Nutrients Load As a Risks Factor in Freshwater Sediments: Assessment, Effects and Reduction J....
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Transcript of Nutrients Load As a Risks Factor in Freshwater Sediments: Assessment, Effects and Reduction J....
Nutrients Load As a Risks Factor
in Freshwater Sediments: Assessment, Effects and Reduction
J. Hejzlar, J. Borovec and J. Kopáček
Hydrobiological Institute AS CR and Faculty of Biological Sciences USB,
České Budějovice, Czech RepublicISSA Workshop, February 10 - 12, 2005, Hotel Santon, Brno
Hydrobiological Institute of the Academy of Sciences CR Na Sádkách 7, 370 05 České Budějovice, Czech Republic www.hbu.cas.cz
Outline:
1. Risks of increased nutrient loading for sediments
2. Internal loading of P and its assessment
3. Measures to decrease internal loading of P
4. Designing a lake restoration program
5. Example – Jordán Reservoir
1. Risks of increased nutrient loading
• increase in sedimentation rate – danger of siltation
• change of physical characteristics – water and organic content,
porosity
• change of chemistry
– increased use of electron acceptors (O2, NO3-, SO4
2-), decrease in
pE
– change of pH (CO2 and alkalinity production, H+ consumption)
– accumulation of reduced species (Mn, Fe, Co, Hg, S2-...)
• deterioration of biological quality
– toxicity (H2S, NH3, MeHg)
– loss of habitat
• water-sediment interactions
– release of reduced species in water (Mn, Fe, DOC, NH3, CH4, H2S...)
– release of PO4-P; internal P loading
2. Internal loading of P and its assessment
Internal loading = Release from sedimentINPUT OUTPUT
RELEASESEDIMENTATION
Net retention: Sedimentation > Release
Net release: Sedimentation < Release
Internal loading – one part of cycling between sediment and
water
– high in shallow, polymictic water bodies
– unimportant when HRT is short (<1 yr)
– depends on a ration of P-loading : P-binding
capacity
of mineral component of sediment
– influenced by physics, chemistry, and biology of
sediments
Assessment of internal P loading:
i. Apparent release rate (real in-lake conditions)
a) “input – output – in-lake change” balance (net release only)
b) accumulation of P in hypolimnion (release+mineralization in
water)
c) experimental incubations / sediment pore-water profiling
(release)INPUT OUTPUT
RELEASESEDIMENTATION
a) b) c)input - hypominion experiments output accumulation balance
10
10 5
5
- 5 >5 5
ii. P-release potential evaluation (all releasable species under any conditions)
a) changes in sediment P-concentration profile
soft-water reservoir
2%
27%
3%6%
62%
H2O
BD
NaOH-25°C
HCl
NaOH-85°C
acidified lake
5%2%3%
1%
89%
hard-water lake
11%
67%
15% 3% 4%
b) chemical extraction methods
Fractions (e.g., Psenner & Pucsko 1988)
1. loosely bound (H2O), 2. redox labile (BD), 3. metal hydroxyoxides bound (NaOH20°C),
4. apatite bound (HCl), 5. refractory-organics bound (NaOH85°C)
0 1 2 3
1
5
9
13
17
21
25
29
33
37
H, c
m
P, mg/g
“R
ELEA
SA
BLE“
P
iii. P-retention/release mechanism (for real in-lake conditions)
a) major binding compounds:
Fe (lowland, soft waters), Al (acidified catchments), Ca (hard waters)
b) retention processes:
sedimentation, mineralization + adsorption/precipitation
c) release mechanisms:
mineralization, pH-pE dependent dissolution/desorption,
resuspension, bioturbation
water
benthicboundarylayer
active sediment
inactive sediment
modified from Schauser et al. 2004
Diagenetic transformations of P-forms in sediments
refractory organic P
refractory organic P
labile organic P
labile organic P
dissolved inorganic P
dissolved inorganic P
exchangeable inorganic P
stable inorganic P
exchangeable inorganic P
stable inorganic P
Bu Bu D Bu Bu
Prec
So
So
S,Re
S,ReS,Re S,Re D,Re
M,U
M,U
Bu,Bi,Re
D,Bi,Re
Bu,Bi,Re Bu,Bi
,Re
Prec
Bu
Bi – bioturbation, Bu – burial, D – diffusion, M – mineralization, Prec – precipitation, U – uptake, Re – resuspention, S – sedimentation, So – sorption,
Bu,Bi,Re
d) Indicators of P-release mechanisms:
No release if:
P in Settling-seston NVSS : P in Sediment NVSS < 1
Fe:P in sediment > 15 (Jensen et al. 1992)
Fe(II):Pdiss in pore water > 1 (Phillips et al. 1994)
Al(OH)3:Fe(OH)x in sediment > 3
or
Al(OH)3:Fe(OH)x in sediment < 3, but
Al(OH)3:PH2O+BD in sediment > 25 (Kopáček et al.
submitted)
Measure Controlling factor Effectiveness Duration
Oxidation with Redox potential Low Short-term
NO3- or O2
Precipitation with Al P-binding compound High Short to long-term
Precipitation with Fe P-binding compound Low to high Short-term
Co-precipitation P-binding compound Low to high Short to long-termwith calcite
Capping P-binding compound Depends on Short to long-term and porosity P-binding
Dredging P content Low to high Short-term
Hypolimnetic P-concentration in Low Long-termwithdrawal the hypolimnion
3. Measures to decrease internal loading of P
4. Designing a lake restoration program by control of nutrient release from sediments
DECISION SUPPORT TOOL (Schauser et al. 2003)
Flow diagram of the decision support
PREREQUISITES: 1. Is a control by P limitation useful for the lake and targets?
