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![Page 1: Nutrients Load As a Risks Factor in Freshwater Sediments: Assessment, Effects and Reduction J. Hejzlar, J. Borovec and J. Kopáček Hydrobiological Institute.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649eb65503460f94bbed37/html5/thumbnails/1.jpg)
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
![Page 2: Nutrients Load As a Risks Factor in Freshwater Sediments: Assessment, Effects and Reduction J. Hejzlar, J. Borovec and J. Kopáček Hydrobiological Institute.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649eb65503460f94bbed37/html5/thumbnails/2.jpg)
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
![Page 3: Nutrients Load As a Risks Factor in Freshwater Sediments: Assessment, Effects and Reduction J. Hejzlar, J. Borovec and J. Kopáček Hydrobiological Institute.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649eb65503460f94bbed37/html5/thumbnails/3.jpg)
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
![Page 4: Nutrients Load As a Risks Factor in Freshwater Sediments: Assessment, Effects and Reduction J. Hejzlar, J. Borovec and J. Kopáček Hydrobiological Institute.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649eb65503460f94bbed37/html5/thumbnails/4.jpg)
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
![Page 5: Nutrients Load As a Risks Factor in Freshwater Sediments: Assessment, Effects and Reduction J. Hejzlar, J. Borovec and J. Kopáček Hydrobiological Institute.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649eb65503460f94bbed37/html5/thumbnails/5.jpg)
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
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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
![Page 7: Nutrients Load As a Risks Factor in Freshwater Sediments: Assessment, Effects and Reduction J. Hejzlar, J. Borovec and J. Kopáček Hydrobiological Institute.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649eb65503460f94bbed37/html5/thumbnails/7.jpg)
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
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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
![Page 9: Nutrients Load As a Risks Factor in Freshwater Sediments: Assessment, Effects and Reduction J. Hejzlar, J. Borovec and J. Kopáček Hydrobiological Institute.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649eb65503460f94bbed37/html5/thumbnails/9.jpg)
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)
![Page 10: Nutrients Load As a Risks Factor in Freshwater Sediments: Assessment, Effects and Reduction J. Hejzlar, J. Borovec and J. Kopáček Hydrobiological Institute.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649eb65503460f94bbed37/html5/thumbnails/10.jpg)
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
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4. Designing a lake restoration program by control of nutrient release from sediments
DECISION SUPPORT TOOL (Schauser et al. 2003)
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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
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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
![Page 14: Nutrients Load As a Risks Factor in Freshwater Sediments: Assessment, Effects and Reduction J. Hejzlar, J. Borovec and J. Kopáček Hydrobiological Institute.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649eb65503460f94bbed37/html5/thumbnails/14.jpg)
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
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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%
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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
![Page 17: Nutrients Load As a Risks Factor in Freshwater Sediments: Assessment, Effects and Reduction J. Hejzlar, J. Borovec and J. Kopáček Hydrobiological Institute.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649eb65503460f94bbed37/html5/thumbnails/17.jpg)
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
![Page 18: Nutrients Load As a Risks Factor in Freshwater Sediments: Assessment, Effects and Reduction J. Hejzlar, J. Borovec and J. Kopáček Hydrobiological Institute.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649eb65503460f94bbed37/html5/thumbnails/18.jpg)
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 !
![Page 19: Nutrients Load As a Risks Factor in Freshwater Sediments: Assessment, Effects and Reduction J. Hejzlar, J. Borovec and J. Kopáček Hydrobiological Institute.](https://reader035.fdocuments.us/reader035/viewer/2022062518/56649eb65503460f94bbed37/html5/thumbnails/19.jpg)
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)
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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 !