge was 99 m3 s-1 (see Baum et al. 2007).

During the five expeditions to the Siak between 2004 and 2006 (Tab. 1) water

samples for determining DOC, dissolved oxygen and salinity were taken using a

Niskin bottle at a water-depth of one meter along the river (Fig. 1, 3). All samples

were taken during day time. The DOC samples were filtered through 0.45 μm filters

into pre-combusted 20 ml FIOLAX ampoules. The samples were subsequently

acidified (20% phosphoric acid) to a pH value of ~2, sealed, and stored at ~4°C in

darkness until they were analyzed after the expeditions. DOC was analyzed using a

high temperature catalytic oxidation method (Dohrman DC-190 analyzer). Oxygen

concentrations were determined using Winkler titration and salinity was measured by

a WTW Tetra Con 325_3. A more detailed description of the methods applied is

given by Baum et al. (2007). During the third expedition, oxygen, salinity and

temperature profiles were also obtained using a Sea-Bird SBE19plus. Due to


logistical constraints the sampling campaign was restricted to the upper course of the

Siak in March 2004 and oxygen concentrations could not be measured during the

last expedition in November 2006.

In March 2006, a DOM microbial and photochemical degradation experiment was

initiated for which water was collected a few km downstream the Mandau junction

(Fig. 1). The water collected was immediately filled into eight ~ 20 ml FIOLAX

ampoules. The half-filled ampoules were sealed and exposed to sunlight until they

were opened and preserved as the other DOC samples. The DOC concentrations

measured in each of the incubated ampoules were plotted against the time at which

the ampoules were opened (Fig 4). Since we left the study site after 336 hrs (14

days), the remaining incubated sample was exposed to artificial sunlight (Ocean light

150 HQ I) until it was analyzed after 3148 hrs (131 days). The UV-transmittance of

the FIOLAX glass ampoules was determined using a spectrophotometer (Libra S12)

with sensors for UV-A (315 to 400 nm) and UV-B (280 to 315 nm). The results

showed that ~5% of the UV-A and ~38% of the UV-B irradiance were absorbed by

the glass ampoules. Since the UV absorption and the artificial sunlight could have

reduced the photochemical degradation, the DOM decay determined in the

experiment must be considered to be an underestimate rather than an overestimate.

Results and Discussion DOC concentration

The DOC concentrations in the Siak increased from approximately 500 to 1300 and

from 1300 to 1900 μmol l-1 around the Kanan/Kiri and Mandau junctions due to high

DOM inputs from peat-draining lowland rivers S. Tapung Kanan and Mandau (Fig. 1,

3a) (Baum et al., 2007). The Mandau, which is assumed to contribute half of the

DOM that was carried into the Siak estuary, revealed DOC concentrations of as

much as 3600 μmol l-1. According to global compilations (Hope et al., 1994; Harrison

et al., 2005), such a high DOC concentration has only been topped by one river (the

Oyster river). Rising DOC concentrations in rivers were suggested to indicate a

destabilization of peat soils at higher latitudes caused by climate change (Freeman et

al., 2001; Freeman et al., 2004). In the Siak catchment peat soils are destabilized by

deforestation, drainage, and conversion of peat swamp forests into palm oil and

rubber estates as mentioned earlier. Accordingly, peat soil leaching and the resulting


high DOC concentrations in the Siak and its tributaries can not be considered natural.

On the other hand an anthropogenic enhanced leaching as seen in other studies

(Holden et al., 2004; Holden, 2005) is very difficult to quantify as there is no data

available on the Siak prior to the main deforestations.

Fig. 3: DOC (a) and oxygen concentrations (b) measured at a water-depth of 1 m versus river-km. The river-km zero represents the origin of the S. Tapung Kiri in the highlands. At river-km 320 increasing salinity indicates the beginning of the estuary (salinity data are not shown) and at river-km 370 the Siak discharges into the Malacca Strait. The Kanan/Kiri and the Mandau junctions are at river-km 155 and 245. The mean oxygen and DOC concentrations in the Mandau and S. Tapung Kanan are shown by the large black squares. Data measured during the first, second, third, fourth and fifth expeditions are indicated by stars, diamonds, squares, circles and open circles. The averaged DOC and oxygen concentrations are shown by the grey lines and the broken line in ‘b’ indicates the mean oxygen saturation concentrations calculated after Benson and Krause Jr. (1984).


In the estuary, decreasing DOC concentrations correlating to increasing salinity

suggested that dilution of the DOM-rich Siak water by DOM-poor ocean water was an

important factor controlling the DOC concentration in the estuary (Fig. 5).

Fig. 5: DOC concentrations (circles – Sep. 2004, July/August 2005; squares - March 2006, triangles – November 2006) versus salinity. DOC concentrations at the zero intercept of the y-axis are considered as the riverine DOC end-member concentrations (see Tab. 1).

The zero intercept of the y-axis as shown by the regression equation is often

considered as riverine DOC end-member concentration (e.g., Mantoura and

Woodward, 1983; Alvarez-Salgado and Miller, 1998; Miller, 1999). Since no data was

available on the estuary in March 2004, the riverine DOC end-member

concentrations were estimated to be 1866 μmol l-1 based on the DOC concentrations

measured close to the Mandau junction (Baum et al., 2007). However, the DOC end-

member concentrations determined during the expeditions varied between 1613 and

2247 μmol l-1 whereas reduced DOC end-member concentrations were obtained at

the end of the rainy season in March 2004 and 2006 and during the dry season 2006

(Fig. 2, Tab.1). Enhanced DOC end-member concentrations were measured at the


end of the dry season in September 2004 and in July/August 2005 suggesting, as

also observed in other studies (Hamilton et al., 1997), that increasing precipitation

rates enhance DOM leaching from soils, especially after dry periods. During the

expedition in September 2004, a low ground water level still attested to the preceding

dry period and the water discharge measured was significantly lower than the one

derived from the precipitation rates (see Tab. 1). It was therefore assumed that the

increasing precipitation rates were still filling up the ground water reservoir (Baum et

al., 2007).

DOM decomposition

The DOM decomposition experiment showed that downstream the Mandau junction

approximately 27% of the DOC (~374 μmol l-1) was degradable within a two week

period whereas 73% of the DOC appeared to be refractory on the considered time

scales of days to months (Fig. 4).

Fig. 4: DOM decomposition experiment which shows decreasing DOC concentrations (circles) with increasing time of incubation. Note that the scale of the y-axis changes at 1000 μmol l-1. The grey shaded area represents the part of the DOC which appears to be refractory against microbial and photochemical oxidation on the considered time scale. The given function describes the exponential decomposition of the degradable DOC as shown by the black line. By fitting the exponential function to the data, the two outliers as indicated by the open circles, were ignored.


Since peat reveals a ratio between organic carbon and oxygen (C/O ratio) of ~2.7

(Cameron et al., 1989), it was assumed that only 0.8 mol of dissolved oxygen was

consumed during oxidation of one mol of peat-derived DOM (DOM + 0.8 O2 -> CO2).

Consequently the DOM decomposition rate (eq. 2) can be converted into the oxygen

consumption rate (COxygen) by multiplying it by 0.8:

ttDOCCOxygen �

��

)(*8.0 (3)

According to eq. 1 – 3, a mean DOC concentration of ~ 1500 μmol l-1 (DOCt0) as

derived from the data measured in the Siak upstream the estuary (Fig. 3 a),

suggests, for example, a mean oxygen consumption rate of ~ 5.1 μmol l-1 hr-1. Such

an oxygen consumption rate is ~3 times higher than those determined in the Amazon

river (1.7 μmol l-1 hr-1 (Devol et al., 1987) and must even be considered as an

underestimate as indicated above. However, such a high DOC decomposition rate

implies that the DOC concentrations should have decreased with the water travel

time in the Siak river. Instead, the DOC concentrations increased from headwater to

estuary, suggesting that DOC inputs exceeded the DOC decay; this imbalance was

most pronounced at the Kanan/Kiri and the Mandau junctions mentioned above (Fig.

3a).

Oxygen concentrations

Oxygen concentrations decreased from ~170 μmol l-1 in the S. Tapung Kiri to 12

μmol l-1 at the beginning of the Siak estuary (Fig. 3b) and revealed hardly any vertical

gradients as seen in the oxygen profiles obtained by the Sea-Bird19plus CTD during

the expedition in July/August 2005 (Fig. 6).


Fig. 6: DOC and oxygen concentrations measured in the Siak downstream river-km 180 at a water depth of one m (upper panel) versus latitude as well as oxygen concentrations, salinity and temperature determined with the Seabird CTD versus latitude (lower panels). In the lower panels the grey area indicates the river bed and the black lines the CTD casts.

The oxygen concentrations were inversely correlated to the DOC concentrations

suggesting that DOM decomposition was a main factor controlling the oxygen

concentration in the Siak (Fig. 7). Furthermore, the regression equation and the

resulting zero intercept of the x-axis, implies that anoxic conditions should be


established in the Siak when the DOC reaches concentrations of ~2852 μmol l-1.

(=145.48/0.051; see equation given in figure 7). In the Paraguay river, for example,

an enhanced DOM leaching after a dry period and the resulting increase of the DOC

concentrations from ~ 700 to 925 μmol l-1 was already sufficient to produce an anoxic

event and an associated fish kill (Hamilton et al., 1997). There are also reports of

mass fish mortalities in the Siak but so far we were not able to observe such an

event.

Fig. 7: Oxygen versus DOC concentrations measured at water-depth of 1 m during the expeditions. The black line illustrates the given regression equations, ‘n’ is the number of data points and ‘r’ is Pearson correlation coefficient. The arrow indicates the data which show that an increasing DOC concentration is not necessarily associated with reduced oxygen concentrations.

However, although the correlation between DOC and oxygen concentrations is

statistically significant (significance level < 0.1%) in the Siak, there are also data

showing that an increase of the DOC concentration from ~1000 to 2550 μmol l-1 was

not always be associated with the drastic decline in the oxygen concentration. These

data might be considered as outliers but they could also point to processes which

could counteract the impact of an enhanced DOM decomposition rate on the oxygen

concentration in the Siak.


Oxygen inputs

Oxygen production during the photosynthesis of organic matter could in principle be

an oxygen source which might have enhanced the oxygen concentrations in the Siak

during the daytime. Since the lack of light caused by the brown water color strongly

reduces photosynthesis, it is assumed that oxygen inputs across the air-water

interface are the main source of oxygen in the Siak. This oxygen flux (FOxygen) is

driven by the oxygen partial pressure (pO2) difference between the river and the

atmosphere and can be calculated according to Fick’s law:

FOxygen=k * � (pO2-Atmospere – pO2-River) (4)

‘�’ is the temperature and salinity dependent solubility coefficient of oxygen (�=[O2]/

pO2) which was calculated according to Benson & Krause Jr. (1984). ‘k’ is the piston

velocity, which is mainly controlled by the turbulence in the aquatic boundary layer.

The turbulence in the aquatic boundary layer strongly depends on the bottom friction

and can be increased by wind speeds and precipitation rates (e.g., Raymond and

Cole, 2001; Kremer et al., 2003; Borges et al., 2004; Guerin et al., 2007). The bottom

friction, in turn, generally increase with decreasing water-depth and increasing

current velocity (Raymond and Cole, 2001). However, results derived from the

Amazon, by determining 222Rn accumulation in free-floating chambers and carrying

out oxygen mass balances, indicate mean piston velocities of up to 7 and 25 cm hr-1,

respectively (Devol et al., 1987).

Oxygen dynamic

In order to examine the interplay between oxygen consumption and oxygen input, we

developed a small box-diffusion model (eq. 5) within which the water column of the

river was divided into 100 cm thick layers (�z) and a time step of 13.5 s was

considered.

CS+zOA

ztO

OxygenOxygenV ��

�

��

��

�� 22

(5)

SOxygen is the oxygen source term in the surface layer. If in a discrete model the

surface layer has a thickness �z, the oxygen source term in this layer can be derived


from the oxygen flux through the sea surface (F Oxygen, see eq. 4) by means of: S

Oxygen = F Oxygen / �z. COxygen (see eq. 3) is the oxygen consumption rate in the water

column and ‘AV’ is the diffusion coefficient for which a value of 370 cm2 s-1 was

selected. Determination of the diffusion velocity udiff by means of tAu Vdiff /2 �� ,

leads to the conclusion that due to the mean water depth of < 20 m (see Fig. 6)

diffusion affects the entire water column after approximately ~1.5 hrs. Accordingly it

is inferred that a variation of the chosen AV in a realistic range would also result in a

rapid mixing which agrees with the well-mixed water body seen in the salinity and

temperature profiles (Fig. 6). Eq. 5 is formulated forward in time and as central

differences in space. An explicit scheme was employed to solve this equation, which

made it necessary to use the above-mentioned small time step of 13.5 s. A test of

this scheme prior to our simulation proved that it fulfils all mass conservation

requirements.

Water-depth and piston velocity

In order to check the applicability of the model for the Siak, we firstly averaged the

DOC and oxygen concentrations measured upstream the estuary. The resulting

mean DOC concentration of 1500 μmol l-1 was used to calculate the oxygen

consumption (eq. 3) and after reaching the steady state, the simulated oxygen

concentration was compared to the mean measured oxygen concentrations of 59

μmol l-1. The modelled oxygen concentrations varied depending on the selected

piston velocity and the water-depth. As discussed previously the piston velocity

strongly influences the oxygen input across the air-water interface and the water-

depth affects the total oxygen consumption in the water column. The total oxygen

consumption within a given time is the product of the oxygen consumption rate (see

eq. 3) and the considered water volume. Since the time step of 13.5 s and the

considered surface area are constant in the model, the total oxygen consumption

increases with an increasing water-depth. One therefore has to increase the piston

velocities if one enhances the water-depth in order to produce an oxygen

concentration of 59 μmol l-1 in the modeled water column (Fig. 8). A piston velocity of

22.9 cm hr-1 would, for example, call for a water-depth of 8 m, in order to simulate a

mean oxygen concentration of 59 μmol l-1 (Fig. 9, see also Tab. 2 – experiment 1).


Tab. 2: Experiment number, topic of the experiment, DOC concentrations used in the model runs, modeled oxygen concentrations at the beginning estuary (see Fig. 10, 12), and the associated oxygen consumption rates as well as the used piston velocity (k), current velocity, water-depth, and temperatures during the model experiments. ‘low ground’ and ‘l.g.’ means low groundwater levels.

Experiment Topic DOC O2 O2-cons. k velocity water-depth Temperature

No. [μmol l-1] [μmol l-1] [μmol l-1hr-1] [cm h-1] [m s-1] [m] [°C]

1 average 1500 59 5.18 22.9 8 29

2 velocity 1900 67 6.56 25.0 1.000 8 29

3 velocity 1900 41 6.56 25.0 0.500 8 29

4 velocity 1900 32 6.56 25.0 0.250 8 29

5 velocity 1900 31 6.56 25.0 0.125 8 29

6 temperature 1900 28 6.56 25.0 0.250 8 30

7 water-depth 1900 58 6.56 25.0 0.250 7 29

8 DOC 2185 1 7.55 25.0 0.250 8 29

9 low ground. 2550 22 8.80 28.1 0.250 7 29

10 l.g. DOC 2932 0 10.10 28.1 0.250 7 29

Fig. 8: Piston velocities (k) versus water-depth. Each data point indicates a model result. In each model run a DOC concentration of 1500 μmol l-1 was considered, and to each given water-depth a piston velocity was selected in a way that the oxygen concentration in a steady state was 59 μmol l-1. This means that assuming a DOC concentrations of 1500 μmol l-1 the model will produce an oxygen concentration of 59 μmol l-1 if one selected a water-depth and a piston velocity which is located on the given line.


Such a mean water-depth appears to be representative for the Siak considering that

the water-depth at our sampling sites ranged between ~ 8 and 20 m (see Fig. 6) and

the sites were located near the centre and not close to the river banks. Since a piston

velocity of 22.9 cm hr-1 is also close to the one derived from the oxygen mass

balance calculation in the Amazon (Devol et al., 1987), it can be concluded that the

our model is suitable to study the oxygen dynamics in the Siak river.

Residence time and current velocities

As indicated by the previous model run (see Fig. 9) it takes up to 120 hrs (5 days) to

reach a steady state so that the residence time of water in the Siak and thus the

current velocity could be an important factor influencing the oxygen concentration in

the river.

Fig. 9: Oxygen concentrations derived from the model versus time (a) and water-depth at steady state (b; see Tab. 2 experiment 1).

In order to study the possible impact of the current velocity on the oxygen

concentration we chose a piston velocity of 25 cm hr-1 and a mean water-depth of 8

m and plotted the modeled oxygen concentrations versus ‘river-km’ (Fig. 10 a). River-

km was calculated by multiplying the time-step of 13.5 s and current velocity. The

product was kept constant by reducing the number of time-steps in the simulation

when the current velocity was increased. Furthermore, the initial DOC concentration

was set at 520 μmol l-1 as measured in the S. Tapung Kiri (see Fig. 3 a) and was


subsequently increased on a step by step basis at river-km 105 and 215 to 1300 and

1900 μmol l-1 in order to simulate DOM inputs from the S. Tapung Kanan and

Mandau. The selected river-km’s are actually ~30 – 50 km prior to real Kanan/Kiri

and Mandau junction at river km 155 and 245. The shift reflects the tidal influence at

the Mandau junction and DOM inputs of smaller peat draining creeks into to the S.

Tapung Kiri already prior to the Kanan/Kiri junctions. However, a selected mean

current velocity of 1 m s-1 results in oxygen concentrations which are higher than

those measured because of the short residence time (~2.4 days) and a resulting

lower DOM consumption in the river (Fig. 10 a, Tab. 2 – experiment 2). If one selects

mean current velocities (residence times) of 0.25 m s-1 (~9.8 days) and 0.125 m s-1

(~18 days), the resulting oxygen concentrations correspond reasonably well with the

measured oxygen concentrations in the Siak (Fig. 10 a, Tab. 2 - experiments 4 and

5). Direct determination of mean current velocities in tidal-influenced rivers is very

problematic but can be deduced from the mean water discharge and the mean river

cross section. A mean water discharge of 440 m3 s-1 (Tab. 1), a mean water-depth of

8 m as indicated by the model results and a river-width of 220 m would, for example,

suggest a mean current velocity of ~0.25 m s-1. Since the Siak already reveals a

width of 80 m at the Kanan/Kiri junction which increases to 250 m at the Mandau

junction and to > 350 m at the beginning of the estuary, a mean river-width of > 220

m and therefore also a mean current velocity of < 0.25 m s-1 would appear to be

acceptable.


