Eric Struyf Kris Bal Sofie Van Belleghem Patrick Meire

Top-bottom investigation of water and Top-bottom investigation of water and nutrient fluxes to the coastal zone through nutrient fluxes to the coastal zone through

a lowland river basina lowland river basin

Eric Struyf

Kris Bal

Sofie Van Belleghem

Patrick Meire

Introduction

The accurate quantification of fluxes of water and fluxes of dissolved constituents throughout whole river basins is of major importance.

This study can act as the working tool for river managers and modellers to anticipate future changes in hydrology due to climate change and development of vegetation throughout the Schelde basin (France, Belgium, The Netherlands)

Overview

Focus on two research projects within the total framework of integrated river basin management

1. The effect of vegetation on drainage in upper river basin sub catchments

2. The possible effect of changing external forcing conditions (increasing discharge) on the eventual transport of water and nutrients towards the coastal area through estuarine ecosystems

Dendermonde

Vlissingen

Gent

Temse Antwerp

Belgian-Dutch borderNorth Sea

Sche

lde

Schelde

Schelde

Dender

Rupel

Durme

Channel Gent-Terneuzen

North sea

The Schelde estuary

-Entire salt gradient-Highly eutrofied-Highly industrialized

Nete sub-catchment

Struyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press

Part 1 :Part 1 :

The effects of mowing on The effects of mowing on the discharge capacity the discharge capacity

of lowland riversof lowland rivers

Increased nutrient fluxes towards the river stimulate plant growth :

- discharge capacity will decrease

- possibility that adjacent valuable land will flood

Pro’s and cons of watervegetation

Pro :

- Vegetation acts as a sieve for suspended solids and nutriënts

- Vegetation acts as refugia areas for organisms during

extreme discharge conditions.

- Vegetation has a positive effect on the diversity of

organisms within and outside a river

Contra :

- increases the resistance

- often seen as a nuisance in waterways (perception)

This study

- Partial removement of macrophytes in three different mowing patterns for three different macrophytes

- Patterns with the most ecological potential

This as a compromise between the drainage and life support function of waterways

Pattern 1 Pattern 3

Pattern 2 : two sides of macrophytes

In-situ determination of biomass

Biomass Grote Caliebeek

0

0,5

1

1,5

2

Jan March April June Aug Okt Nov

Month

fres

hw

eig

ht

(kg

/m2)

Biomass Wamp

0

0,1

0,2

0,3

0,4

0,5

0,6

Jan March April May June Aug Okt Nov

month

fres

hw

eig

ht

(kg

/m2)

Biomass Slootbeek

0

0,1

0,2

0,3

0,4

0,5

0,6

Jan March April May June Aug Okt Nov

Month

Fre

shw

eig

ht

(kg

/m2)

Biomass Aa

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

Jan March May June July Aug Sept Okt Nov

Month

fre

sh

we

igh

t (k

g/m

2)

Streamvelocity within the patterns (ex-situ)vegetationVelocity is higher for pattern 2 (all species)

Ranunculus aquatilis

00,020,040,060,080,1

0,120,140,16

0 0,05 0,1 0,15

discharge (m3 s-1)

aver

age

stre

am v

elo

city

(m

s-1

) pattern 1

pattern 2

pattern 3

Callitriche species

0

0,02

0,04

0,06

0,08

0,1

0,12

0,14

0 0,05 0,1 0,15

discharge (m3 s-1)

aver

age

stre

am v

elo

city

(m

s-1

) pattern 1

pattern 2

pattern 3

Potamogeton natans

00,020,040,060,080,1

0,120,140,16

0 0,05 0,1 0,15

discharge (m3 s-1)

aver

age

stre

am v

elo

city

(m

s-1

)

pattern 1

pattern 2

Open water

Velocity in pattern 2 is slightly higher then in the other

patternsPotamogeton natans

0

0,05

0,1

0,15

0,2

0,25

0 0,05 0,1 0,15

discharge (m3/s)

aver

age

stre

am v

elo

city

(m

/s) pattern 1

pattern 2


0

0,05

0,1

0,15

0,2

0,25

0,3

0 0,05 0,1 0,15

discharge (m3/s)

aver

age

stre

am v

elo

city

(m

/s) éénkant

tweekant

dambord

Callitriche species

00,050,1

0,150,2

0,250,3

0,350,4

0 0,05 0,1 0,15

discharge (m3/s)

aver

age

stre

am v

elo

city

(m

/s)

pattern 1

pattern 2

pattern 3

Determination of the resistance ex-situ

Pattern 2 had the highest Km values especially in the higher discharge

range Km = V*(R2/3*S1/2)-1

0

0,02

0,04

0,06

0,08

0,1

0,12

0,14

0,16

0,18

0 10 20 30 40 50 60

Km (m1/3 s-1)

dis

char

ge

(m3/s

ec)

pattern 2

pattern 1

pattern 3

Pattern influence

Km values of pattern 1

0

0,02

0,04

0,06

0,08

0,1

0,12

0,14

0 20 40 60 80 100

Km (m1/3 s-1)