2. Is the target trophic state realistic? 3. Is a further reduction of the external load impossible?
All yes: decision support is suitable
DECISION SUPPORTA. Preselection: Exclude unsuitable measures by checking each measure in regard to suitability classes • current and critical external load • time characteristics of the lake – HRT, adaptation time, duration of effect • morphological structure of the lake – depth, stratificationFixed assessment by means of importance and
suitability
Suitable measures
Unsuitable measures
Assessment by experts
B. Selection: Select the most suitable measure by cost/efficiency criteria
5. Example – Jordán Reservoir(hyper-eutrophic conditions due to long-
lasting sewage discharges and diffuse pollution)
Lake parameter Value*
Area 0.43 km2
Volume 2.2 mil. m3
Maximum/Mean depth 11 m/5.1 m
Water retention time 0.25 yr
External P load 2.1 g m-2 yr-1
Inflow P 102 mg m-3
Outflow P 94 mg m-3
In-lake P 104 mg m-3
Chlorophyll a 20 mg m-3
Outlets surface
* average 2000, 2001, 2003
Tábor, South Bohemia, CR
cyanobacterial water bloom in summer 2000
cyanobacterial water bloom in summer 2000
organic sediments at sewage outlet
Longitudinal profile of water chemistry
September 4, 2000
Tem perature, °C
414
416
418
420
422
DO, m g/l
414
416
418
420
422
Alt
itu
de,
m a
.s.l.
DRP, µg/l
Total P, µg/l
2.0 2.5 3.0 3.5 4.0 4.5
River km
NH4-N, mg/l
2.0 2.5 3.0 3.5 4.0 4.5
River km
SO4, mg/l
414
416
418
420
422
0.00
0.05
0.10
0.15
0.20
I.00
IV.0
0V
II.0
X.0
0I.0
1IV
.01
VII.
0X
.01
I.02
IV.0
2IV
.03
VII.
0X
.03
I.04
TP, m
g/l
inflow
outflow
0
0.04
0.08
0.12
0.16
I.00
IV.0
0V
II.0
X.0
0I.0
1IV
.01
VII.
0X
.01
I.02
IV.0
2IV
.03
VII.
0X
.03
I.04
DR
P, m
g/l
inflow
outflow
Inflow-outflow changes of P concentrations
Total P Dissolved reactive P summer
stratification - P deposition
non-vegetation period – mineralization and release
-300
-150
0
150
300
450
600
2000 2001 2003
Tota
l P ,
kg
Input, kg Ret.IV-IX, kg
Ret.X-III, kg Ret., kg1570
Input-output balance: Retention = Pin – Pout - Paccum
Ret.X-III ≈ Release
Year Release [kg] [% Ret.IV-IX]
2000 73 38
2001 238 60
2003 33 35
38%
60%
35%
Seasonal changes in sediment composition
DM, % TOC, mg/g TON, mg/g TP, mg/g Fe, mg/g
Inflow part - rapid turnover of settled sestonStratified lacustrine part – seasonal cycle of sedimentation-release
Pore water – seasonal changes of P concentration (peeper technique)
0 1 2 3 4-10
-5
0
5
DRP (mg l-1)
dept
h (c
m)
0 1 2 3 4 5 6
9.7.29.10.17.1.
10.4.
DRP (mg l-1)
Inflow part
Jo-B
Dam part
April
JuneOctoberJanuary
January
October
April
June
Jo-A
January 3, 2002
releaseno release
Sediment composition assessment
dam3%
18%
36%
39%
4%
H2O
BD
NaOH-25°C
HCl
NaOH-85°C
inflow
2%
24%
27%
10%
37%
Phosphorus fractions (Psenner & Pucsko 1988)
Indicators of P-release mechanisms no-
release value
P in Seston NVSS (9.3 mg g-1) : P in Sediment NVSS (2.8 mg g-1) = 3.5 < 1
Fe:P in sediment = 13.5 >
15
Fe(II):Pdiss in pore water = 0.7 (dam part), 7 (inflow part) > 1
Al(OH)3:Fe(OH)x in sediment = 4 (dam part), 0.5 (inflow part) >
3
or
Al(OH)3:Fe(OH)x in sediment < 3, but
Al(OH)3:PH2O+BD in sediment = 90 (dam part), 26 (inflow part) >
25
Low potential of P release from sediment
!
High potential of P release from seston !
Basic information pro selection of internal measures in Jordán Reservoir
Parameter Value
Contemporary external load 2.1 g m2
yr-1
(Pin-lake = 104 mg m-3)
Critical external load 0.6 g m2 yr-1
(Ptarget = 20 mg m-3)
Adaptation time 0.75 yr
Duration of effect for a single measure 0.9 yr
Release rate 0.3 g m2 yr-1
Release potential (from a 30-cm layer) 0.8 g m2
Stratification dimictic
Depth of resuspention 2 to 5 m
High external P-load is the main cause of hypertrophy
Rapid response to decrease in external P-load
Single measures not durable
Al-treatment suitable only in the dam part
Highly improbable lasting effect of internal P-loading after drop in external P-load
Effective types of measures - continuous P-binding compound addition
- hypolimnetic withdrawal (partly)
Conclusions
Sediment with Polygonum amphibium a Limosella aqautica in mesotrophic Nýrsko Reservoir, Czech Republic
1. Excessive nutrient loading in lakes affects composition of sediments and impacts biota and water quality
2. Sediments are a dynamic component of aquatic ecosystem: - coupled with water chemistry - with time response related to water residence time
3. Assessment of sediments as a source of internal P-loading can be reliably done by chemical analysis and mass-balance studies
4. Measures to treat internal P-loading can be optimised based on functional suitability / cost criteria Thank you for your
attention !