Fig. 10: (a) Oxygen concentrations calculated by using a mean current velocity of 1 (black line), 0.5 (dotted line), 0.25 (bold line), and 0.125 m s-1 (bold broken line) versus river-km (see Tab. 2 experiments 2 – 5). (b) Oxygen concentrations calculated by using a current velocity of 0.25 m s-1 (bold line, Tab. 2 – experiment 4). The same current velocity was used also by the other model runs during which the temperature was increased by 1°C (stippled line, Tab. 2 - experiment 6), the water-depth was decreased by 1 m (dotted line, Tab. 2 experiment – 7) and the DOC concentration was increased by 15% (thin black line, Tab.2 – experiment – 8). The bold grey indicated the mean measured oxygen concentrations as shown in figure 3b.


Sensitivity experiments

Temperature, water-depth, DOC

Sensitivity experiments were carried out in order to investigate the impact of possible

environmental changes on the oxygen concentration in the Siak. We therefore

increased the temperature and reduced the water-depth in the model because of

changes in precipitation rates and the river discharge as observed, e.g., during the

expedition in September 2004 (Fig. 10b). Furthermore the DOC concentrations were

also increased due to a possible anthropogenic enhanced DOM leaching.

Temperature changes affect the oxygen input across the air-water interface by their

impact on the solubility of oxygen in the water (see eq. 4, Benson and Krause Jr.,

1984). In the model a temperature increase of 1°C would lower the oxygen

concentrations by ~4 μmol l-1. A reduction of the water-depth would increase the

oxygen concentrations by ~26 μmol l-1 (Fig. 10 b, Tab. 2 – experiments 6 and 7)

because it would lower the total oxygen consumption in the water columns as

discussed above. An increase of the DOC concentration by 15% after the Mandau

junction would already suffice to produce anoxic conditions in the Siak upstream the

estuary (Tab. 2 – experiment 8).

Enhanced DOC concentrations at the end of dry period

Increasing the mean DOC concentration by 15% would result in a DOC concentration

of 2185 μmol l-1 between the Mandau junction and the estuary. This concentration

falls below DOC concentrations of ~ 2550 μmol l-1 measured in this area e.g., during

the expedition in September 2004 (Fig. 3 a). Although these high measured DOC

concentrations were associated with low oxygen concentrations, the latter still varied

around 20 μmol l-1 and were not zero as indicated by the sensitivity experiment (Fig.

3b, 7). As also mentioned previously, the groundwater level was extremely low during

this expedition due to dry conditions prior to the expedition. In addition to a decrease

of the total oxygen consumption, a low ground water level and the resulting reduced

water-depth could also enhance the turbulence in the aquatic boundary layer and

thus the piston velocity and the oxygen flux across the air-water interface. We carried

out further sensitivity experiments in order to test to what extent a reduced water-

depth could counteract an enhanced oxygen consumption rate caused by an

increase in the DOC concentration. Within these experiments the DOC concentration


was set to 2550 μmol l-1 after the Mandau junction and the water-depth was reduced

by up to 5 m (Fig. 11).

Fig 11: Modeled oxygen concentrations at the beginning of the estuary (a) and the used piston velocity (b) versus water-depth used in the model runs. The open circles show oxygen concentrations which result from the constant piston velocity of 25 cm hr-1 as shown in figure b. The black circles indicate the oxygen concentrations which results from model runs in which the water-depth and the piston velocity was changed.


The model results indicated that a drop in the water-depth of 2 m would suffice to

explain an oxygen concentration of > 20 μmol l-1 even if the DOC concentration

reached 2550 μmol l-1. If one also assumes that the piston velocity increases by 12%

when the water-depth decreases by one meter (~12%), a reduction of the water-

depth by one meter could already explain the data measured during the expedition in

September 2004 (Fig. 11, 12, Tab. 2 - experiment 9).

Fig. 12: Oxygen concentrations versus river-km. Oxygen concentrations calculated by using a water-depth of 7 m and a piston velocity of 28.1 cm hr-1 are indicated by the broken black line (Tab.2 – experiment – 9). The impact of an increase of the DOC concentrations by 15% is indicated by the black line (Tab.2 – experiment – 10). The bold grey line indicated the mean measured oxygen concentrations as shown in figure 3b.

To test the sensitivity of this system to an enhanced DOC leaching the DOC

concentrations were again increased by 15% to 2932 μmol l-1. According to the

model results such a DOC increase would again be sufficient to produce anoxic

conditions upstream the estuary (Fig. 12, Tab. 2 - experiment 10). The DOC

concentrations of 2932 μmol l-1 applied correspond fairly well with the zero intercept

of the x-axis (~2852 μmol l-1) derived from the regression equation obtained by the

correlation between the measured DOC and oxygen concentrations (Fig. 7). It is

therefore assumed that changes in water-depth is an important factor which could


counteracts an enhanced DOC leaching and the resulting increased oxygen

consumption rates but its buffer capacity seems to be close to its limits in the Siak.

Conclusion Our results showed that the DOC concentrations increase along the Siak river

because DOM inputs exceed DOM decay. DOM decomposition and the resulting

oxygen consumption fueled by continuous DOM inputs appeared to be a main factor

influencing the oxygen concentration in the Siak. This result could be confirmed by a

box-diffusion model which showed that in addition to the DOC concentration the

water-depth is also an important factor influencing the oxygen concentrations. The

water-depth affects the oxygen input across the air water interface and the total

oxygen consumption in the water columns due to its impact on the turbulence in the

aquatic boundary layer and the water volume in the river. A reduced water-depth

could, for example, compensate for an enhanced oxygen consumption caused by an

increased DOM leaching from soils during the transition from dry to wet periods.

Model results in line with measured data suggest that this buffer mechanism is close

to its limit which emphasizes the sensitivity of the Siak against further peat soil

degradation.

Acknowledgments We would like to thank all scientists and students from the University of Pekanbaru

who helped us during our field work, the rector of the University of Riau, the captain

of the research vessel R/V Senangin and his crew for their support. For helpful

discussion we would like to thank V. Ittekkot, P. Damm our colleagues from the ZMT

and Rena Kerr. We are also grateful to the Federal German Ministry for Education,

Science, Research and Technology (BMBF, Bonn grant number 03F0392C - ZMT)

for financial support and to R. Schlitzer as well as to P. Wessels and W.H.F. Smith

for providing Ocean Data View (ODV) and the generic mapping tools (GMT).


Abbreviations AV diffusion coefficient C carbon COxygen oxygen consumption rate C/O ratio ratio between organic carbon and oxygen cm centimeter DOC dissolved organic carbon DOM dissolved organic matter ENSO El Niño Southern Oscillation FOxygen oxygen flux rate across the air-water interface hr hour k piston velocity km2 square kilometer

l liter

m2 square meter O2 oxygen concentration O2sat oxygen saturation concentration [O2]River oxygen concentration in the river water pO2 oxygen partial pressure pO2-Atmospere partial pressure of oxygen in the atmosphere pO2-River partial pressure of oxygen in the river water t time Tg terra gram S Oxygen oxygen flux through the sea surface into the surface layer SOI Southern Oscillation Index S. Sungai (river) s second udiff diffusion velocity UV ultra violet yr year � solubility coefficient of oxygen �z thickness of the layers in the model μmol micro mol % percent °C degree Celsius


2.3. Relevance of peat draining rivers in central Sumatra for riverine input of

dissolved organic carbon into the ocean

Antje Bauma, Tim Rixena and Joko Samiajib

aCenter for Tropical Marine Ecology, Fahrenheitstr. 6, 28359 Bremen, Germany bUniversity of Riau, Jl. Simpang Panam Km 12.5, Pekanbaru, Riau, Indonesia

Estuarine, Coastal and Shelf Science 73 (2007) 563 – 570; Received 8 August 2006;

accepted 21 February 2007; Available online 16 April 2007

Abstract Sources and discharges of dissolved organic carbon (DOC) from the central

Sumatran river Siak were studied. DOC concentrations in the Siak ranged between

560 and 2,594 μmol l-1 and peak out after its confluence with the river Mandau. The

Mandau drains part of the central Sumatra peatlands and can be characterized as a

typical blackwater river due to its high DOC concentration, its dark brown-coloured,

acidic water (pH 4.4-4.7) and its low concentration of total suspended matter (12-41

mg l-1). The Mandau supplies about half of the DOC that enters the Siak estuary

where it mixes conservatively with ocean water. The DOC input from the Siak into the

ocean was estimated to be ~0.3 Tg C yr-1. Extrapolated to entire Indonesia the data

suggest a total Indonesian DOC export of ~21 Tg yr-1 representing ~10% of the

global riverine DOC input into the ocean.

Keywords: dissolved organic carbon (DOC); peat; Indonesia; Sumatra

Introduction The riverine transport of DOC plays an important role in the carbon cycle as it links

the terrestrial and the marine carbon cycles (Degens et al., 1991; Meybeck, 1993).

Decomposition experiments and studies in polar regions suggest that the majority of

the riverine DOC (63-73%) is decomposed in the ocean within years to decades,

explaining the relatively low contribution (~10%) of terrestrial dissolved organic

matter (DOM) to the marine DOM pool (Meyers-Schulte and Hedges, 1986; Hedges


et al., 1997; Hansell et al., 2004). Such an efficient decomposition implies that

riverine DOC exports act as a source of CO2 to the atmosphere, because

remineralisation of riverine DOC would increase CO2 concentrations and hence the

air-sea gas exchange. Improved understanding and quantification of processes

controlling carbon losses from the terrestrial biosphere are of particular importance

as terrestrial biosphere-soil systems presently act as a sink of anthropogenic CO2

(Keeling et al., 1996).

Present estimates suggest a riverine DOC discharge into the ocean of 170-250 Tg C

yr-1 based on model calculations as well as inventory and extrapolation of data from

selected large global rivers (Ludwig et al., 1996; Hedges et al., 1997; Cauwet, 2002;

Harrison et al., 2005). According to model studies Indonesia contributes ~11% (4.26 *

1012 m3yr-1) to the global freshwater discharge into the ocean (Syvitski et al., 2005).

Despite the high freshwater discharge Indonesia has no major rivers, because it

consists mainly out of relatively small volcanic and coral islands. High precipitation

rates and large areas covered by peat soils (particularly on Sumatra and Borneo),

which are known to be an important riverine DOC source (Freeman et al., 2004),

suggest that Indonesian rivers are important with respect to their input of DOC into

the ocean. However, DOC discharges from Indonesian rivers have not been

investigated in field studies so far. Within the framework of the bilateral joint

Indonesian German project SPICE (Science for the Protection of Indonesian Coastal

Marine Ecosystems), DOC dynamics within the Siak and its tributaries in central

Sumatra were studied in order to quantify the DOC discharge into the ocean.

Study area The Siak is one of the main rivers draining the province of Riau in central Sumatra. It

originates at the confluence of the two headstreams Sungai Tapung Kanan and

Sungai Tapung Kiri, passes through adjacent lowlands and discharges after 370 km

into the Bengkalis Strait which is part of the Malacca Strait (Fig. 1a). The S. Tapung

Kiri has its source at the foot of the western Sumatra highlands whereas the S.

Tapung Kanan and the major tributary Mandau originate in the Central Sumatra

lowlands (Fig. 1a, b).


Fig. 1: Map showing the central Sumatran river Siak with sampling stations in March and September 2004 (black circles = March 2004, white circles = September 2004, black-white circles = March and September 2004), areas covered by peat soils (dark-green coloured) (a) and the elevation model of the Siak catchment area (b).

The climate on Sumatra is dominated by the meridional migration of the Intertropical

Convergence Zone (ITCZ) leading to elevated precipitation rates in March and April

and between October and January. The lowest precipitation rates were observed

between June and August (Fig. 2). However, due to the vicinity to the equator

seasonal variations are only weakly pronounced and precipitation rates during dry

seasons of some years can exceed those during rainy seasons of other years. On


interannual time scale precipitation rates are influenced by the climate anomaly El

Niño Southern Oscillation (ENSO). Negative and positive excursions of ENSO

referred to as El Niño and La Niña decrease and increase precipitation over

Indonesia, respectively (Ropelewski and Halpert, 1987).

Gibbsitic and kaolinitic ferralitic soils (54%) and tropical peat soils (45%) are the

major soil types in the Siak catchment. Its vegetation cover is dominated by oilpalm-

and rubber-estates, lowland forests and shrubs (Laumonier, 1997).

Fig. 2: Mean precipitation rates for 2004 derived from the meteorological station Pekanbaru (black bars) and the GPCC (grey bars) for the Riau Province (0° to 2° N).

Methods Sampling and sample preparation

In 2004 which can be characterised as a weak El Niño year two expeditions were

carried out, one during the wet and one during the dry season in March and

September, respectively (Fig. 1a). Salinity and pH were measured directly with a

WTW TetraCon 325_3 sensor and a WTW pH-electrode SenTix 41. Water samples

were collected with a Niskin bottle. DOC samples were filtered through 0.45 μm filters

into pre-combusted 20 ml glass ampoules. The samples were acidified with


phosphoric acid (20%) to a pH-value of 2 and analysed immediately after the

expeditions.

For the quantification of total suspended matter (TSM) and the determination of

particulate organic carbon (POC) samples were filtered through pre-weighed, pre-

combusted glass fiber filters (Whatman GF/F) and dried at 40° C. Water samples for

the analysis of amino acids were stored frozen in acid-washed PE bottles until

analysis.

Analysis

Dissolved organic carbon

DOC was determined with a Dohrman DC-190 Total Organic Carbon Analyzer using

high temperature catalytic oxidation. The samples were combusted at 680° C within a

quartz column, packed with platinum covered Al2O3-balls. The evolving CO2 was

purified, dried and detected by a non dispersive infrared detection system. The

relative standard deviation for the method was ±2%.

Particulate organic carbon

After removal of inorganic carbon by acidification with 1 N HCl, filters were dried at 40

°C and subsequently analyzed for total carbon and nitrogen in a Carlo Erba NA 2100

elemental analyzer. Within the analyzer the samples were oxidized at 1100 °C and

the formed oxidation products were transported by a carrier gas (He) trough a

reduction tube where NOx was reduced to N2. After removing water and halogens

from the evolving CO2 and N2 the gases were separated and quantified by a thermal

conductivity detector. The relative standard deviation for the method was ±4.5%.

Amino acids

To hydrolyse combined amino acids the filtered water samples were treated with 6 N

HCl under nitrogen atmosphere (24 hrs) at a temperature of 110°C in precombusted

sealed glass bottles. The resulting mixture was adjusted to pH 8.5 using borate buffer

after cooling down to room temperature. Amino acids were analyzed after precolumn

derivatization (Ortho-Phtal(di)aldehyde (OPA) and N-Isobutyryl-L-cysteine (IBLC)) by

high-performance liquid chromatography (Merck HITACHI LaChrom on RP 18-resin)


and detected fluorimetrically (FL Detector L-7480). A more detailed description of the

procedure is given by Fitznar (1999) and Koch (2002).

Estimation of peat soil coverage and slopes in the river catchment

The proportional coverage of peat soils in the Siak catchment was obtained by

digitizing and analyzing the soil map (1:5.000.000) by Laumonier (1997) using

ArcGIS 9. Basin slopes were calculated by using elevation data obtained from the

Global Land Cover Facilities (USGS, 2004) and the “Spatial Analyst Function” in

ArcGIS 9.

Water discharge

The water discharge from the Siak was derived by applying two different approaches.

The first approach is based on water discharge measurements and the area of the

river catchment. The catchment area of 11,500 km² (Atotal) was calculated by using

the created elevation model and the geographic information system ArcGIS 9

including the extension Arc Hydro. As indicated by observations of the current

direction and a tidal range approaching zero the tidal influence during the expeditions

could be traced to ~215 km upstream which is approximately 30 km west of

Pekanbaru close to the sampling site 18/104 (Fig. 1a). Similarly the tidal influence in

the Mandau was traced to station 4/106 (Fig. 1a) indicating that almost the entire

Mandau catchment is tidal influenced. In consideration of the watershed and stream

network one part of the catchment basin affected (At) and one part unaffected (Ant) by

tides were defined. Station 18/104 is regarded as the boundary between both

catchment areas. By means of the elevation data At and Ant were calculated to be

6,696 km2 and 4,804 km2, respectively (Tab. 1). The water discharge at sampling site

18/104 was derived by multiplying the mean current velocity (V) measured by an

Aanderaa Doppler Current Sensor 3900 with the river profile area (Arp) determined by

a Furuno Echolot Model FE 6300 (Tab. 1). The resulting water discharge was

furthermore divided by Ant in order to obtain the water discharge per unit area (q)

which subsequently was multiplied by Atotal for calculating the total river discharge

(Qm) (Tab. 1).

Qm = ((v * Arp)/Ant)* Atotal (1)


In a second approach the total water discharge (Qc) was calculated from the

catchment area (Atotal) and the runoff which is defined as the difference between

precipitation (P) and evapotranspiration (ET) according to the following equation:

Qc = (P – ET) (2)

Precipitation rates were obtained from the meteorological station at Pekanbaru and

from the 1x1° gridded global precipitation data set provided by the Global

Precipitation Climatology Centre (GPCC, 2005) covering the region between 1°S and

1°N and 100° and 102°E for the year 2004 (Tab. 1).

62

P

ublis

hed

and

subm

itted

pap

ers

Tab.