Dis

char

ge

(m3/s

ec)


Potamogeton natans

Callitriche species

Species influence

- species with their biomass at the watersurface have higher Km values

Km values of pattern 2

0

0,05

0,1

0,15

0,2

0 20 40 60 80

Km (m1/3 s-1)

dis

char

ge

(m3/s

ec)


Potamogeton natans

Callitriche species

Conclusion

- Pattern two has the lowest resistance despite of higher biomasses

- Plant architecture influences the resistance :

* species with high leaf areas (Callitriche sp.) and branched leaves (Ranunculus aquatilis) have high resistances

* concentration of biomass at the surface will impede the water flow less

- The patterns have a better relative drainage at higher discharges

Part 2: Part 2: the effects of hydrological the effects of hydrological changes on nutrient changes on nutrient fluxes throughout fluxes throughout estuarine waters to the estuarine waters to the coastal zonecoastal zone


Changes in hydrological conditions throughout the Changes in hydrological conditions throughout the river shed eventually influence discharge conditions in river shed eventually influence discharge conditions in estuarine waters and can result in:estuarine waters and can result in:

- major changes in nutrient fluxes towards brackish major changes in nutrient fluxes towards brackish and salt estuarine and coastal watersand salt estuarine and coastal waters

- major changes in nutrient concentrations in the major changes in nutrient concentrations in the freshwater part of estuarine watersfreshwater part of estuarine waters


Why is nutrient flux towards and through estuarine waters so important?

-Estuarine and coastal waters are the main fishery grounds on EarthEstuarine and coastal waters are the main fishery grounds on Earth

-Diatom communities are fundamental in estuarine food webs and play Diatom communities are fundamental in estuarine food webs and play an essential role in productivityan essential role in productivity

-The optimal balance between diatom communities and less preferred The optimal balance between diatom communities and less preferred fytoplankton communities (e.g green algae) is dependent on nutrient fytoplankton communities (e.g green algae) is dependent on nutrient ratios within coastal watersratios within coastal waters

- Increase in N and P fluxes to coastal waters can induce eutrophication Increase in N and P fluxes to coastal waters can induce eutrophication (explosive growth of algae e.g. (explosive growth of algae e.g. PhaeocystisPhaeocystis) and subsequent negative ) and subsequent negative effects as oxygen depletion, fish kills, foam production...effects as oxygen depletion, fish kills, foam production...


Picture taken from: http://staff.science.uva.nl/~dcslob/lesbrieven/TomTahey/bovenbouwtekst3.htm

Eutrophication


This case study

-1996-2000: a period characterised by steadily increasing 1996-2000: a period characterised by steadily increasing discharges in the Schelde estuary discharges in the Schelde estuary

-The period 1996-2000 was taken as a reference period for The period 1996-2000 was taken as a reference period for possible major future changes in hydrological conditionspossible major future changes in hydrological conditions

- Vegetation in upper catchments- Vegetation in upper catchments- Global change- Global change- Urbanisation- Urbanisation


0

10

20

30

40

50

60

70

80

1996 1997 1998 1999 2000

Year

Dis

cha

rge

(m3 .s

-1)

Discharge from freshwater part towards brackish and coastal waters increased 2 to 3 fold in between 1996-2000.

73 m3.s-1

28 m3.s-1

Yearly average discharge in the freshwater zone of the estuary


0

20

40

60

80

100

120

140

160

jan-96 jan-97 jan-98 jan-99 jan-00

Date

Dis

char

ge

(m3.s

-1)

Increasing discharge apparent in both winter and summer: absolute discharge increase was higher in winter


0

5000

10000

15000

20000

1996 1997 1998 1999 2000

Dis

ch

arg

ed

lo

ad

(to

ns) ammonia

nitrate

nitrite

Increase in nitrate loadings

0

10

20

30

40

50

60

70

80

1996 1997 1998 1999 2000

Year

Dis

cha

rge

(m

3 .s-1

)

Nitrate input from the freshwater to the brackish increased Nitrate input from the freshwater to the brackish increased concurrently with discharge, ammonia loadings were stableconcurrently with discharge, ammonia loadings were stable

