1. 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 Republic ISSA 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

2. 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

3. 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 (O 2, NO 3 -, SO 4 2- ), decrease in pE – change of pH (CO 2 and alkalinity production, H + consumption) – accumulation of reduced species (Mn, Fe, Co, Hg, S 2-...) deterioration of biological quality – toxicity (H 2 S, NH 3, MeHg) – loss of habitat water-sediment interactions – release of reduced species in water (Mn, Fe, DOC, NH 3, CH 4, H 2 S...) – release of PO 4 -P; internal P loading

4. 2. Internal loading of P and its assessment Internal loading = Release from sediment INPUT OUTPUT RELEASE SEDIMENTATION 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

5. 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) INPUTOUTPUT RELEASE SEDIMENTATION a) b) c) input - hypominion experiments output accumulation balance 10 5 5 - 5>55

6. ii. P-release potential evaluation (all releasable species under any conditions) a) changes in sediment P-concentration profile b) chemical extraction methods Fractions (e.g., Psenner & Pucsko 1988) 1. loosely bound (H 2 O), 2. redox labile (BD), 3. metal hydroxyoxides bound (NaOH 20°C ), 4. apatite bound (HCl), 5. refractory-organics bound (NaOH 85°C ) “RELEASABLE“ P

7. 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

8. water benthic boundary layer active sediment inactive sediment modified from Schauser et al. 2004 Diagenetic transformations of P-forms in sediments refractory organic P labile organic P dissolved inorganic P exchangeable inorganic P stable inorganic P exchangeable inorganic P stable inorganic P Bu D Prec So S,Re D,Re M,U Bu,Bi,Re D,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

9. 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):P diss 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 25 (Kopáček et al. submitted)

10. Measure Controlling factor Effectiveness Duration Oxidation with Redox potential Low Short-term NO 3 - or O 2 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-term with 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-term withdrawal the hypolimnion 3. Measures to decrease internal loading of P

11. 4. Designing a lake restoration program by control of nutrient release from sediments DECISION SUPPORT TOOL (Schauser et al. 2003)

12. 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 SUPPORT A. 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, stratification Fixed 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

13. 5. Example – Jordán Reservoir (hyper-eutrophic conditions due to long-lasting sewage discharges and diffuse pollution) Lake parameterValue* Area0.43 km 2 Volume2.2 mil. m 3 Maximum/Mean depth11 m/5.1 m Water retention time 0.25 yr External P load2.1 g m -2 yr -1 Inflow P102 mg m -3 Outflow P 94 mg m -3 In-lake P104 mg m -3 Chlorophyll a20 mg m -3 Outletssurface * average 2000, 2001, 2003 Tábor, South Bohemia, CR

14. cyanobacterial water bloom in summer 2000 organic sediments at sewage outlet Longitudinal profile of water chemistry September 4, 2000

15. Inflow-outflow changes of P concentrations Total P Dissolved reactive P summer stratification - P deposition non-vegetation period – mineralization and release Input-output balance: Retention = P in – P out - P accum Ret.X-III ≈ Release Year Release [kg] [% Ret.IV-IX] 2000 73 38 2001 238 60 2003 33 35 38% 60% 35%

16. Seasonal changes in sediment composition DM, %TOC, mg/gTON, mg/gTP, mg/gFe, mg/g Inflow part - rapid turnover of settled seston Stratified lacustrine part – seasonal cycle of sedimentation-release

17. Pore water – seasonal changes of P concentration (peeper technique) Inflow part Jo-B Dam part April June October January October April June Jo-A January 3, 2002 release no release

18. Sediment composition assessment 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):P diss 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 25 Low potential of P release from sediment ! High potential of P release from seston !

19. Basic information pro selection of internal measures in Jordán Reservoir Parameter Value Contemporary external load 2.1 g m 2 yr -1 (Pin-lake = 104 mg m -3 ) Critical external load 0.6 g m 2 yr -1 (P target = 20 mg m -3 ) Adaptation time 0.75 yr Duration of effect for a single measure 0.9 yr Release rate 0.3 g m 2 yr -1 Release potential (from a 30-cm layer) 0.8 g m 2 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 durableAl-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)

20. 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 !