1:

Tota

l (A

tota

l), t

idal

inf

luen

ced

(At)

and

tidal

una

ffect

ed (

Ant

) ca

tchm

ent

area

s; c

urre

nt s

peed

s (V

), riv

er p

rofil

e ar

eas

(Arp

), w

ater

dis

char

ges

(Q18

/104

), di

scha

rges

per

uni

t ar

ea (

q) a

nd m

easu

red

wat

er d

isch

arge

s (Q

m)

mea

sure

d at

sta

tion

18/1

04 i

n M

arch

and

Sep

tem

ber

2004

. D

OC

co

ncen

trat

ions

, mea

n sl

opes

of

the

catc

hmen

t ba

sins

, pea

t so

il co

vera

ges

in t

he c

atch

men

t ba

sins

, cal

cula

ted

wat

er d

isch

arge

s (Q

c), D

OC

exp

orts

an

d D

OC

yie

lds

of t

he S

iak

trib

utar

ies

mea

sure

d in

Mar

ch a

t sa

mpl

ing

site

s 17

, 16

and

8 an

d in

Sep

tem

ber

at s

tatio

ns 1

01, 1

02, a

nd 1

11 a

s w

ell a

s pr

ecip

itatio

n ra

tes

deriv

ed f

rom

the

met

eoro

logi

cal

stat

ion

Peka

nbar

u (P

peka

nbar

u) a

nd t

he G

PCC

(P g

ridde

d) f

or M

arch

, A

ugus

t an

d Se

ptem

ber

2004

.

2004

Mar

ch

Sept

embe

r

Stat

ion

17

16

18

8

101

102

104

111

Riv

er

S.

Tap

ung

Kan

an

S. T

apun

g K

iri

Siak

M

anda

u S.

Tap

ung

Kan

an

S. T

apun

g K

iri

Siak

M

anda

u

Ato

tal

[km

2 ] 2,

335

2,46

9 11

,500

3,

004

2,33

5 2,

469

11,5

00

3,00

4

At

[km

2 ] -

- 6,

696

- -

- 6,

696

-

Ant

[k

m2 ]

- -

4,80

4 -

- -

4,80

4 -

V [m

s- 1]

- -

0.94

-

- -

0.21

-

Arp

[m

2 ] -

- 28

5.4

- -

- 19

6.5

-

Q18

/104

[m

3 s-1]

- -

268.

3 -

- -

41.3

-

q

[l s-1

km-2

] -

- 55

.8

- -

- 8.

6 -

Qm

[m

3 s-1]

- -

642

- -

- 99

-

DO

C

[μm

ol l-1

] 1,

703

615

- 2,

919

1,81

2 57

6 -

3,05

5

mea

n sl

ope

[°]

1.4

2.1

- 1.

7 1.

4 2.

1 -

1.7

Peat

Are

a [%

] 53

.4

3.9

- 48

.1

53.4

3.

9 -

48.1

Qc p

ekan

baru

[m

3 s-1]

149

157

- 19

1 18

19

-

24

Qc

grid

ded

[m3 s-1

] 12

6 13

3 -

162

21

22

- 27

DO

C ex

port

pek

anba

ru

[* 1

010 g

yr-1

] 9.

6 3.

7 -

21.1

1.

2 0.

4 -

2.7

DO

C ex

port

grid

ded

[* 1

010 g

yr-1

] 8.

1 3.

1 -

17.9

1.

3 0.

5 -

3.1

DO

C yi

eld

peka

nbar

u [*

106 g

C y

r-1km

-2]

41.1

14

.8

- 70

.4

4.9

1.7

- 9.

1

DO

C yi

eld

grid

ded

[* 1

06 g C

yr-1

km-2

] 34

.9

12.6

-

59.7

5.

7 1.

9 -

10.4

Mar

ch

Aug

ust

Sept

embe

r

P pe

kanb

aru

[mm

] 35

1 68

23

1

P gr

idde

d [m

m]

297

78

194

Qc

peka

nbar

u [m

3 s-1]

732

91

307

Qc

grid

ded

[m3 s-1

] 61

9 10

4 25

8


Results and Discussion Water discharge

Field observations show a water discharge (Qm) of 99 m3s-1 in September, which is a

factor of more than 6 lower than the one determined in March (642 m3s-1; Tab. 1). In

order to validate these results by using the second approach discussed above, ET

rates are required. For central Sumatra ETs are not available, but can be calculated

by using the available precipitation rates and the determined water discharges (ET =

P - Qm). In March the calculated mean ET of 53% falls in the range of ETs

determined elsewhere in Indonesia (41-72%) (Kleinhans, 2004; Kumagai et al.,

2005). In September the calculated ET of 90% exceeds this range suggesting that

processes other than ET might also control the water discharge in the Siak. During

the September expedition it was observed that the upper part of the soil was dry in

regions which had been swamps with large areas of open water in March. One

explanation for a lower ground water level in September 2004 could be the low

precipitation in August (68-78 mm, Tab. 1, Fig. 2) which represents the driest month

in 2004. This low precipitation and an ET of 70% result in a water discharge of 99

m3s-1. Since this discharge equals the one which was measured in September and

the considered ET falls within the accepted range it is assumed that the enhanced

precipitation in September 2004 (194-231 mm) might have filled up the soil water

reservoir without changing the water discharge significantly. This in turn implies that

ETs varied between 53 and 70% during the wet and dry season in 2004.

DOC dynamics in the Siak

In order to investigate the spatial and temporal variability of DOC at selected stations

in the Siak and its tributaries samples were collected close to both riverbanks and the

centre as well as at different depths of the rivers. At sampling sites in the S. Tapung

Kanan (station 2/148) and the S. Tapung Kiri (station 147) the horizontal distribution

of DOC varies between 12-49% (Fig. 1a) indicating a poor mixing between waters at

the shallow river banks and the deeper parts of the headstreams. Downstream of

Pekanbaru (station 9 and 15) as well as in the underflow of the Mandau (station 8)

the river water was well mixed as indicated by a horizontal and vertical variability of

±5% and ±3%, respectively. Accordingly samples were taken along the Siak and the

Mandau in the centre of the river at a water depth of ~1m.


DOC concentrations ranged between 560 and 2,594 μmol l-1 (Fig. 3a). The

confluence of the headstreams S. Tapung Kanan and S. Tapung Kiri with mean DOC

concentrations of 1,551 and 605 μmol l-1, respectively, leads to a mean DOC

concentration in the Siak of 1,240 μmol l-1. A dramatic increase of DOC from station

9/114 to station 112 up- and downstream the Mandau junction indicates that the

Mandau contributes about half of the DOC entering the Siak estuary. In the Siak

estuary the DOC-poor, heavier brackish water is shifted below lighter DOC-enriched

river water. A linear relationship between decreasing DOC and increasing salinity in

the Siak estuary indicates a conservative mixing during the period of observation

(Fig. 3a, b; 4a).

Fig. 3: DOC (a) and Salinity (b) along the Siak in March 2004 (white circles) and September 2004 (black circles). Discharging DOC concentrations of the S. Tapung Kanan and Mandau are marked with white (March 2004) and black (September 2004) quadrangles and triangles.


According to the definition of Patel et al. (1999) the Mandau can be characterized as

a typical blackwater river because of its high DOC concentration, its dark brown-

colored, acidic water (pH 4.4 - 4.7) and its low concentration of TSM (12-41 mg l-1)

and POC (98-276 μmol l-1) compared to the Siak, which had higher pH values (5.2-

7.8), TSM (10-293 mg l-1) and POC concentrations (68-730 μmol l-1). Since even in

the Siak the POC falls much below the DOC concentrations and the contribution of

dissolved amino acid carbon to DOC is <1% (Meybeck, 1993; Dittmar et al., 2001) it

is assumed that autochthonous, phytoplankton-derived DOC hardly contributes to the

riverine DOC which appears to be mainly out of terrestrial origin.

Fig. 4: Salinity versus DOC concentrations measured in the Siak estuary in September 2004 (a) and peat soil coverages of the S. Tapung Kiri, S. Tapung Kanan and Mandau river basins versus DOC yields in March 2004 (black circles) and September 2004 (grey circles) (b).


DOC yields obtained for the three catchment basins of the Siak (S. Tapung Kiri, S.

Tapung Kanan and Mandau) tend to increase with an increasing proportional

coverage of peat soils and decreasing mean slopes in the catchment basins (Tab. 1,

Fig. 4b). This trend could be explained by an enhanced residence time of water due

to a lower topographic relief in the catchment basin and enhanced soil carbon

content both favouring leaching of DOC from soils (Ludwig et al., 1996; Dillon and

Molot, 1997; Hope et al., 1997b). High precipitation rates and subsequently

increased water discharges seem to enhance leaching from soils additionally as

indicated by DOC yields which are higher in March than in September (Tab. 1, Fig.

4b).

DOC export of the Siak

In order to estimate the DOC export of the Siak into the coastal ocean the DOC end-

member concentration derived from the linear relation between salinity and DOC was

multiplied by the freshwater discharge. In September a riverine DOC end-member

concentration of 2,195 μmol l-1 and a freshwater discharge of 99 m3s-1 suggest a

DOC export of 0.0069 Tg month-1. Due to a lack of DOC and salinity data for the Siak

estuary in March 2004 a DOC end-member concentration could not directly be

determined. However, since DOC concentrations in the Siak and Mandau were <15%

lower in March than in September, it is assumed that the mean riverine DOC

concentration also falls 15% below those determined in September. Considering

such a reduced DOC concentration (~1,866 μmol l-1) and the freshwater discharges

of 642 m3s-1 a DOC export of 0.038 Tg month-1 in March is suggested. As March and

September represent the wet and dry season, respectively, a monthly mean DOC

export of 0.0224 Tg month-1 (=0.27 Tg yr-1) is assumed to be representative for the

year 2004.

In order to validate this estimate a second approach is applied which is based on the

available precipitation rates and the estimated ETs (53 – 70%). The resulting annual

mean discharges vary between 1 and 1.6 * 1010 m3yr-1 and a mean DOC

concentration 2030 ±15% suggest a mean DOC flux of 0.32 Tg C yr-1. Considering

the uncertainties involved in both approaches the two different results reveal an

acceptable agreement so that an annual mean DOC discharge from the Siak into the


ocean of ~0.3 ± 0.03 Tg C yr-1 is assumed which places the Siak on position 17 on

the ranking list of DOC exports of major global rivers (Ludwig et al., 1996).

Estimated DOC export from peat draining Indonesian rivers

As observed from higher latitudes (Hope et al., 1997a; Aitkenhead et al., 1999) and

also seen in the Siak DOC yields strongly depend on the peat soil coverage within

the catchment basin and the water discharge (Fig. 4b). Approximately 10% of the

Indonesian landmass is covered by peat soils (Rieley et al., 1996a; FAO/UNESCO,

2003). Based on the observed relationship between peat soil coverage and DOC

yield of the Siak tributaries a peat soil coverage of 10% would imply DOC yields of

2.8 and 20 * 106 g yr-1 km-2 in August/September and March, respectively (Fig. 4b).

This difference is mainly caused by the water discharges which were low in

August/September and high in March. The associated precipitation rates varied

between 68-78 mm (August) and 297-351 mm (March), respectively (Tab. 1). The

annual mean precipitation rates over Indonesia (94° - 141° E, 11° S - 6° E) is 193

mm (GPCC, 2005). Such a precipitation rate suggests a DOC yield of 11 * 106 g yr-1

km-2 if linear interpolated between 2.8 and 20 * 106 g yr-1 km-2. Extrapolated over

entire Indonesia (~1.9*106 km2) this DOC yield suggests a DOC discharge of ~21 Tg

yr-1. This DOC export and the modelled Indonesian freshwater discharge of 4.26 *

1012 m3 yr-1 suggest furthermore a mean riverine DOC concentration of ~410 μmol l-1

which is at the lower range of estimated mean DOC concentrations of non-

Indonesian tropical rivers (408-667 μmol-1) (Meybeck, 1988; Ludwig et al., 1996).

Since Indonesia holds 48% of the tropical peat soils covering 10% of its land mass

and experiences one of the worlds highest precipitation rates it is assumed that this

estimate is an under- rather than an overestimate.

Conclusion The data obtained during the study suggest that leaching from peat soils is the main

source of DOC carried by the Siak and its tributaries. The DOC concentrations in the

Siak and its tributaries exceed those reported so far from other tropical rivers due to

effective leaching of DOC from the peat soils. The DOC yields increased with

enhanced precipitation indicating the sensitivity of peat soil leaching to changes in

the water discharge as also reported from higher latitudes (Tranvik and Jansson,

2002). In 2004 the annual mean DOC export from the Siak was estimated to be 0.3


Tg C yr-1. This contributes ~1.4% to the Indonesian DOC discharge which was

estimated to be ~21 Tg C yr-1. This of course is a first estimate which needs to be

validated in future by including data from further Indonesian rivers but it implies that

the small Indonesian rivers contribute at least 10% to the global riverine DOC

discharge into the ocean.

Acknowledgments We would like to thank all scientists and students from the University of Pekanbaru

who helped us during our field work. Furthermore, we would like to thank the rector of

the University of Riau and the captain of the research vessel R/V Senangin and his

crew for their support. Particularly, we would like to thank Venugopalan Ittekkot and

Günther Uher for their useful comments on the manuscript, Timo Ebenthal for his

support by the application of the ArcGIS program tools and our colleagues from the

ZMT for helpful discussions. We are also grateful to the Federal German Ministry for

Education, Science, Research and Technology (BMBF, Bonn) for financial support

(Grant No. 03F0392C-ZMT).


2.4. DOC discharges from the Indonesian blackwater river Siak and its estuary

into the Malacca Strait and their role as DOC source for the Indian Ocean

Antje Bauma, *, Tim Rixena, Herbert Siegelb, Thomas Pohlmannc, Joko Samiajid,

Christine Josed

aCenter for Tropical Marine Ecology, Fahrenheitstrasse 6, 28359 Bremen, Germany bBaltic Sea Research Institute Warnemünde, Seestrasse 15, 18119 Rostock, Germany cInstitute of Oceanography, Hamburg University, Bundesstrasse 53, 20146 Hamburg, Germany dUniversity of Riau, Jl. Simpang Panam Km 12.5, Pekanbaru, Riau, Indonesia

Marine Chemistry, submitted 11 June 2008

Abstract Three expeditions to the peat-draining river Siak in Central Sumatra (Indonesia) were

carried out between 2004 and 2006 to investigate sources and sinks of dissolved

organic carbon (DOC) in the river estuary and to quantify the DOC export into the

Malacca Strait. Incubation experiments upstream the estuary conducted in March

2006 showed that approximately 27% of the riverine DOC was degradable with a

half-life of 2 days whereas ~73% appear to be more refractory. Based on the

relationship between salinity and DOC two-point mixing analyzes were carried out to

quantify DOC inputs and losses in the estuary which catchment is largely covered by

peatsoils. The results indicate that especially during rainy periods, the Siak Estuary

acts as DOC source and nearly doubled the DOC discharge from the Siak River into

the Malacca Strait during the period of investigation. Satellite images reveal

pronounced plumes of the Siak and other peat-draining rivers in the Malacca Strait,

which strongly suggest that terrestrial DOC inputs increase the DOC concentration in

the Malacca Strait. Based on the difference between the DOC concentration

measured in the Malacca Strait and in its source water from the South China Sea, a

terrestrial DOC input from the Malacca Strait into the Indian Ocean of ~6.4 Tg yr-1

was estimated to which the Siak contributes ~8%. Thus the DOC export from the

Malacca Strait into the Indian Ocean is among the highest riverine DOC inputs into

the ocean reported world-wide.


Keywords: blackwater river, tropical peat, estuary, DOC export, Sumatra (Indonesia),

Malacca Strait

Introduction Photosynthesis of organic matter in the euphotic zone of the ocean, its subsequent

dissolution and downward mixing into the deep ocean, referred to as DOC export, is

considered to be the main source of the marine DOC pool, which holds with ~700 Gt

almost as much carbon as the atmosphere (~815 Gt) (Kurz, 1993; Hansell and

Carlson, 2002; Tans, 2008). Estimates of DOC exports (~1200 Tg C yr-1) exceed

those of DOC inputs from marine sediments (260 Tg C yr-1) and rivers (170-250 Tg C

yr-1) by one order of magnitude (Ludwig et al., 1996; Hansell and Carlson, 1998;

Cauwet, 2002; Harrison et al., 2005; Lahajnar et al., 2005). However, the high age of

marine DOC (1,300-6,200 years) suggests an enrichment of aged DOC released

from sediments and/or terrestrial soils (Williams and Druffel, 1987). Biomarker

studies indicated that only 0.7-2.4% of the marine DOC pool is of terrestrial origin

(Opsahl and Benner, 1997). Other authors point to analytical problems associated

with the separation between marine and terrestrial organic matter and suggest that

terrestrial DOC inputs and especially DOC outwelling from mangroves (20 Tg C yr-1)

could play an important role in the marine DOC cycle (Dittmar et al., 2006). DOC

inputs from the numerous small Indonesian rivers into the ocean were also

suggested to be as large as DOC inputs from mangroves world-wide (Baum et al.,

2007). Leaching from peatsoils, which correspond to ~10% of the Indonesian

landmass, is assumed to play a significant role as source of DOC in Indonesian

rivers. Large parts of the Indonesian peatsoils are located in coastal areas which

emphasizes the role of river estuaries as DOC source and/or sink in Central Sumatra,

Indonesia.

In a recent study the DOC export of the Siak into the coastal ocean for the year 2004

was calculated whereas the role of the river estuary was not investigated in detail

(Baum et al., 2007). In this work we will utilize the relationship between DOC and

salinity to quantify DOC sources and sinks in the Siak Estuary in order to estimate

the DOC export of the Siak into the coastal ocean for the period 2004-2006.

Furthermore, remote sensing data and results derived from numerical models were

evaluated to trace and quantify the riverine DOC discharge into the Malacca Strait

and further into the Indian Ocean.


Study area The Siak with a total length of 370 km and a catchment area of 11,500 km2 is one of

the major rivers draining the Central Sumatran lowlands. The Siak is located in the

province of Riau where it originates at the confluence of the two headstreams S.