Discharges in the freshwater estuary

Dissolved nitrogen output doubled Dissolved nitrogen output doubled between 1996-2000between 1996-2000

8000 tons

16500 tons


Higher run-off

0

50000

100000

150000

200000

250000

300000

350000

1996 1997 1998 1999

Year

Dis

char

ged

SS

(to

ns)

0

5000

10000

15000

20000

25000

1996 1997 1998 1999 2000

Year

N (

ton

s)

Nitrate discharge Antwerp Agriculture loss


Non-point pollution (mainly agriculture) towards the estuary increased

Discharged suspended solids towards the estuary: indicator for surface run-off

Similar patterns in nitrate discharge and loss from agricultural soil, nitrate mainly originates from agriculture, ammonia relates

to point-pollution.

Estimates show a big increase

90000 tons

340000 tons

Source: AWZ Source: VMM

0

1000

2000

3000

4000

1996 1997 1998 1999 2000

Dis

char

ged

lo

ad (

ton

s)totP

DRP

0

5000

10000

15000

20000

1996 1997 1998 1999 2000

Dis

char

ged

lo

ad (

ton

s) DSi

P and Si discharge

Dissolved silica export tripled

Phosphorus export was less influenced

Hydrology changes can have major impact on

nutrient ratiosStruyf E., S. Van Damme, P. Meire 2004: Estuarine, Coastal and Shelf Science: in press

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

0 0,5 1 1,5 2 2,5

log (discharge+1)

log

(n

itra

te+

1)

winter-autumn

spring-summer

0

0,2

0,4

0,6

0,8

1

1,2

0 0,5 1 1,5 2 2,5

log (discharge+1)

log

(am

mo

nia

+1)

winter-autumn

summer-spring

Nitrogen in the freshwater zone


In winter, nitrate concentrations In winter, nitrate concentrations increase with discharge, in increase with discharge, in summer they decrease.summer they decrease.Relations were opposite for Relations were opposite for ammonia.ammonia.

winter

summer

summer

winter

The natural, seasonal cycle The natural, seasonal cycle appears to be flattened out by appears to be flattened out by increasing dischargeincreasing discharge

The amount of nitrate in the Schelde however is alsoinfluenced by the presence or absence of macrophytes in the upper sub-catchments (Nete)

Aa November 2003

0,0

1,0

2,0

3,0

4,0

5,0

6,0

7,0

8,0

9,0

10:00 22:00 10:00

time

tot

N (

mg

/l)

stuw 3

halfway

stuw 4

When macrophytes are present (Summer) total N concentrations are lowered. When the plants decay (Winter) N is released which causes an increased N flux towards the upper sub-catchment and eventually the schelde

Aa Augustus 2003

0,0

1,0

2,0

3,0

4,0

5,0

6,0

7,0

8,0

9,0

0:00 12:00 0:00

time

tot

N (

mg

/l)

stuw 3

halfway

stuw 4

Data S. Van Belleghem

0

0,2

0,4

0,6

0,8

1

1,2

0 0,5 1 1,5 2 2,5

log (discharge+1)

log

(D

Si+

1)

winter-autumn

spring-summer

summer

winter

Silica in the freshwater zone

Diatoms: summer - spring: uptake of DSi winter - autumn: no uptake

With increasing discharge, summer concentrations approach winter concentrations

Diatom communities appear not adapted to high discharges


Impact on management

Higher discharges appear to:

- dilute pollutants and nutrients

- increase nutrient loadings towards coastal zone

Dilution effect masks the problem of increasing loadings from non-point pollution.

Dilution could affect political and public perception about the effectivity of pollution reducing measures


0

50

100

150

200

250

300

350

400

Ex

pe

ns

es

(1

06 €)

1989 1991 1993 1995 1997 1999

Year

Flemish government has drastically increased investments in point-pollution reduction in the last decade to REDUCE nutrient loadings.

Due to hydrological changes, the nutrient loadings have increased over the same period.

Source: VMM


General conclusion

* Global change will increase discharge. Consequently nutrient run-off towards coastal zones will increase.

* Vegetation however increases the residence time of water due to higher resistances. Self purifying capacity of the river is restored through the stimulation of ecosystem processes.

* Vegetation management is a tool which can buffer the fluctuations in discharge in the river basin.

AcknowledgementsWe like to thank L. Clement for analyzing our water samples.

We especially like to thank Flanders Hydraulics and AWZ for their cooperation

Eric Struyf Kris Bal Sofie Van Belleghem Patrick Meire

Documents

Transcript of Eric Struyf Kris Bal Sofie Van Belleghem Patrick Meire