Tapung Kanan and S. Tapung Kiri (S=Sungai). The Siak passes the province capital

Pekanbaru (100° 26’ E; 0° 32’ N, river km 180) and discharges into the Strait of

Bengkalis (Fig. 1). The major tributary of the Siak is the Mandau, with a sub-

catchment area of ~4000 km2. The source of the S. Tapung Kiri is located in the

highlands of Central Sumatra, while the S. Tapung Kanan as well as the Mandau

originate in peat-dominated lowlands and can be characterized as typical blackwater

rivers (Baum et al., 2007). The Siak river catchment is covered to ~45% with tropical

peatsoils. Peat swamp forests which formerly grow over the peat areas are to a large

extent converted into oilpalm- and rubber-estates (Laumonier, 1997).

Fig. 1: The investigated river Siak with the sampling stations of the expeditions in March and September 2004, July/August 2005 and March 2006 which are colored in black, white and grey circles, respectively. Areas covered by tropical peatsoils are colored in green.


Due to the meridional migration of the Intertropical Convergence Zone (ITCZ) dry and

wet seasons are not clearly pronounced. During our expedition to the Siak the

monthly rainfall ranged between 101 and 398 mm resulting in mean annual

freshwater discharges ranging between 1.23 and 1.89 * 1010 m3s-1 (Tab. 1). The

estuary of the Siak, defined as the mixing area of fresh and ocean water, is indicated

by salinities > 0.1 and ranges from the river mouth (river km 0) until river km ~300.

Methods Samplings for DOC, salinity and colored dissolved organic matter (CDOM) were

carried out in September 2004, July/August 2005 and March 2006. In 2004 and 2005

the entire Siak system including the headstreams S. Tapung Kanan and S. Tapung

Kiri as well as the Mandau were investigated while in 2006 the study was focused on

the Siak mainstream and the lower reaches of both headstreams. The coastal ocean

was sampled in 2005 and 2006 (Fig. 1).

DOC

Water samples were collected with a Niskin bottle and filtered through 0.45μm single-

use syringe filters into pre-combusted glass-ampoules. After acidification with

phosphoric acid the samples were stored cool. DOC samples were analyzed by

means of high temperature catalytic oxidation using a Dohrman DC-190 Total

Organic Carbon Analyzer equipped with a platinum catalyst. Before injection into the

furnace, the acidified samples were decarbonated by purging with oxygen. The

evolving CO2 was purified, dried and detected by a non-dispersive infrared detection

system. Calibration was carried out using potassium phthalate dissolved in MilliQ

water.

C-DOM, Salinity

For the determination of the C-DOM absorption water samples were filtered through

Whatman GF/F filters and measured at 440 nm (ay(440)) using a spectral photometer

PC-Spec. Salinity was directly measured with a WTW TetraCon 325_3 sensor and a

Sea-Bird SBE19plus.


DOC degradation experiments

DOC degradation experiments were conducted in March 2006. Water samples were

collected in the Siak mainstream after the confluence with the tributary Mandau (Fig.

1). Pre-combusted glass ampoules were filled with unfiltered Siak water and

incubated over a period of ~131 days under natural sunlight and constant

temperature (~32° C) in an artificial fish pond at the University of Riau (Pekanbaru).

Two samplings were done at the first day (4 and 8 hours after incubation) and one

sampling each at day 2 (after 29 hours), day 4 (after 76.5 hours) and day 9 (after 196

hours). After returning to Germany the remaining DOC ampoules were incubated

under UV light at constant temperatures (~32°C). The last sampling was conducted

after 131 days (3,148 hours). More detailed information can be found in Rixen et al.

(submitted).

Water discharge and DOC flux

Water discharges (Q) for the estimate of the DOC export into the ocean were

calculated based on the Siak catchment area and runoff, which is defined as the

difference between precipitation and evapotranspiration. Precipitation rates were

obtained from the 1 x 1° gridded global precipitation data set provided by the Global

Precipitation Climatology Centre (GPCC, 2005) (Baum et al., 2007).

Riverine DOC discharges were often quantified by multiplying freshwater discharges

with DOC concentrations. Selecting the right DOC concentration however is

problematic as the DOC concentrations often vary along the river and decrease in the

estuary due to mixing of DOC-rich river and DOC-poor ocean water. One approach

for deriving riverine DOC concentration is the correlation between salinity and DOC

(Alvarez-Salgado and Miller, 1998; Miller, 1999) whereby the DOC end-member

concentration is defined by the zero-intercept of the resulting regression equation

with the DOC axis. Although this is a reproducible method which has been also used

during our previous work (Baum et al., 2007) it ignores DOC inputs and

decomposition in river estuaries. Within this study, the linear relationship between

DOC and salinity is utilized to quantify DOC sources and sinks in the estuary and to

reassess the riverine DOC end-member concentration.


Satellite data

The application of satellite remote sensing methods was focused on the visible

spectral range due to the strong variations in water color. The application in the Siak

river discharge area requires high spatial resolution. Therefore, MODIS data with a

resolution of 250m provided by the Rapid Response System of NASA were used. For

local studies Landsat ETM+ data with a spatial resolution of 30m were implemented.

HAMSOM model

Results derived from a baroclinic, three-dimensional circulation model HAMSOM will

be presented in this study. HAMSOM was adapted to a fine-scale model domain

covering only the Siak estuary and its vicinity with a resolution of approximately 1 km.

In the vertical, the resolution was 2 m with the exception of the surface layer. The

model was run for 5.5 years covering a simulation period from January 2001 to May

2006. The latest development of HAMSOM was discussed in detail by Pohlmann

(2006). The model was forced by open boundary conditions including 8 tidal

constituents provided by a larger-scale HAMSOM application of the entire Malacca

Strait and western Java Sea, 6-hourly atmospheric data, and climatological means of

temperature and salinity.

Results and Discussion DOC in the Siak River and estuary

The DOC concentrations in the Siak and its tributaries ranged between 348 and 4043

μmol L-1 (Tab. 1). These concentrations exceed not only those of major global rivers

but also concentrations measured in other blackwater rivers world-wide (Hope et al.,

1994; Ludwig et al., 1996; Spencer et al., 2007). Riverine DOC end-member

concentrations (DOCcorrelation) derived from the correlation between salinity and DOC

ranged between 1613 and 2247 μmol L-1 and therefore suggest that DOC discharges

into ocean range between ~0.31 and 0.51 Tg C (mean 0.38 ± 0.1 Tg C). The highest

DOC discharges were observed in periods of enhanced rainfall, probably as a

consequence of increased peatsoil leaching (Tab. 1).


Tab. 1: Measured and calculated DOC concentrations (DOCx) and DOC discharges (FDOCx) as well as precipitation rates and freshwater discharges (Q) of the sampling campaigns in September 2004, July/August 2005 and March 2006.

September 2004 July/August 2005 March 2006

DOC [μmol L-1] min - max 408 – 3055 348 – 4043 537 – 1534

DOCcorrelation [μmol L-1] 2195 2247 1613

Q [* 1010 m3 s-1] 1.23 1.89 1.58

FDOC [Tg C yr-1] 0.33 0.51 0.31

Precipitation [mm] 199 304 254

Stationriver mouth (Fig. 1) 132 239 316

Salinitymeas 26.2 17.0 20.4

DOCmeas [μmol L-1] 560 1,916 687

a (percentage freshwater) 0.18 0.47 0.36

b (percentage ocean water) 0.82 0.53 0.64

DOCfresh_new(199) [μmol L-1] 2205 3851 1531

DOCfresh_new(70) [μmol L-1] 2793 3997 1784

FDOC_new(199) [Tg C yr-1] 0.33 0.87 0.29

FDOC_new(70) [Tg C yr-1] 0.41 0.91 0.34

In order to quantify possible sinks in the river estuary a DOC decomposition

experiment was carried out upstream the Siak Estuary (Fig. 1). The results of the

experiment showed that ~73% of the DOC appears to be refractory over a time scale

ranging somewhere between days and several months (Fig. 2). On the other hand

~27% of the DOC in the Siak can be degraded within two weeks suggesting a half-

life (T1/2) of the labile DOC of approximately 2 days (T1/2 = ln(2) / �; � = 0.016, see

Fig. 2). Such a short half-life implies that DOC decomposition in addition to mixing of

fresh and marine waters could play an important role for the decreasing DOC

concentrations in the estuary. Since a linear relationship between salinity and DOC

were observed during all samplings (Fig. 3) DOC inputs may compensate for DOC

decomposition in the Siak Estuary.


Fig. 2: DOC concentrations of Siak water which was incubated over a period of ~131 days under sunlight and constant temperature.

Fig. 3: Correlation between salinity and DOC in September 2004 (black circles), July/August 2005 (white circles) and March 2006 (grey circles).


DOC export

In order to quantify DOC sinks and sources in the Siak Estuary, new riverine DOC

end-member concentrations (DOCfresh_new) were calculated. For this purpose the

freshwater DOC concentration of the sampling stations that were located directly in

the river mouth were calculated by carrying out a salinity based two-point mixing

analysis.

Therefore, equation 1 was solved for DOCfresh_new while the proportions of river (a)

and ocean water (b) as well as the measured DOC concentrations (DOCmeas) were

taken from the sampling stations directly located at the Siak river mouth during each

expedition (stations 132, 239, 316; Fig. 1, Tab.1):

(DOCfresh_new) = (DOCmeas - (b * DOCcoastal))/a (Eq. 1)

‘a’ and ‘b’ were determined by solving the equations 2 and 3 for ‘a’ and ‘b’:

Salinitymeas= a * Salfresh + b * Salcoastal (Eq. 2)

a + b = 1 (Eq. 3)

where Salfresh is the salinity end-member of the river water (= 0) and Salcoastal the

salinity end-member of the ocean water (station 317, salinity = 32). Salinitymeas is the

salinity measured at each station.

As marine DOC end-member (DOCcoastal) a concentration of 198.64 μmol L-1 could be

used as it was the lowest DOC concentration measured in the Malacca Strait which

water body is a mixture of South China and Java Sea water as shown by model

simulations (Putri and Pohlmann, submitted). DOC concentrations of the Java Sea

are not available but DOC concentrations in the South China Sea are with 70 to 85

μmol L-1 (Hung et al., 2007) much lower than DOC concentrations measured in the

Malacca Strait. Since the Malacca Strait is strongly affected by river discharges as

will be discussed later, a DOC concentration of 70 μmol L-1 probably reflects a much

better marine DOC end-member concentration as the 198.64 μmol L-1 measured in

the Malacca Strait. However, in the following calculations we will first use the higher


and then the lower value in order to quantify DOC sources and sinks in the Siak

Estuary.

By using a coastal DOC end-member of 198.64 μmol L-1 the resulting new riverine

DOC end-member concentrations (DOCfresh_new(199)) were 0.5 and 71% higher in

September 2004 and July/August 2005, respectively, and 5% lower in March 2006

than the freshwater end-member concentrations (DOCcorrelation) derived from the

correlation between salinity and DOC (Tab. 1). Using a coastal end-member of 70

μmol L-1 results in new riverine DOC end-member concentrations (DOCfresh_new(70))

that are 27, 78 and 11% higher in September 2004, July/August 2005 and March

2006, respectively. Therefore, the Siak Estuary seems to act as DOC source in

July/August 2005 while in September 2004 and March 2006 the source function is

less pronounced. Since precipitation rates were highest in July/August 2005 it is

assumed that an increased leaching from peatsoils resulted in the new riverine DOC

end-member concentrations (DOCfresh_new(199) and DOCfresh_new(70)) that are 71-78%

higher than DOCcorrelation.

By using marine DOC end-member concentrations of 198.64 and 70 μmol L-1 DOC

discharges (FDOC_new(199) and FDOC_new(70)) result in 0.33, 0.87 and 0.29 Tg C yr-1

(mean 0.5 ± 0.3 Tg C yr-1) and 0.41, 0.91 and 0.34 Tg C yr-1 (mean 0.55 ± 0.3 Tg C

yr-1) for September 2004, July/August 2005 and March 2006, respectively, which

leads to a new DOC export that is on average ~32-48% higher compared to FDOC

(0.38 ± 0.1 Tg C yr-1).

Distribution of riverine DOC in the coastal ocean

The absorption (ay(440)) of colored dissolved organic substances (CDOM) which are

mainly soluble humic and fulvic acids derived from soil leaching and decomposition of

plant matter within the water body were measured in the Siak river system (Kirk,

1986). The highest CDOM absorbances were found in the S. Tapung Kanan (up to

18 m-1) and the Mandau (up to 26 m-1), which were up to six times higher than the

CDOM absorptions (ay(436)) measured in the Orinoco (Battin, 1998). The lowest

absorptions were observed in the S. Tapung Kiri (2.8 m-1) and in the Malacca Strait

(0.2 m-1).


Siegel et al. (submitted) showed that chlorophyll concentrations in the Siak varied

only slightly and therefore had no major influence on the spectral reflectance which

seemed to be controlled by the optical properties of total suspended matter (TSM)

and CDOM. CDOM correlates with DOC in the Siak (Fig. 4) and therefore allowed us

to trace the Siak river plume through the coastal ocean.

Fig. 4: Correlations between DOC and absorption coefficients at 440 nm (ay440) in September 2004 (black circles) and July/August 2005 (white circles).

The Landsat scene indicates that at flood tide southwards moving water from the

Malacca Strait pushes into the Bengkalis Strait and deflects the last outflow from the

Siak southwards into the Panjang Strait (Fig. 5a). There, the black water of the Siak

mixes with light brownish water which color indicates enhanced TSM concentrations

probably caused by resuspension of sediments in the extremely shallow Panjang

Strait. At this site, DOC possibly gets adsorbed to TSM (Cauwet, 2002) and

subsequently buried into sediments which could not be estimated so far. However,

during ebb tide the Siak river plume is advected north-westwards into the Malacca

Strait (Fig. 5b) which is also the general current direction of the residual flow as

indicated by model results. The latter also presents the net flow of the Siak discharge

which increases during the rainy season as shown by the model calculations. The

satellite images furthermore indicate dark plumes, probably caused by river


discharges from other peat-draining rivers to the north (Rokan) and south (Kampar)

of the Siak (Fig. 5b).

Fig. 5: Landsat 7 ETM+ scene acquired on 14th July 2002 11:10 SGT showing the Siak river plum during arising tide (a) adapted from Siegel et al. 2008. MODIS scene on 3rd January 2002 acquired 11:10 SGT showing the Siak discharge during flow off before low tide (b).

These pronounced river discharges into the Malacca Strait strongly support our

former assumption that the DOC concentration is influenced by terrestrial DOC inputs

which might have increased the concentration from 70 to 198.64 μmol L-1. This

increase of ~130 μmol L-1 in combination with a mean throughflow through the

Malacca Strait of 0.13 * 106 m3 s-1 (Humphries and Webb, 2007) would imply a mean

riverine DOC discharge into the Indian Ocean of 6.4 Tg C yr-1. Considering a mean

DOC export from the Siak of ~0.5 Tg C yr-1 in turn suggests that the Siak could

contribute ~8% to the terrestrial DOC discharge into the Indian Ocean through the

Malacca Strait.

Conclusions The results of this study indicate that the Siak Estuary acted as a DOC source during

rainy periods. On average DOC inputs into the estuary between 2004 and 2006

increased the DOC discharge from the Siak into the Malacca Strait by ~32-48%.

a) b)


Pronounced plumes of the Siak and other peat-draining rivers in the Malacca Strait,

which can be identified on satellite images, strongly suggest that further terrestrial

DOC inputs increase the DOC concentration in the Malacca Strait. The difference

between the DOC concentration measured in the Malacca Strait and in its source

water from the South China Sea of ~130 μmol L-1 implies a terrestrial DOC discharge

from the Malacca Strait into the Indian Ocean of ~6.4 Tg yr-1 to which the Siak

contributes ~8%. Thus, the Malacca Strait is after the rivers Amazon, Yangtze and

Zaire the fourth largest source of terrestrial DOC into the ocean world-wide which

strongly emphasizes the role of Indonesian peat-draining rivers as source for

terrestrial DOC inputs into the ocean.

Acknowledgements We are grateful to all students and scientists from the University of Riau (Pekanbaru,

Sumatra) for their help during the expeditions. For dedicated help during field and

laboratory work we would like to thank Csilla Kovacs. Furthermore, we would like to

thank Venugopalan Ittekkot for his useful comments on the manuscript and Esther

Borell for proofreading. We are also thankful for financial support through the Federal

German Ministry for Education, Science, Research and Technology (BMBF, Bonn)

(Grant No. 03F0392C-ZMT).

83

3. General conclusions

It was shown that the low nutrient concentrations measured in the Siak relative to

other rivers not only in Indonesia but world-wide may be attributed to leaching of

nutrient-poor peatlands. However an anthropogenically mediated increase in nutrient

concentrations, particularly in areas near cities, villages and industrial estates is

evident. In addition to domestic and industrial wastewater discharges the washout of

nitrogen fertilizers contributed significantly to the measured DIN concentrations in the

Siak. The comparison of nutrient data of the Siak and another peat-draining river in

South Sumatra, which was sampled prior to the main cultivation of oil palms in the

1970s, indicates that nutrient concentrations have increased in the Siak during the

last few decades.

Leaching of peatsoils was identified to be the major source of DOC in the Siak,

featuring concentrations that are among the highest reported world-wide. Leaching of

soils is assumed to be enhanced as a consequence of deforestation and drainage

activities in order to establish oil palm estates. However, such anthropogenic impacts

could not be quantified so far.

The decomposition of DOC was indicated to be the main factor controlling the

oxygen concentrations in the Siak. An increase in riverine DOC concentrations of

~15%, a likely result of enhanced soil leaching, would lead to anoxic conditions in the

river.

The DOC discharge of the Siak River into the estuary was calculated to be 0.38 ± 0.1

Tg C yr-1. Since the river estuary acts as additional DOC source, the DOC discharge

of the Siak into the coastal ocean accounts for 0.5 ± 0.3 Tg C yr-1. The DOC export of

the Siak and other peat-draining rivers increased the DOC concentration in the

Malacca Strait by ~130 μmol L-1 which results in a DOC flux ~6.4 Tg C yr-1 into the

Indian Ocean. Thus, the Malacca Strait presents after the Amazon, Yangtze and

Zaire the fourth largest contributor of terrestrial-derived DOC into the ocean. Based

on the DOC export of the Siak the annual DOC flux of Indonesian rivers was

extrapolated to be ~21 Tg C. Thus the DOC discharge of Indonesian rivers is

equivalent to the Amazon, the main contributor of terrestrial DOC (~26 Tg C yr-1)

84 General conclusions

(Ludwig et al., 1996), which underscores the relative importance of Indonesia in

terms of DOC input into the ocean.

85

4. Future perspectives

Problems that should be addressed in future studies in order to prove the results of

this thesis are briefly outlined below:

Verification of Indonesian riverine DOC export

The calculated DOC exports of Indonesian rivers and the Malacca Strait present the

first estimates of the contribution of Indonesia to the global DOC discharge into the

ocean so far. To specify these estimates, further Indonesian rivers should be

investigated in order to obtain additional data on the DOC export. Moreover, detailed

studies on the DOC dynamics in the Malacca Strait are needed.

Mixing of discharging blackwater with coastal waters that are enriched in suspended

matter may lead to the adsorption of DOC onto particles. If this is the case, coastal

oceans would act as a DOC sink where terrestrial DOC gets buried into sediments

rather than exported into the ocean. Possible trapping of DOC by suspended matter,

a potentially important process for the DOC export into the ocean, should be

therefore investigated in future campaigns.

Quantification of anthropogenic enhanced leaching

In order to quantify the anthropogenic impact on peatsoil leaching, comparative

studies should be carried out. Therefore blackwater rivers located in both disturbed

(drained, deforested, burned) and unaffected catchments should be investigated.

Although, the logistical realisation of such undertakings may be difficult, as oil palm

plantations, logging activities and fire clearance are spread over large scales in

Indonesia.

Investigation of further environmental consequences

The occurrence and extent of anoxic events in the Siak as well as their possible link

to periodic mass mortality of fish, which was observed downstream the city of

Pekanbaru, should be investigated during further expeditions.

Moreover, increased soil leaching and the aerobic decomposition of soil-carbon as a

consequence of intensive drainage lead to a destabilisation of peat and subsequent

86 Future perspectives

coastal erosion which may finally result in the loss of land and therefore has to be

quantified in the future.

As observed in March 2004, riverine nutrient concentrations were increased due to

fertilizers washed out of the soil. Due to the low abundance of primary producers in

the Siak, it is likely that substantial amounts of nutrients were transported into the

coastal ocean rather than being absorbed inside the river system. Thus the extent to

which high nutrient input causes eutrophic and even hypoxic conditions in the coastal

ocean should be investigated during further studies.

Lastly, consideration should be given to investigations addressing the effects of

climate change on the hydrological conditions and therefore the seasonalities in the

river system.

87

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App

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99

Mar

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Tap

ung

Kana

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2004

00

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,972

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,29

44,3

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- -

2 S.

Tap

ung

Kana

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2004

00

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,972

10

1° 1

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9 1

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54

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- 14

,23

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- -

2 S.

Tap

ung

Kana

n 14

.03.

2004

00

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,972

10

1° 1

2,28

9 1

- 5,

66

0,0

- 15

,11

38,2

2 -

- -

2 S.

Tap

ung

Kana

n 14

.03.

2004

00

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,972

10

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,02

124,

10

19,4

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7,29

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Tap

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n 14

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2004

00

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,972

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88

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9,34

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94

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Tap

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2004

00

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52

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38

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8,81

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05

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01

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19,6

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10,3

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8,38

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55

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04

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33,6

01

101°

03,

903

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0 -

26,1

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5,39

12

,27

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88

4,74

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Tap

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6,9

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83

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8,61

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40

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Tap

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04

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01

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0 -

28,7

5 16

2,82

15

,46

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35

4,42

3 S.

Tap

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Kiri

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04

00°

33,6

01

101°

03,

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0 -

29,7

1 13

6,22

14

,53

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11

5,36

3 S.

Tap

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Kiri

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04

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33,6

01

101°

03,

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1 -

6,76

0,

0 -

19,6

6 12

9,39

15

,10

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47

4,29

4 M

anda

u 17

.03.

2004

01

° 03

,977

10

1° 1

6,35

6 1

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02

0,0

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58

114,

98

11,7

3 -2

7,84

6,

72

4 M

anda

u 17

.03.

2004

01

° 03

,977

10

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6,35

6 1

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89

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36

107,

36

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53

4 M

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u 17

.03.

2004

01

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10

1° 1

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6 1

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95

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44

3,77

4 M

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u 17

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2004

01

° 03

,977

10

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6,35

6 1

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86

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05

18,5

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8,28

2,

89

4 M

anda

u 17

.03.

2004

01

° 03

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10

1° 1

6,35

6 1

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19

0,0

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95

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8,53

5,

45

4 M

anda

u 17

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2004

01

° 03

,977

10

1° 1

6,35

6 2,

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6,16

0,

0 -

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76

5 Si

ak

17.0

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04

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75,0

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5 Si

ak

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04

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13

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5 Si

ak

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04

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1 28

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0 35

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13

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95

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5 Si

ak

17.0

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04

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6 -

6,11

0,

0 -

42,1

3 33

3,13

11

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- 4,

96

6 Si

ak

17.0

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04

- -

1 28

,2

5,17

0,

0 -

48,0

3 22

7,64

15

,18

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99

3,36

6 Si

ak

17.0

3.20

04

- -

2 28

,4

5,25

0,

0 -

38,4

6 -

- -

-

7 M

anda

u 22

.03.

2004

00

° 48

,420

10

1° 4

5,25

7 8

28,2

4,

92

0,0

- 12

,33

- -

-29,

43

2,72

7 M

anda

u 22

.03.

2004

00

° 48

,420

10

1° 4

5,25

7 6

30

4,46

0,

0 -

12,1

5 -

- -

-

7 M

anda

u 22

.03.

2004

00

° 48

,420

10

1° 4

5,25

7 1

28,8

4,

43

0,0

0,40

11

,73

- -

-29,

66

2,87

8 M

anda

u 22

.03.

2004

00

° 50

,190

10

1° 4

0,58

7 8

29,9

4,

55

0,0

- 7,

63

- -

-28,

94

-1,0

9

8 M

anda

u 22

.03.

2004

00

° 50

,190

10

1° 4

0,58

7 0

29,3

4,

53

0,0

0,45

6,

30

- -

-29,

33

8,62

100

App

endi

x

Stat

ion

Riv

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Dat

e Po

sitio

n N

Po

sitio

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[m]

Tem

p. [°

C]

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ity

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] TS

M [m

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] PO

C [μ

m L

-1]

Cor

g/N

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org

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9 Si

ak

22.0

3.20

04

00°

42,7

98

101°

40,

172

14

29,5

5,

98

0,0

- 45

,56

193,

58

16,7

4 -2

8,44

2,

25

9 Si

ak

22.0

3.20

04

00°

42,7

98

101°

40,

172

7 29

,3

6,16

0,

0 -

40,8

9 23

5,80

14

,91

-27,

48

5,28

9 Si

ak

22.0

3.20

04

00°

42,7

98

101°

40,

172

1 29

,6

6,24

0,

0 0,

35

47,9

7 19

5,15

13

,29

-28,

29

4,87

10

Siak

23

.03.

2004

00

° 32

,300

10

1° 2

6,75

0 1

28,6

-

0,0

- 29

,40

- -

-28,

21

3,46

10

Siak

23

.03.

2004

00

° 32

,300

10

1° 2

6,75

0 1

28,5

-

0,0

- 30

,97

131,

78

17,5

4 -2

9,00

4,

93

10

Siak

23

.03.

2004

00

° 32

,300

10

1° 2

6,75

0 1

28,6

-

0,0

- 28

,37

131,

19

16,0

8 -2

8,63

2,

51

11

Siak

23

.03.

2004

00

° 34

,450

10

1° 3

2,90

0 1

28,9

-

0,0

- 33

,23

134,

53

11,9

2 -2

8,76

4,

63

11

Siak

23

.03.

2004

00

° 34

,450

10

1° 3

2,90

0 1

28,9

-

0,0

- 37

,00

138,

63

11,9

7 -2

8,81

3,

71

11

Siak

23

.03.

2004

00

° 34

,450

10

1° 3

2,90

0 1

29,2

-

0,0

- 50

,86

216,

01

17,1

1 -2

8,55

4,

01

12

Siak

23

.03.

2004

00

° 35

,800

10

1° 3

4,75

0 1

28,9

-

0,0

- 37

,11

- -

- -

12

Siak

23

.03.

2004

00

° 35

,800

10

1° 3

4,75

0 1

28,9

-

0,0

- 27

,29

130,

11

12,3

6 -2

8,50

4,

45

12

Siak

23

.03.

2004

00

° 35

,800

10

1° 3

4,75

0 1

28,9

-

0,0

- 26

,60

102,

36

13,8

1 -2

8,63

3,

57

13

Siak

23

.03.

2004

00

° 37

,100

10

1° 3

6,00

0 1

29,5

-

0,0

- 58

,26

240,

50

14,1

7 -2

8,61

4,

82

13

Siak

23

.03.

2004

00

° 37

,100

10

1° 3

6,00

0 1

29

- 0,

0 -

25,3

1 12

8,32

12

,03

-28,

75

-

13

Siak

23

.03.

2004

00

° 37

,100

10

1° 3

6,00

0 1

28,9

-

0,0

- 36

,80

142,

59

13,3

6 -

-

14

Siak

23

.03.

2004

00

° 38

,450

10

1° 3

7,00

0 1

29,4

-

0,0

- 21

,36

24,0

1 3,

29

-28,

62

-11,

33

15

Siak

24

.03.

2004

00

° 32

,483

10

1° 2

6,22

4 5

29

5,06

0,

0 -

18,0

0 11

4,24

12

,71

-28,

39

4,92

15

Siak

24

.03.

2004

00

° 32

,483

10

1° 2

6,22

4 9

29,6

5,

67

0,0

- 21

,80

117,

65

16,6

1 -2

8,36

6,

50

15

Siak

24

.03.

2004

00

° 32

,483

10

1° 2

6,22

4 1

29,3

5,

69

0,0

- 15

,03

96,6

6 16

,48

-28,

59

6,61

15

Siak

24

.03.

2004

00

° 32

,483

10

1° 2

6,22

4 1

29,8

5,

78

0,0

- 15

,73

94,5

8 12

,73

-28,

68

5,87

15

Siak

24

.03.

2004

00

° 32

,483

10

1° 2

6,22

4 1

29,8

5,

76

0,0

- 25

,55

165,

41

17,3

4 -2

8,66

6,

37

16

S. T

apun

g Ki

ri 24

.03.

2004

00

° 35

,841

10

1° 1

8,53

6 0,

5 31

,2

6,36

0,

0 -

18,7

0 12

3,23

16

,43

-28,

79

7,16

17

S. T

apun

g Ka

nan

24.0

3.20

04

00°

36,5

53

101°

19,

017

1 30

,4

5,25

0,

0 -

10,2

4 93

,56

12,5

1 -2

8,78

5,

95

17

S. T

apun

g Ka

nan

24.0

3.20

04

00°

36,5

53

101°

19,

017

5 30

,6

5,25

0,

0 -

11,3

3 11

5,62

18

,33

-29,

05

4,00

18

Siak

24

.03.

2004

00

° 35

,605

10

1° 1

9,01

7 1

30,8

5,

35

0,0

- 17

,00

124,

95

18,2

3 -

3,02

18

Siak

24

.03.

2004

00

° 35

,605

10

1° 1

9,01

7 5

31,1

5,

55

0,0

- 20

,43

128,

66

11,2

2 -2

8,84

6,

15

19

Siak

24

.03.

2004

00

° 33

,540

10

1° 2

2,96

3 1

31,2

5,

68

0,0

- 9,

88

84,4

5 17

,39

-28,

31

9,67

19

Siak

24

.03.

2004

00

° 33

,540

10

1° 2

2,96

3 1

30,7

5,

6 0,

0 -

- -

- -

-

*SD

= S

ampl

ing

dept

h

App

endi

x

1

01

Stat

ion

Riv

er

O2

[mg

L-1]

DO

C [μ

mol

L-1]

AA

-DO

C [%

] PO

43- [μ

mol

L-1

] N

O3- [μ

mol

L-1

] N

O2- [μ

mol

L-1

] N

H4+ [μ

mol

L-1]

DIN

[μm

ol L

-1]

1 Ka

mpa

r -

- -

0,74

21

,91

0,13

5,

24

27,2

8

1 Ka

mpa

r -

- -

0,15

22

,50

0,13

3,

21

25,8

4

1 Ka

mpa

r -

302,

45

- 0,

34

25,1

7 0,

22

3,20

28

,58

1 Ka

mpa

r -

242,

32

- 0,

11

22,2

5 0,

14

2,80

25

,19

1 Ka

mpa

r -

- -

0,09

21

,71

0,10

2,

68

24,4

9

2 S.

Tap

ung

Kana

n -

- -

1,22

34

,93

0,10

4,

69

39,7

2

2 S.

Tap

ung

Kana

n -

1823

,09

0,66

0,

98

34,2

7 0,

08

4,10

38

,46

2 S.

Tap

ung

Kana

n -

- -

0,74

35

,83

0,35

4,

71

40,8

9

2 S.

Tap

ung

Kana

n -

859,

19

- 1,

10

35,5

0 0,

14

5,37

41

,01

2 S.

Tap

ung

Kana

n -

- -

1,10

35

,02

0,13

5,

19

40,3

4

2 S.

Tap

ung

Kana

n -

- -

1,10

35

,50

0,12

5,

12

40,7

5

3 S.

Tap

ung

Kiri

- -

- 0,

52

53,5

2 0,

59

6,85

60

,96

3 S.

Tap

ung

Kiri

- -

- 0,

74

54,0

7 0,

56

3,95

58

,58

3 S.

Tap

ung

Kiri

- -

- 0,

41

53,1

7 0,

53

4,85

58

,55

3 S.

Tap

ung

Kiri

- -

- 0,

52

52,9

7 0,

50

5,28

58

,75

3 S.

Tap

ung

Kiri

- -

- 0,

60

53,4

0 0,

64

5,58

59

,62

3 S.

Tap

ung

Kiri

- -

- 0,

51

53,3

2 0,

54

7,63

61

,49

4 M

anda

u -

2270

,37

0,38

-

- -

- -

4 M

anda

u -

2048

,19

- -

- -

- -

5 Si

ak

2,6

- -

- -

- -

-

5 Si

ak

2 -

- -

- -

- -

5 Si

ak

2,2

- -

- -

- -

-

6 Si

ak

1,4

- -

- -

- -

-

7 M

anda

u 0,

9 36

17,0

7 -

0,52

3,

99

0,00

3,

66

7,65

7 M

anda

u 0,

8 -

- 0,

69

3,85

0,

01

4,95

8,

81

7 M

anda

u 1

- -

0,50

3,

66

0,00

4,

04

7,71

8 M

anda

u 1,

5 30

07,1

3 -

1,05

2,

65

0,00

2,

27

4,92

8 M

anda

u 1,

1 29

16,4

8 -

0,69

2,

49

0,00

4,

25

6,74

9 Si

ak

2,1

1172

,08

- 0,

47

50,2

3 0,

44

10,5

4 61

,21

9 Si

ak

1,6

- -

0,44

50

,95

0,47

10

,84

62,2

5

9 Si

ak

2,1

1043

,59

- 0,

27

50,9

0 0,

44

8,48

59

,82

102

A

ppen

dix

Stat

ion

Riv

er

O2

[mg

L-1]

DO

C [μ

mol

L-1]

AA

-DO

C [%

] PO

43- [μ

mol

L-1

] N

O3- [μ

mol

L-1

] N

O2- [μ

mol

L-1

] N

H4+ [μ

mol

L-1]

DIN

[μm

ol L

-1]

10

Siak

-

- -

1,10

53

,55

0,39

13

,53

67,4

8

10

Siak

-

1565

,51

0,57

0,

82

53,4

4 0,

18

5,95

59

,57

10

Siak

-

- -

0,88

53

,86

0,23

6,

51

60,6

1

11

Siak

-

- -

0,96

58

,63

0,36

7,

65

66,6

3

11

Siak

-

1112

,62

- 0,

99

58,1

0 0,

33

9,77

68

,20

11

Siak

-

- -

0,43

54

,82

0,37

5,

33

60,5

2

12

Siak

-

- -

0,37

53

,47

0,34

12

,51

66,3

1

12

Siak

-

- -

0,86

56

,21

0,37

4,

98

61,5

7

12

Siak

-

- -

0,14

43

,48

0,44

1,

95

45,8

6

13

Siak

-

- -

0,28

49

,33

0,30

3,

92

53,5

5

13

Siak

-

- -

0,14

45

,44

0,14

4,

63

50,2

0

13

Siak

-

- -

0,36

50

,21

0,31

5,

80

56,3

2

14

Siak

-

- -

0,62

50

,97

0,14

4,

83

55,9

3

14

Siak

-

- -

- -

- -

-

14

Siak

-

- -

- -

- -

-

15

Siak

2,

1 -

- 1,

10

38,8

2 0,

16

5,32

44

,29

15

Siak

2,

2 12

90,8

5 0,

74

1,22

38

,42

0,11

6,

81

45,3

4

15

Siak

1,

9 13

42,6

1 1,

24

1,03

37

,37

0,04

4,

80

42,2

1

15

Siak

-

1272

,72

- 36

,71

36,4

4 0,

00

47,7

9 84

,23

15

Siak

-

- -

6,33

36

,29

0,01

9,

77

46,0

7

16

S. T

apun

g Ki

ri 4,

5 66

6,95

-

4,34

38

,88

0,24

10

,00

49,1

3

17

S. T

apun

g Ka

nan

1,9

1701

,74

0,81

5,

42

18,1

7 0,

03

9,51

27

,71

17

S. T

apun

g Ka

nan

1,7

- -

5,06

15

,45

0,02

7,

30

22,7

7

18

Siak

2,

1 13

66,1

7 -

1,05

25

,81

0,06

5,

72

31,5

9

18

Siak

2,

4 -

- 0,

88

25,5

7 0,

07

5,82

31

,46

19

Siak

3,

6 14

08,8

0 -

0,86

26

,65

0,16

5,

24

32,0

4

19

Siak

3,

2 -

- -

- -

- -

App

endi

x

1

03

Sept

embe

r 200

4

Stat

ion

Riv

er

Dat

e Po

sitio

n N

Po

sitio

n E

*SD

[m]

Tem

p. (°

C)

pH

Salin

ity

Secc

hi [m

]TS

M [m

g L-1

] PO

C [μ

m L

-1]

Cor

g/N

�13C

org

�15N

101

S.Ta

pung

kana

n 24

.09.

2004

00

° 36

´ 40,

7´´

101°

19´

05,

5´´

1 32

,8

7,04

0,0

- -

- -

- -

101

S.Ta

pung

kana

n 24

.09.

2004

00

° 36

´ 40,

7´´

101°

19´

05,

5´´

3 30

,6

6,50

0,0

- -

- -

- -

102

S.Ta

pung

Kiri

24

.09.

2004

00

° 35

´ 46,

5´´

101°

18´

34,

5´´

1 31

,8

7,17

0,0

- -

- -

- -

103

S.Ta

pung

Kiri

24

.09.

2004

00

° 35

´ 46,

5´´

101°

18´

34,

5´´

1 -

6,10

0,0

- -

- -

- -

104

Siak

24

.09.

2004

00

° 35

´ 55,

3´´

101°

19´

30,

4´´

1 31

,7

6,50

0,0

- -

- -

- -

105

Siak

24

.09.

2004

00

° 33

´ 32,

9´´

101°

22´

59,

7´´

1 27

,87

6,65

0,0

- -

- -

- -

106

Man

dau

24.0

9.20

04

01°

04´ 0

1,1´

´ 10

1° 1

6´ 1

3,4´

´ 0,

2 29

6,

870,

0 -

40,3

8 25

4,46

21

,29

-29,

2 5,

4

107

Rok

an

24.0

9.20

04

01°

37´ 1

6,7´

´ 10

1° 2

0´ 0

3,8´

´ 1

- -

0,0

- 7,

09

182,

49

54,2

5 -3

0,4

-

108

Dum

ai

24.0

9.20

04

01°

39´ 3

5,7´

´ 10

1° 2

6´ 2

8,4´

´ 1

- -

0,0

- 7,

56

99,7

2 27

,34

-27,

7 -

109

Siak

25

.09.

2004

00

° 32

´ 31,

0´´

101°

26´

07,

1´´

1 29

,4

6,82

0,0

0,40

28

,30

111,

98

16,2

2 -2

9,0

-

110

Siak

25

.09.

2004

00

° 32

´ 55,

9´´

101°

25´

23,

3´´

1 29

,9

6,87

0,0

0,40

31

,05

126,

02

17,1

7 -2

8,8

-

111

Man

dau

25.0

9.20

04

00°

50´ 1

1,4´

´ 10

1° 4

0´ 3

5,2´

´ 1

30

4,58

0,0

0,25

26

,32

276,

40

15,6

9 -2

9,4

-

112

Siak

25

.09.

2004

00

° 46

´ 09,

4´´

101°

47´

12,

1´´

1 30

,8

6,83

0,0

0,25

38

,12

245,

57

14,5

2 -2

9,1

-

113

Siak

25

.09.

2004

00

° 45

´ 21,

5´´

101°

42´

32,

1´´

1 31

7,

130,

0 0,

25

39,8

0 22

2,55

12

,55

-28,

5 1,

5

114

Siak

25

.09.

2004

00

° 42

´ 41,

9´´

101°

40´

06,

3´´

1 32

6,

980,

0 0,

25

57,1

6 25

9,94

9,

82

-28,

5 3,

3

115

Siak

25

.09.

2004

00

° 35

´ 50,

8´´

101°

35´

19,

1´´

1 31

,3

- 0,

0 -

- -

- -

-

116

Siak

25

.09.

2004

00

° 34

´ 29,

8´´

101°

31´

59,

8´´

1 30

,8

6,60

0,0

0,25

44

,92

163,

59

10,3

4 -2

8,1

0,3

117

S. T

apun

g Ki

ri 26

.09.

2004

00

° 35

´ 46,

6´´

100°

39´

04,

4´´

1 28

-

0,0

- 9,

72

68,3

3 16

,50

- -

118

Kam

par

26.0

9.20

04

00°

18´ 0

8,1´

´ 10

0° 5

4´ 8

2,9´

´ 1

- -

0,0

- -

- -

- -

119

Kam

par

26.0

9.20

04

00°

18´ 0

8,1´

´ 10

0° 5

4´ 8

2,9´

´ 1

- -

0,0

- -

- -

- -

120

Kam

par

26.0

9.20

04

00°

18´ 0

8,1´

´ 10

0° 5

4´ 8

2,9´

´ 1

- -

0,0

- 6,

86

90,6

1 14

,37

- -

124

Estu

ar

28.0

9.20

04

01°

15´ 3

2,2´

´ 10

2° 1

0´ 0

1,4´

´ 1

- 7,

89-

0,35

65

,70

96,5

2 21

,67

-27,

0 5,

4

124

Estu

ar

28.0

9.20

04

01°

15´ 3

2,2´

´ 10

2° 1

0´ 0

1,4´

´ 3

- 7,

89-

0,35

94

,45

139,

39

21,0

8 -2

7,1

3,2

125

Estu

ar

28.0

9.20

04

01°

14´ 0

0,9´

´ 10

2° 1

1´ 5

8,7´

´ 1

- 7,

9327

,4

0,50

35

,63

43,3

8 25

,10

-26,

6 2,

8

125

Estu

ar

28.0

9.20

04

01°

14´ 0

0,9´

´ 10

2° 1

1´ 5

8,7´

´ 10

-

7,98

27,9

0,

50

71,6

6 72

,73

22,1

2 -2

7,2

3,4

126

Estu

ar

28.0

9.20

04

01°

15´ 3

4,7´

´ 10

2° 1

0´ 1

5,2´

´ 1

- 7,

8325

,3

0,25

11

8,60

20

0,16

19

,69

-27,

7 4,

2

126

Estu

ar

28.0

9.20

04

01°

15´ 3

4,7´

´ 10

2° 1

0´ 1

5,2´

´ 7

- 7,

8927

,1

0,25

46

4,20

68

1,76

15

,39

-27,

3 3,

3

127

Estu

ar

28.0

9.20

04

01°

15´ 3

4,7´

´ 10

2° 1

0´ 1

5,2´

´ 1

31,2

7,

5319

,1

0,25

79

,60

204,

92

23,3

7 -2

7,8

4,3

128

Estu

ar

28.0

9.20

04

01°

13´ 5

9,9´

´ 10

2° 1

1´ 5

9,5´

´ 1

- 7,

9027

,6

0,40

78

,69

107,

71

19,1

0 -2

7,4

8,9

104

A

ppen

dix

Stat

ion

Riv

er

Dat

e Po

sitio

n N

Po

sitio

n E

*SD

[m]

Tem

p. (°

C)

pH

Salin

ity

Secc

hi [m

]TS

M [m

g L-1

] PO

C [μ

m L

-1]

Cor

g/N

�13C

org

�15N

128

Estu

ar

28.0

9.20

04

01°

13´ 5

9,9´

´ 10

2° 1

1´ 5

9,5´

´ 10

-

7,90

27,5

0,

40

449,

52

678,

74

12,3

9 -2

7,6

3,5

129

Estu

ar

28.0

9.20

04

01°

14´ 4

7,9´

´ 10

2° 1

1´ 0

4,2´

´ 1

- 6,

9012

,2

- -

- -

- -

130

Estu

ar

28.0

9.20

04

01°

15´ 3

3,9´

´ 10

2° 1

0´ 1

3,5´

´ 1

- 7,

6020

,8

0,40

47

,96

93,2

9 30

,40

-28,

0 4,

1

130

Estu

ar

28.0

9.20

04

01°

15´ 3

3,9´

´ 10

2° 1

0´ 1

3,5´

´ 7

- 7,

8627

,5

0,40

88

,04

138,

97

14,4

7 -2

7,6

4,8

131

Estu

ar

29.0

9.20

04

01°

20´ 8

5,0´

´ 10

2° 0

9´ 6

2,9´

´ 1

- 7,

9127

,8

0,40

92

,26

139,

34

19,5

3 -2

6,9

4,7

132

Estu

ar

29.0

9.20

04

01°

14´ 2

9,7´

´ 10

2° 1

0´ 1

0,0´

´ 1

- 7,

8026

,2

0,35

68

,37

91,8

5 20

,70

-27,

3 4,

2

133

Estu

ar

29.0

9.20

04

01°

13´ 2

1,2´

´ 10

2° 1

0´ 0

4,3´

´ 1

- 7,

8026

,3

0,50

54

,15

64,1

8 21

,27

-27,

2 3,

7

134

Siak

29

.09.

2004

01

° 07

´ 54,

8´´

102°

09´

37,

6´´

1 -

6,88

10,9

0,

25

50,2

9 10

9,39

20

,19

-28,

2 3,

3

135

Siak

29

.09.

2004

01

° 12

´ 06,

1´´

102°

09´

56,

5´´

1 -

7,34

18,6

0,

20

127,

77

247,

08

23,1

3 -2

8,2

3,2

136

Siak

29

.09.

2004

01

° 10

´ 18,

7´´

102°

09´

21,

7´´

1 -

6,93

12,6

0,

20

131,

16

301,

99

16,4

6 -2

8,2

2,6

137

Siak

29

.09.

2004

01

° 07

´ 50,

7´´

102°

09´

09,

0´´

1 29

,9

6,31

5,0

0,15

26

3,20

64

5,84

16

,50

-28,

4 1,

7

138

Siak

29

.09.

2004

01

° 07

´ 04,

1´´

102°

07´

11,

0´´

1 29

,9

6,33

3,4

0,10

29

0,52

73

0,48

18

,85

-28,

6 1,

3

139

Siak

29

.09.

2004

01

° 04

´ 36,

5´´

102°

07´

57,

5´´

1 29

,8

6,10

1,3

0,10

14

1,40

38

7,46

15

,04

-28,

5 2,

6

140

Siak

30

.09.

2004

01

° 07

´ 43,

3´´

102°

07´

47,

8´´

1 29

,6

6,22

3,0

0,15

12

0,68

33

3,27

17

,62

-28,

6 3,

9

141

Siak

30

.09.

2004

01

° 03

´ 26,

3´´

102°

07´

02,

7´´

1 29

,7

6,19

1,6

0,15

20

7,76

53

9,66

15

,73

-28,

1 2,

4

142

Siak

30

.09.

2004

102°

05´

26,

6´´

1 28

,4

6,03

0,7

0,10

14

6,84

41

3,14

16

,25

-28,

8 1,

1

143

Siak

30

.09.

2004

01

° 00

´ 23,

2´´

102°

06´

32,

8´´

1 29

,7

6,05

0,1

0,10

17

9,64

49

2,36

15

,00

-28,

6 0,

9

144

Siak

30

.09.

2004

00

° 53

´ 56,

3´´

102°

02´

50,

3´´

1 30

,2

6,13

0,0

0,15

84

,52

291,

07

14,5

7 -2

8,9

4,0

145

Siak

30

.09.

2004

00

° 50

´ 23,

7´´

102°

03´

03,

9´´

1 -

6,23

0,0

0,15

56

,84

234,

06

13,1

0 -2

9,0

14,4

145

Siak

30

.09.

2004

00

° 50

´ 23,

7´´

102°

03´

03,

9´´

12

29,9

6,

400,

0 -

- -

- -

-

147

S. T

apun

g Ki

ri 02

.10.

2004

00

° 33

´ 38,

5´´

101°

03´

53,

5´´

1 -

6,92

0,0

0,60

31

,03

116,

16

10,4

7 -2

9,2

3,6

148

S. T

apun

g Ka

nan

02.1

0.20

04

00°

44´ 5

6,0´

´ 10

1° 1

2´17

,5´´

1

29,8

4 -

0,0

0,25

47

,96

187,

83

10,2

1 -2

6,2

4,6

*SD

= S

ampl

ing

dept

h

App

endi

x

1

05

Stat

ion

Riv

er

O2

[mg

L-1]

DO

C [μ

mol

L-1]

AA

-DO

C [%

] PO

43- [μ

mol

L-1

] N

O3- [μ

mol

L-1]

NO

2- [μm

ol L

-1]

NH

4+ [μm

ol L

-1]

DIN

[μm

ol L

-1]

101

S.Ta

pung

kana

n 2,

1 -

- -

- -

- -

101

S.Ta

pung

kana

n 2,

3 -

- -

- -

- -

102

S.Ta

pung

Kiri

-

- 1,

71

- -

- -

-

103

S.Ta

pung

Kiri

-

- 1,

71

- -

- -

-

104

Siak

4,

1 -

- -

- -

- -

105

Siak

2,

4 -

- -

- -

- -

106

Man

dau

5,6

1938

,92

0,58

2,

15

13,5

7 0,

37

1,59

15

,53

107

Rok

an

- 48

27,7

5 0,

23

3,77

5,

67

1,09

2,

57

9,32

108

Dum

ai

- 45

93,0

1 -

1,59

0,

00

1,13

1,

22

2,35

109

Siak

3,

7 10

08,0

1 -

7,82

12

,89

1,00

5,

35

19,2

5

110

Siak

3,

7 10

70,5

6 -

6,18

13

,86

1,04

5,

34

20,2

5

111

Man

dau

1,7

3054

,88

0,29

15

,39

24,1

0 0,

22

3,75

28

,06

112

Siak

1,

4 24

39,6

2 -

2,79

9,

17

2,17

10

,35

21,6

9

113

Siak

1

1877

,82

- 2,

19

6,00

7,

32

15,8

3 29

,15

114

Siak

1,

06

1379

,79

- 80

,33

12,0

0 12

,19

13,0

4 37

,24

115

Siak

-

- -

- -

- -

-

116

Siak

-

1082

,02

- 11

,35

15,6

6 4,

19

13,4

8 33

,33

117

S. T

apun

g Ki

ri -

677,

2 -

- -

- -

-

118

Kam

par

2 -

- -

- -

- -

119

Kam

par

2,1

- -

- -

- -

-

120

Kam

par

2,2

- -

- -

- -

-

124

Estu

ar

4,9

2238

,38

- 6,

97

7,21

0,

26

0,94

8,

41

124

Estu

ar

4,9

565,

31

- 3,

66

7,06

0,

11

0,89

8,

06

125

Estu

ar

4,5

637,

67

- 3,

08

7,03

0,

22

0,32

7,

57

125

Estu

ar

4,3

407,

63

- 1,

40

5,95

0,

37

0,13

6,

45

126

Estu

ar

4,4

675,

48

- 1,

51

8,75

1,

19

0,25

10

,20

126

Estu

ar

4 54

6,42

-

2,01

7,

91

0,37

0,

00

8,28

127

Estu

ar

- 11

42,7

4 -

2,86

14

,54

1,28

0,

13

15,9

6

128

Estu

ar

4,9

- -

1,22

7,

00

0,15

0,

00

7,15

128

Estu

ar

- 73

4,24

-

1,53

7,

12

0,09

0,

07

7,27

130

Estu

ar

4,5

990,

99

- 1,

48

14,7

4 1,

56

0,44

16

,74

106

A

ppen

dix

Stat

ion

Riv

er

O2

[mg

L-1]

DO

C [μ

mol

L-1]

AA

-DO

C [%

] PO

43- [μ

mol

L-1

] N

O3- [μ

mol

L-1]

NO

2- [μm

ol L

-1]

NH

4+ [μm

ol L

-1]

DIN

[μm

ol L

-1]

130

Estu

ar

3,8

1935

,24

- 2,

52

8,64

0,

22

0,00

8,

86

131

Estu

ar

4,5

- -

- -

- -

-

132

Estu

ar

4,8

559,

7 -

1,90

7,

50

0,85

0,

77

9,11

133

Estu

ar

5,1

- -

1,18

7,

42

0,43

0,

03

7,89

134

Siak

3

- -

197,

43

24,4

7 0,

17

0,00

24

,64

135

Siak

3,

8 10

62,7

-

89,0

4 18

,78

0,96

0,

00

19,7

4

136

Siak

3

1414

,82

- 3,

23

26,6

7 0,

69

0,12

27

,49

137

Siak

2,

2 20

77,6

1 -

2,44

31

,18

0,89

0,

86

32,9

4

138

Siak

1,

9 19

26,8

5 -

4,47

35

,71

0,48

0,

61

36,8

0

139

Siak

1,

5 19

68,5

7 0,

41

3,60

36

,76

0,15

0,

30

37,2

0

140

Siak

2

2107

,89

- 2,

32

34,7

1 1,

15

0,16

36

,03

141

Siak

1,

6 20

18,9

3 -

2,63

32

,34

0,32

0,

65

33,3

1

142

Siak

1,

3 20

82,2

6

1,73

25

,79

0,00

0,

00

25,7

9

143

Siak

1,

3 22

64,8

7 0,

40

2,52

34

,42

0,00

0,

00

34,4

2

144

Siak

0,

8 25

39,8

5 -

118,

14

29,4

5 0,

22

0,30

29

,97

145

Siak

0,

65

2513

,89

- 2,

61

27,3

0 0,

06

0,83

28

,19

147

S. T

apun

g Ki

ri 5,

1 55

5,05

1,

36

1,26

23

,51

1,28

2,

37

27,1

6

148

S. T

apun

g Ka

nan

4,2

1718

,61

- 2,

12

55,5

8 0,

02

7,22

62

,82

App

endi

x

1

07

July

/Aug

ust 2

005

Stat

ion

Riv

er

Dat

e Po

sitio

n N

Po

sitio

n E

*SD

[m]

Tem

p. (°

C)

pH

Salin

ity

Secc

hi [m

] TS

M [m

g L-1

] PO

C [μ

m L

-1]

Cor

g/N

�13C

org

�15N

201

S. T

apun

g Ka

nan

16.0

7.20

05

00°

38, 1

61

101°

18,

803

1

28,3

4,

890,

0 -

1148

,73

- -

-30,

2 3,

6

202

S. T

apun

g Ka

nan

16.0

7.20

05

00°

44, 3

14

101°

14,

355

1

28,9

5,

440,

0 -

34,1

4 18

9,15

16

,57

-29,

7 7,

4

203

S. T

apun

g Ka

nan

16.0

7.20

05

00°

42, 8

53

101°

15,

375

1

29,3

5,

890,

0 -

42,8

7 19

8,68

19

,74

-29,

6 5,

9

204

S. T

apun

g Ka

nan

16.0

7.20

05

00°

40, 3

59

101°

17,

357

1

29,4

5,

920,

0 -

46,7

1 16

8,51

14

,00

-29,

2 3,

3

205

S. T

apun

g Ka

nan

16.0

7.20

05

00°

36, 7

96

101°

18,

990

1

28,7

5,

600,

0 -

166,

72

277,

31

13,6

6 -2

9,0

0,8

206

Siak

16

.07.

2005

00

° 32

, 899

10

1° 4

3, 0

17

1 29

,3

6,10

0,0

- -

- -

- -

208

S. T

apun

g Ki

ri 16

.07.

2005

00

° 33

, 321

10

1° 2

3, 8

95

1 28

,8

5,49

0,0

- 11

5,76

25

4,39

15

,74

-29,

3 2,

7

209

S. T

apun

g Ki

ri 17

.07.

2005

00

° 36

, 219

10

1° 1

3, 5

38

0,5

27,8

6,

160,

0 -

63,7

0 21

0,82

12

,10

-29,

1 3,

8

210

S. T

apun

g Ki

ri 17

.07.

2005

00

° 36

, 063

10

1° 1

8, 5

82

1 28

,3

5,55

0,0

- 76

,34

274,

98

14,9

2 -2

9,2

3,5

211

Siak

17

.07.

2005

00

° 34

, 886

10

1° 2

0, 3

87

1 28

,9

6,10

0,0

- 67

,13

178,

69

11,9

1 -2

9,4

6,6

212

Siak

17

.07.

2005

00

° 32

, 986

10

1° 2

5, 3

39

1 29

,4

5,69

0,0

- 48

,55

180,

84

18,4

1 -

5,1

213

Man

dau

19.0

7.20

05

00°

58, 8

68

101°

27,

876

1

28,1

4,

860,

0 0,

35

14,2

2 -

- -2

9,9

5,4

214

Man

dau

19.0

7.20

05

00°

53, 0

95

101°

38,

085

1

28,4

4,

300,

0 -

18,2

0 20

0,58

18

,63

-29,

6 4,

1

215

Man

dau

19.0

7.20

05

00°

50, 1

81

101°

40,

590

1

28,2

4,

040,

0 0,

25

17,6

0 21

4,72

22

,07

-29,

9 3,

3

216

Siak

19

.07.

2005

00

° 46

, 675

10

1° 4

6, 3

64

1 29

,1

5,78

0,0

- 31

,92

137,

62

14,5

3 -

1,1

217

Siak

19

.07.

2005

00

° 42

, 263

10

1° 3

9, 6

78

- 28

,8

5,85

0,0

- 70

,22

231,

86

16,4

9 -2

8,7

-0,5

218

Siak

19

.07.

2005

00

° 32

, 770

10

1° 2

8, 1

61

- 28

,5

5,51

0,0

- 45

,10

188,

84

11,6

0 -2

7,92

4,

7

219

S. T

apun

g Ka

nan

21.0

7.20

05

00°

44, 9

66

101°

12,

291

1

28,7

6,

090,

0 0,

27

41,8

8 22

3,62

15

,86

-29,

79

4,6

220

Man

dau

21.0

7.20

05

01°

02, 2

20

101°

15,

987

-

29,9

3,

770,

0 0,

40

11,3

7 20

3,08

20

,03

-30,

48

4,6

221

S. T

apun

g Ki

ri 23

.07.

2005

00

° 33

, 265

10

1° 1

6, 3

63

1 28

3,

800,

0 0,

30

4,62

12

1,83

26

,12

-29,

46

3,5

222

S. T

apun

g Ki

ri 23

.07.

2005

00

° 33

, 642

10

1° 0

3, 8

92

2,4

29,6

6,

390,

0 0,

40

20,1

6 86

,26

10,9

1 -3

0,05

4,

3

223

S. T

apun

g Ki

ri 23

.07.

2005

00

° 35

´ 46,

6´´

100°

39´

04,

4´´

- 28

,9

6,36

0,0

- 12

,69

77,4

4 9,

42

-27,

20

6,6

229

Mal

akka

-Stra

ße

26.0

7.20

05

01°

53, 4

97

102°

00,

395

1

- 8,

0832

,0

4,00

2,

99

10,8

2 10

,17

-26,

25

1,8

230

Beng

kalis

27

.07.

2005

01

° 20

, 675

10

2° 1

1, 4

05

1 29

,3

7,80

27,7

0,

50

35,9

6 55

,50

13,9

1 -2

7,73

3,

5

231

Beng

kalis

27

.07.

2005

01

° 12

, 650

10

2° 1

3, 9

30

1 30

,2

7,50

22,5

0,

55

18,8

6 45

,75

18,6

0 -2

7,63

4,

2

232

Beng

kalis

27

.07.

2005

01

° 03

, 835

10

2° 1

3, 7

48

1 30

,2

7,60

28,0

0,

30

170,

82

286,

89

18,5

1 -2

7,62

4,

0

233

Beng

kalis

27

.07.

2005

01

° 26

, 590

10

2° 0

6, 1

40

1 30

,5

7,91

30,0

2,

00

4,98

12

,58

10,0

7 -2

5,94

-

239

Siak

28

.07.

2005

01

° 14

, 177

10

2° 0

9, 9

03

1 30

,41

6,66

17,0

0,

30

23,8

0 12

1,87

20

,08

-28,

67

3,3

108

A

ppen

dix

Stat

ion

Riv

er

Dat

e Po

sitio

n N

Po

sitio

n E

*SD

[m]

Tem

p. (°

C)

pH

Salin

ity

Secc

hi [m

] TS

M [m

g L-1

] PO

C [μ

m L

-1]

Cor

g/N

�13C

org

�15N

240

Siak

28

.07.

2005

01

° 11

, 600

10

2° 0

9, 8

50

1 31

,29

6,51

10,8

-

32,3

4 12

8,79

16

,65

-28,

58

-

241

Siak

28

.07.

2005

01

° 07

, 920

10

2° 0

8, 6

20

1 30

,85

5,66

2,5

0,07

15

0,56

45

3,74

16

,91

-28,

87

0,9

242

Siak

28

.07.

2005

01

° 07

, 280

10

2° 0

7, 1

68

1 30

,1

5,57

1,8

0,08

16

7,80

60

3,66

19

,99

-28,

87

1,4

243

Siak

28

.07.

2005

01

° 04

, 940

10

2° 0

7, 8

42

1 30

,1

5,21

0,2

0,03

41

0,65

14

61,6

3 24

,60

-29,

01

1,3

244

Siak

28

.07.

2005

01

° 02

, 350

10

2° 0

4, 8

30

1 29

,48

4,90

0,0

0,07

20

1,90

62

5,67

20

,33

-28,

90

1,4

245

Siak

28

.07.

2005

00

° 59

, 037

10

2° 0

6, 0

66

1 29

,48

4,54

0,0

0,10

94

,13

441,

69

20,5

5 -2

9,01

1,

4

252

Siak

28

.07.

2005

01

° 11

, 820

10

2° 0

9, 8

20

1 -

6,95

- 0,

40

24,3

8 92

,95

10,2

0 -2

8,85

5,

1

253

Siak

28

.07.

2005

01

° 25

, 113

10

2° 0

9, 8

11

1 -

7,70

- -

- -

- -

-

254

Siak

29

.07.

2005

01

° 21

, 000

10

2° 0

9, 7

29

1 29

,58

7,01

26,2

0,

45

14,0

8 57

,85

15,4

4 -2

8,41

4,

8

255

Siak

29

.07.

2005

01

° 13

, 740

10

2° 1

0, 1

03

1 30

,1

6,45

9,5

- -

- -

- -

256

Siak

29

.07.

2005

01

° 09

, 088

10

2° 0

9, 7

16

1 30

,4

5,46

1,7

- -

- -

- -

257

Siak

29

.07.

2005

01

° 07

, 890

10

2° 0

7, 9

40

1 30

,1

5,17

0,5

0,05

22

1,76

81

3,40

18

,83

- 1,

2

258

Siak

29

.07.

2005

01

° 04

, 431

10

2° 0

7, 8

61

1 29

,9

5,07

0,0

- -

- -

- -

259

Siak

29

.07.

2005

01

° 02

, 353

10

2° 0

5, 0

49

1 30

,6

5,17

0,0

0,12

71

,08

312,

68

17,9

6 -2

9,06

0,

8

260

Siak

29

.07.

2005

00

° 55

, 500

10

2° 0

5, 1

20

1 30

5,

190,

0 0,

20

73,9

5 33

2,33

17

,73

-29,

29

1,4

261

Siak

29

.07.

2005

00

° 49

, 893

10

2° 0

3, 4

71

1 29

,2

5,00

0,0

0,13

79

,05

293,

91

17,6

4 -2

8,98

3,

1

265

Beng

kalis

- D

umai

29

.07.

2005

01

° 27

, 820

10

2° 0

5, 4

50

1 -

7,84

- 1,

00

129,

72

216,

59

16,4

0 -2

7,74

5,

0

266

Beng

kalis

- D

umai

29

.07.

2005

01

° 31

, 240

10

1° 5

9, 9

30

1 -

7,85

- 1,

80

5,70

23

,53

10,5

7 -2

6,23

4,

7

267

Beng

kalis

- D

umai

29

.07.

2005

01

° 37

, 380

10

1° 5

3, 9

90

1 -

8,01

- 2,

00

5,64

15

,35

8,91

-2

5,33

3,

5

270

Siak

01

.08.

2005

00

° 32

, 598

10

1° 2

6, 1

02

1 28

,6

6,19

- -

- -

- -

-

271

Siak

01

.08.

2005

00

° 32

, 486

10

1° 2

6, 2

28

1 28

,5

5,40

0,0

- 58

,57

162,

00

11,6

8 -

4,1

273

Siak

01

.08.

2005

00

° 47

, 784

10

1° 5

5, 4

05

1 29

,8

4,88

0,0

0,10

46

,96

267,

18

14,3

7 -2

9,17

3,

7

274

Siak

01

.08.

2005

00

° 46

, 772

10

1° 4

6, 0

13

1 30

5,

590,

0 0,

25

31,5

0 16

0,69

15

,87

-28,

80

3,8

275

Siak

01

.08.

2005

00

° 46

, 918

10

1° 4

5, 1

23

1 29

,5

5,90

- 0,

25

33,2

6 15

6,06

15

,00

-29,

04

4,0

276

Siak

01

.08.

2005

00

° 42

, 271

10

1° 3

9, 6

79

1 29

,5

6,05

0,0

- -

- -

- -

277

Siak

01

.08.

2005

00

° 37

, 757

10

1° 3

6, 3

28

1 28

,9

5,56

0,0

0,15

80

,37

199,

86

12,8

9 -2

8,28

2,

3

278

Siak

01

.08.

2005

00

° 32

, 767

10

1° 2

8, 1

32

1 29

,4

5,50

- -

- -

- -

-

*SD

= S

ampl

ing

dept

h

App

endi

x

1

09

Stat

ion

Riv

er

O2

[mg

L-1]

DO

C [μ

mol

L-1]

PO43-

[μm

ol L

-1]

NO

3- [μm

ol L

-1]

NO

2- [μm

ol L

-1]

NH

4+ [μm

ol L

-1]

DIN

[μm

ol L

-1]

201

S. T

apun

g Ka

nan

- 17

98,7

3 2,

52

40,9

5 0,

23

12,7

7 53

,96

202

S. T

apun

g Ka

nan

3,4

1514

,18

3,69

31

,71

0,17

3,

52

35,4

0

203

S. T

apun

g Ka

nan

3,3

1482

,17

3,72

28

,04

0,06

3,

97

32,0

7

204

S. T

apun

g Ka

nan

3,6

1255

,11

3,04

25

,19

0,05

4,

02

29,2

6

205

S. T

apun

g Ka

nan

3,9

1035

,89

1,14

41

,53

0,08

4,

34

45,9

5

208

S. T

apun

g Ki

ri 3,

3 12

98,9

6 4,

47

25,8

9 0,

09

3,29

29

,27

209

S. T

apun

g Ki

ri 4,

4 59

2,59

0,

98

45,0

1 0,

19

1,15

46

,34

210

S. T

apun

g Ki

ri 4,

4 93

6,83

2,

49

42,6

3 0,

06

2,64

45

,33

211

Siak

3,

8 83

0,21

0,

00

12,5

3 0,

11

0,37

13

,00

212

Siak

3,

5 11

23,1

1 2,

15

20,8

2 0,

03

2,60

23

,45

213

Man

dau

2,4

2207

,53

2,09

6,

63

0,16

1,

69

8,49

214

Man

dau

2,4

2020

,87

1,56

7,

43

0,07

2,

54

10,0

4

215

Man

dau

2,2

1308

,47

1,45

8,

48

0,06

2,

92

11,4

6

216

Siak

1,

3 13

07,7

9 0,

93

17,2

2 0,

10

7,71

25

,03

217

Siak

1,

8 11

82,8

5 1,

50

23,4

2 0,

03

7,48

30

,92

218

Siak

-

1274

,73

5,26

33

,11

0,06

2,

76

35,9

3

219

S. T

apun

g Ka

nan

3,5

1308

,47

2,92

21

,22

0,02

3,

71

24,9

6

220

Man

dau

3,2

4166

,93

13,8

9 2,

25

0,51

2,

34

5,11

221

S. T

apun

g Ki

ri 2,

3 10

93,5

8 20

,57

- -

- 2,

28

222

S. T

apun

g Ki

ri 5,

5 45

1,65

2,

98

22,6

8 0,

17

1,83

24

,68

223

S. T

apun

g Ki

ri 5,

4 34

8,05

4,

42

26,6

9 0,

25

2,59

29

,52

229

Mal

akka

-Stra

ße

4,8

1058

,36

0,06

0,

62

0,24

4,

31

5,17

230

Beng

kalis

4,

6 10

93,5

8 0,

50

6,01

0,

08

3,80

9,

89

231

Beng

kalis

4,

1 11

41,3

7 0,

36

6,88

0,

14

1,83

8,

85

232

Beng

kalis

4,

6 10

02,6

1 0,

47

4,96

0,

06

2,20

7,

23

233

Beng

kalis

5,

7 10

71,8

7 0,

21

2,94

0,

05

1,00

4,

00

239

Siak

3,

3 19

15,9

3 0,

54

8,27

0,

18

2,33

10

,77

240

Siak

2,

8 -

0,62

9,

77

0,24

2,

84

12,8

5

241

Siak

1,

2 21

94,9

3 3,

33

15,4

8 0,

29

3,58

19

,35

242

Siak

0,

7 22

97,9

3 0,

87

17,8

0 0,

30

1,95

20

,04

243

Siak

0,

4 -

1,24

22

,82

0,31

0,

62

23,7

4

110

A

ppen

dix

Stat

ion

Riv

er

O2

[mg

L-1]

DO

C [μ

mol

L-1]

PO43-

[μm

ol L

-1]

NO

3- [μm

ol L

-1]

NO

2- [μm

ol L

-1]

NH

4+ [μm

ol L

-1]

DIN

[μm

ol L

-1]

244

Siak

0,

4 -

1,26

23

,77

0,20

3,

69

27,6

6

245

Siak

0,

8 18

33,7

7 1,

44

19,6

2 0,

13

6,78

26

,53

250

Siak

Kec

il 1,

4 83

0,21

0,

29

10,6

0 0,

18

1,92

12

,70

251

Siak

Kec

il M

ündu

ng

3,7

1574

,35

0,30

3,

51

0,09

3,

37

6,97

252

Siak

2,

9 15

74,3

5 0,

34

8,52

0,

15

1,95

10

,62

254

Siak

4,

5 14

11,2

5 0,

38

6,79

0,

22

4,64

11

,64

257

Siak

0,

8 19

93,8

5 1,

05

23,3

0 0,

36

2,70

26

,36

259

Siak

1,

15

- 1,

44

20,0

8 0,

14

5,68

25

,90

260

Siak

1,

3 17

07,9

5 4,

32

17,3

1 0,

25

7,76

25

,32

261

Siak

1,

3 11

58,0

1 1,

68

17,2

1 0,

11

6,39

23

,71

265

Beng

kalis

- D

umai

-

- 0,

30

4,63

0,

08

2,42

7,

13

266

Beng

kalis

- D

umai

4,

8 11

25,1

0 0,

24

2,36

0,

12

3,99

6,

47

267

Beng

kalis

- D

umai

5,

4 10

17,0

6 0,

12

1,03

0,

36

2,08

3,

47

271

Siak

3,

4 10

17,3

1 -

- -

- -

273

Siak

1,

2 19

15,9

3 1,

58

- 0,

14

6,78

-

274

Siak

1,

4 15

84,7

8 1,

08

- 0,

08

6,13

-

275

Siak

1,

1 13

54,3

2 -

-

- -

276

Siak

1,

1 -

- -

- -

-

277

Siak

2,

9 -

2,38

-

0,08

9,

73

-

278

Siak

3,

4 -

- -

- -

-

App

endi

x

1

11

Mar

ch 2

006

Stat

ion

Riv

er

Dat

e Po

sitio

n N

Po

sitio

n E

*SD

[m]

Tem

p. (°

C)

pH

Salin

ity

Secc

hi [m

]TS

M [m

g L-1

] PO

C [μ

m L

-1]

Cor

g/N

�13C

org

�15N

301

Siak

25

.03.

2006

00

° 76

, 267

10

1° 7

9, 4

75

1 29

,3

5,76

0,

0 -

- -

- -

-

302

Siak

25

.03.

2006

00

° 67

, 301

10

1° 6

3, 7

39

1 -

- -

- -

- -

- -

303

Siak

28

.03.

2006

00

° 32

, 353

10

1° 2

6, 8

50

1 29

,5

5,30

0,

0 -

- -

- -

- 30

4 Si

ak

28.0

3.20

06

00°

36, 7

29

101°

35,

674

1

29,5

5,

51

0,0

0,25

20

,10

90,0

6 15

,99

-28,

04

3,85

304

Siak

28

.03.

2006

00

° 36

, 729

10

1° 3

5, 6

74

1 -

- -

30

,07

151,

57

18,7

3 -2

9,27

5,

18

305

Siak

28

.03.

2006

00

° 42

, 684

10

1° 4

0, 1

22

1 29

,8

5,91

0,

0 0,

23

41,7

5 21

0,50

14

,39

-28,

91

3,16

305

Siak

28

.03.

2006

00

° 42

, 684

10

1° 4

0, 1

22

1 -

- -

32

,58

193,

00

17,1

0 -2

8,32

3,

14

306

Siak

28

.03.

2006

00

° 45

, 914

10

1° 4

7, 5

48

1 29

,8

5,70

0,

0 0,

25

35,6

3 21

1,80

17

,74

-29,

12

3,26

306

Siak

28

.03.

2006

00

° 45

, 914

10

1° 4

7, 5

48

1 -

- -

41

,32

194,

07

16,7

5 -2

9,00

3,

64

307

Siak

28

.03.

2006

00

° 49

, 771

10

2° 0

3, 5

66

1 30

,5

5,79

0,

0 0,

23

43,4

6 18

8,28

17

,64

-28,

79

3,69

307

Siak

28

.03.

2006

00

° 49

, 771

10

2° 0

3, 5

66

1 -

- -

38

,89

192,

72

18,8

5 -2

8,71

3,

21

308

Siak

28

.03.

2006

00

° 59

, 876

10

2° 0

6, 4

88

1 31

,0

5,84

0,

2 0,

15

72,7

8 30

6,91

16

,76

-29,

01

-0,6

3

308

Siak

28

.03.

2006

00

° 59

, 876

10

2° 0

6, 4

88

1 -

- -

- 71

,30

324,

52

20,6

2 -2

8,74

5,

06

309

Siak

28

.03.

2006

01

° 02

, 669

10

2° 0

4, 5

08

1 30

,8

5,97

1,

9 -

- -

- -

-

310

Siak

28

.03.

2006

01

° 05

, 229

10

2° 0

7, 3

54

1 31

,0

6,11

4,

1 -

- -

- -

-

311

Siak

28

.03.

2006

01

° 07

, 033

10

2° 0

7, 2

72

1 30

,1

6,30

5,

7 -

- -

- -

-

312

Siak

28

.03.

2006

01

° 07

, 608

10

2° 0

8, 5

08

1 30

,6

6,46

7,

0 0,

12

59,5

4 18

3,84

21

,85

-28,

13

5,12

312

Siak

28

.03.

2006

01

° 07

, 608

10

2° 0

8, 5

08

1 -

- -

- 60

,52

183,

88

19,7

1 -2

8,04

-

313

Siak

28

.03.

2006

01

° 09

, 645

10

2° 0

9, 3

04

1 30

,9

6,61

10

,4

- -

- -

- -

314

Siak

28

.03.

2006

01

° 11

, 576

10

2° 0

9, 8

66

1 30

,6

7,08

16

,8

0,15

59

,64

165,

89

21,1

4 -2

8,15

5,

25

314

Siak

28

.03.

2006

01

° 11

, 576

10

2° 0

9, 8

66

1 -

- -

- 66

,83

167,

53

16,9

8 -2

7,91

4,

85

315

Siak

28

.03.

2006

01

° 14

, 254

10

2° 0

9, 8

18

1 30

,1

7,40

22

,0

- -

- -

- -

316

Siak

28

.03.

2006

01

° 14

, 506

10

2° 1

0, 2

45

1 30

,7

7,45

20

,4

0,20

47

,90

121,

84

15,8

9 -2

8,01

4,

47

316

Siak

28

.03.

2006

01

° 14

, 506

10

2° 1

0, 2

45

1 -

- -

- 47

,98

122,

96

11,5

8 -2

7,47

5,

62

317

Mal

acca

Stra

it 30

.03.

2006

01

° 53

, 576

10

2° 0

0, 4

10

1 -

8,11

-

- 3,

21

14,4

7 9,

26

-24,

07

1,89

317

Mal

acca

Stra

it 30

.03.

2006

01

° 53

, 576

10

2° 0

0, 4

10

1 -

- -

- 4,

74

12,3

2 7,

01

-24,

92

4,68

318

Mal

acca

Stra

it 30

.03.

2006

01

° 53

, 906

10

2° 0

0, 5

60

1 -

8,11

-

- 9,

88

19,0

4 8,

92

-23,

25

5,94

318

Mal

acca

Stra

it 30

.03.

2006

01

° 53

, 906

10

2° 0

0, 5

60

1 -

- -

- 10

,58

19,0

6 10

,23

-23,

70

4,35

112

A

ppen

dix

Stat

ion

Riv

er

Dat

e Po

sitio

n N

Po

sitio

n E

*SD

[m]

Tem

p. (°

C)

pH

Salin

ity

Secc

hi [m

]TS

M [m

g L-1

] PO

C [μ

m L

-1]

Cor

g/N

�13C

org

�15N

319

Mal

acca

Stra

it 30

.03.

2006

01

° 54

, 307

10

1° 5

5, 6

02

1 -

8,09

-

- 3,

64

20,1

8 11

,82

-25,

27

4,07

319

Mal

acca

Stra

it 30

.03.

2006

01

° 54

, 307

10

1° 5

5, 6

02

1 -

- -

- 5,

57

25,0

6 11

,46

-24,

39

6,21

320

Mal

acca

Stra

it 30

.03.

2006

01

° 54

, 081

10

1° 5

0, 9

27

1 -

7,97

-

- 12

,02

42,2

1 9,

86

-22,

56

3,97

320

Mal

acca

Stra

it 30

.03.

2006

01

° 54

, 081

10

1° 5

0, 9

27

1 -

- -

- 9,

49

29,4

8 9,

82

-23,

58

6,11

321

Mal

acca

Stra

it 30

.03.

2006

01

° 53

, 991

10

1° 4

7, 4

76

1 -

7,17

-

- 45

,75

78,9

7 11

,40

-24,

95

5,56

321

Mal

acca

Stra

it 30

.03.

2006

01

° 53

, 991

10

1° 4

7, 4

76

1 -

- -

- 32

,25

60,4

4 13

,16

-25,

26

6,00

354

S. T

apun

g Ki

ri 06

.04.

2006

00

° 35

´ 46,

5´´

101°

18´

34,

5´´

1 30

,2

6,03

0,

0 -

- -

- -

-

355

Siak

06

.04.

2006

00

° 35

´ 55,

3´´

101°

19´

30,

4´´

1 33

,7

5,64

0,

0 -

- -

- -

-

356

S. T

apun

g Ka

nan

06.0

4.20

06

00°

36´ 4

0,7´

´ 10

1° 1

9´ 0

5,5´

´ 1

30,6

5,

46

0,0

- -

- -

- -

360

Siak

29

.03.

2006

00

° 35

,120

10

1° 2

8,48

9 1

- -

- -

17,9

8 23

1,80

11

,10

-28,

71

4,84

360

Siak

29

.03.

2006

00

° 35

,120

10

1° 2

8,48

9 1

- -

- -

19,1

9 26

4,93

14

,54

-28,

79

4,54

361

Siak

29

.03.

2006

00

° 35

,034

10

1° 2

8,88

0 1

- -

- -

18,6

4 24

4,05

11

,98

-28,

13

4,74

361

Siak

29

.03.

2006

00

° 35

,034

10

1° 2

8,88

0 1

- -

- -

17,2

2 23

5,15

13

,94

-28,

17

4,69

362

S. T

apun

g Ka

nan

30.0

3.20

06

00°

37,0

95

101°

19,

135

1 -

5,22

-

- -

- -

- -

363

S. T

apun

g Ka

nan

30.0

3.20

06

00°

36,1

80

101°

18,

836

1 -

5,72

-

- -

- -

- -

364

S. T

apun

g Ki

ri 30

.03.

2006

00

° 35

,675

10

1° 1

7,45

3 1

- 5,

48

- -

- -

- -

-

365

S. T

apun

g Ki

ri 30

.03.

2006

00

° 36

,025

10

1° 1

8,81

9 1

- 6,

42

- -

- -

- -

-

366

Siak

30

.03.

2006

00

° 35

,566

10

1° 1

9,80

3 1

- 6,

44

- -

- -

- -

-

367

Siak

30

.03.

2006

00

° 34

,838

10

1° 2

0,40

2 1

- 6,

06

- -

- -

- -

-

368

Siak

30

.03.

2006

00

° 33

,938

10

1° 2

1,28

9 1

- 5,

70

- -

- -

- -

-

*SD

= S

ampl

ing

dept

h

App

endi

x

1

13

Stat

ion

Riv

er

O2

[mg

L-1]

DO

C [μ

mol

L-1

] PO

43- [μ

mol

L-1

] N

O3- [μ

mol

L-1]

NO

2- [μm

ol L

-1]

NH

4+ [μm

ol L

-1]

DIN

[μm

ol L

-1]

301

Siak

1,

1 -

- -

- -

-

302

Siak

1,

3 -

- -

- -

-

303

Siak

3,

7 -

1,95

16

,44

0,09

2,

08

18,6

1

304

Siak

3,

4 11

66,9

7 2,

36

22,3

3 0,

08

6,19

28

,60

305

Siak

1,

0 12

11,6

9 0,

55

31,1

5 0,

15

7,68

38

,98

306

Siak

0,

9 14

04,6

8 1,

62

20,5

1 0,

19

12,4

6 33

,16

307

Siak

1,

1 15

45,9

0 1,

92

25,7

7 0,

11

10,7

6 36

,64

308

Siak

1,

2 16

44,2

6 0,

87

28,0

7 0,

20

1,84

30

,12

309

Siak

1,

3 -

0,25

29

,52

0,34

1,

30

31,1

6

310

Siak

-

- 1,

15

30,3

5 0,

77

1,57

32

,69

311

Siak

-

- 0,

68

29,3

9 1,

08

1,31

31

,78

312

Siak

3,

7 15

34,2

8 0,

23

29,2

4 1,

09

0,97

31

,30

313

Siak

-

- 0,

28

25,8

3 0,

99

1,71

28

,53

314

Siak

3,

2 82

7,44

1,

03

20,1

8 0,

84

0,79

21

,82

315

Siak

-

- 0,

24

14,3

4 0,

61

0,86

15

,80

316

Siak

4,

4 67

8,16

0,

25

15,0

7 0,

61

0,96

16

,65

317

Mal

acca

Stra

it -

198,

64

- -

- -

-

318

Mal

acca

Stra

it -

326,

83

-0,6

9 -0

,76

-0,0

2 -

-0,7

8

319

Mal

acca

Stra

it -

272,

16

-0,6

3 -0

,31

0,11

-

-0,2

1

320

Mal

acca

Stra

it -

251,

93

-0,4

5 -0

,53

0,03

-

-0,5

0

321

Mal

acca

Stra

it -

335,

87

- -

- -

-

354

S. T

apun

g Ki

ri -

- 5,

29

24,7

8 0,

22

4,71

29

,71

362

S. T

apun

g Ka

nan

- -

3,54

9,

12

0,09

0,

28

9,49

363

S. T

apun

g Ka

nan

- -

3,17

12

,51

0,03

0,

24

12,7

8

364

S. T

apun

g Ki

ri -

- 3,

54

9,71

0,

12

0,06

9,

89

365

S. T

apun

g Ki

ri -

- 0,

67

9,56

0,

20

0,06

9,

82

366

Siak

-

- 0,

75

8,62

0,

14

0,11

8,

87

367

Siak

-

- 3,

78

10,2

2 0,

10

0,15

10

,48

368

Siak

-

- 2,

56

13,2

2 0,

05

0,35

13

,62

Acknowledgements

I would like to thank Dr. Tim Rixen for all his support as well as his endurance with

which he has introduced me to scientific writing! He has contributed considerably to

the fun I had doing this PhD.

I am grateful to Prof. Dr. Wolfgang Balzer who kindly accepted the second

supervision.

I am very thankful to Prof. Dr. Venugopalan Ittekkot for his support and motivating

discussions during the time of my PhD thesis.

Many thanks to Dr. Daniela Unger who gave me valuable advice and support at all

times and who has kindly agreed to be member of my thesis committee.

I am very grateful to Matthias Birkicht, Doro Dasbach, Dieter Peterke and Ole

Morisse for the numerous analyses, valuable advices and support during the

laboratory work. Without them this work would not have been possible.

Thanks are given to Dr. Joko Samiaji, Dr. Christine Jose and all the colleagues and

students of the University Riau (Pekanbaru) for their support and help during my time

in Indonesia.

I am grateful to Csilla Kovacs for her dedicated help at the ZMT and in Indonesia. I

very much enjoyed spending so much time with her and captain Hany.

Sincere thanks to all colleagues at the ZMT for giving me scientific support and

helping me manage all the administrative and financial challenges. I kindly thank

Esther Borell for proofreading the papers and for being around these last few years. I

very much enjoyed the cooperation, help and friendship of so many Phd students

(and those who already made it) who joined me during my time at ZMT. Thank you

very much! In this context special thanks go to Anne Baumgart, Claudia Propp, Dr.

Inga Nordhaus, Dr. Kerstin Kober and Dr. Bettina Schmitt.

I kindly thank my parents for believing in me and always supporting my decisions.

Finally, I thank Timo Ebenthal who always supported and encouraged me all these

years.

Liste der veröffentlichten und eingereichten Artikel

Die vorliegende Arbeit besteht aus mehreren eigenen Artikeln die in referierten

Fachzeitschriften eingereicht und veröffentlicht wurden. Der Eigenanteil in Bezug auf

Idee- und Konzeptentwicklung, Datenerhebung und Auswertung sowie das

Verfassen der einzelnen Artikel ist im Folgenden beschrieben:

Artikel 1 Titel: Sources of dissolved inorganic nutrients in the peat-draining river Siak, Central

Sumatra, Indonesia

Autoren: Antje Baum, Tim Rixen, Gerd Liebezeit, Ralf Wöstmann, Christine Jose,

Joko Samiaji

Fachzeitschrift: Biogeochemistry, eingereicht am 3. Juni 2008

Idee und Konzept dieses Artikels wurden von Antje Baum entwickelt. Probennahme

der Flusswasser- und Bodenproben sowie deren Analyse wurde von Antje Baum

durchgeführt. Die Daten wurden von Antje Baum ausgewertet und mit den Co-

Autoren diskutiert. Der Artikel wurde von Antje Baum verfasst. Eine Durchsicht des

Artikels erfolgte durch die Co-Autoren, deren Anmerkungen und Verbesserungen bei

der Überarbeitung des Artikels berücksichtigt wurden.

Artikel 2 Titel: The Siak, a tropical black water river in central Sumatra on the verge of anoxia Autoren: Tim Rixen, Antje Baum, Thomas Pohlmann, Wolfgang Balzer, Joko

Samiaji, Christine Jose

Fachzeitschrift: Biogeochemistry, eingereicht am 10. Juni 2008

Idee und Konzept dieses Artikels wurde von Tim Rixen entwickelt. Der Eigenanteil an

diesem Artikel lag hauptsächlich in der Datenerhebung, Analyse und Auswertung

sowie der Durchführung des Abbauexperiments.

Artikel 3 Titel: Relevance of peat draining rivers in central Sumatra for riverine input of

dissolved organic carbon into the ocean Autoren: Antje Baum, Tim Rixen, Joko Samiaji

Fachzeitschrift: Estuarine, Coastal and Shelf Science 73 (2007) 563-570;

eingereicht am 8. August 2006; akzeptiert am 21. Februar 2007

Idee und Konzept dieses Artikels wurden von Antje Baum entwickelt. Die

Probennahme wurde größtenteils von Antje Baum und Tim Rixen und Analyse der

Proben von Antje Baum durchgeführt. Die Auswertung der Daten erfolgte durch Antje

Baum mit Unterstützung von Tim Rixen. Der Artikel wurde von Antje Baum verfasst.

Eine Durchsicht des Artikels erfolgte durch die Co-Autoren, deren Anmerkungen und

Verbesserungen bei der Überarbeitung des Artikels berücksichtigt wurden.

Artikel 4 Titel: DOC discharges from the Indonesian blackwater river Siak and its estuary into

the Malacca Strait and their role as DOC source for the Indian Ocean

Autoren: Antje Baum, Tim Rixen, Herbert Siegel, Thomas Pohlmann, Joko Samiaji,

Christine Jose

Fachzeitschrift: Marine Chemistry, eingereicht am 11. Juni 2008

Idee und Konzept dieses Artikels wurden von Antje Baum entwickelt. Entnahmen der

DOC-Proben, deren Analysen und Auswertung wurden von Antje Baum

durchgeführt. Die Daten wurden von Antje Baum ausgewertet, die die Ergebnisse

zusammen mit Beiträgen der Co-Autoren (Fernerkundung, Modellierung; Kapitel

„Distribution of riverine DOC in the coastal ocean“) in diesem Artikel dargestellt und

diskutiert hat. Eine Durchsicht des Artikels erfolgte durch alle beteiligten Autoren,

deren Anmerkungen und Verbesserungen bei der Überarbeitung des Artikels

berücksichtigt wurden.

Erklärung

Gemäß §6 der Promotionsordnung der Universität Bremen für die mathematischen,

natur- und ingenieurwissenschaftlichen Fachbereiche vom 14. März 2007 versichere

ich, dass:

- die Arbeit ohne unerlaubte fremde Hilfe angefertigt wurde

- keine anderen als die angegebenen Quellen und Hilfsmittel benutzt wurden

- die den benutzten Werken wörtlich oder inhaltlich entnommenen Stellen als solche

kenntlich gemacht wurden

Bremen, 2. September 2008

(Antje Baum)

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