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ISSA Workshop, February 10 - 12, 2005, Hotel Santon, Brno

Hydrobiologic al Institute of the A c adem y of Sciences CR Na Sádkách 7, 370 05 České Budějovice , Czech Republic www.hbu.cas.cz.

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ISSA Workshop, February 10 - 12, 2005, Hotel Santon, Brno

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  1. HydrobiologicalInstituteof the Academy of Sciences CR Na Sádkách 7, 370 05 České Budějovice, Czech Republic www.hbu.cas.cz Nutrients Load As a Risks Factor in Freshwater Sediments: Assessment, Effects and ReductionJ. Hejzlar, J. Borovec and J. KopáčekHydrobiological Institute AS CR and Faculty of Biological SciencesUSB,České Budějovice, Czech Republic ISSA Workshop, February 10 - 12, 2005, Hotel Santon, Brno

  2. Outline: Risks of increased nutrient loading for sediments Internal loading of P and its assessment Measures to decrease internal loading of P Designing a lake restoration program 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 (O2, NO3-, SO42-), 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 Ploading

  4. INPUT Net retention: Sedimentation > Release Net release: Sedimentation < Release OUTPUT RELEASE SEDIMENTATION 2. Internal loading of P and its assessment Internal loading = Release from sediment 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 capacityof mineralcomponent 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) a) b) c)input - hypominion experiments output accumulation balance INPUT OUTPUT 5 10 RELEASE SEDIMENTATION 10 5 - 5 >5 5

  6. “RELEASABLE“ P 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) ii. P-release potential evaluation(all releasable species under any conditions)a) changes in sediment P-concentration profile

  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/precipitationc) release mechanisms: mineralization, pH-pE dependent dissolution/desorption, resuspension, bioturbation

  8. Diagenetic transformations of P-forms in sediments water S,Re benthicboundarylayer S,Re S,Re D,Re S,Re exchangeable inorganic P So M,U refractory organic P labile organic P stable inorganic P dissolved inorganic P Prec Bu,Bi,Re Bu,Bi,Re Bu,Bi,Re Bu,Bi,Re D,Bi,Re exchangeable inorganic P So M,U refractory organic P labile organic P stable inorganic P dissolved inorganic P Prec active sediment Bu Bu D Bu Bu Bu inactive sediment modified from Schauser et al. 2004 Bi – bioturbation, Bu – burial, D – diffusion, M – mineralization, Prec – precipitation, U – uptake, Re – resuspention, S – sedimentation, So – sorption,

  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):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)

  10. 3. Measures to decrease internal loading of P Measure Controlling factor Effectiveness Duration Oxidation with Redox potential Low Short-termNO3- 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

  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 B. Selection: Select the most suitable measure by cost/efficiency criteria Assessment by experts Unsuitable measures Suitable measures

  13. 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

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

  15. 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 35% 38% 60% Inflow-outflow changes of P concentrations Dissolved reactive P Total P summer stratification - P deposition non-vegetation period – mineralization and release

  16. Inflow part - rapid turnover of settled sestonStratified lacustrine part – seasonal cycle of sedimentation-release Seasonal changes in sediment composition DM, % TOC, mg/g TON, mg/g TP, mg/g Fe, mg/g

  17. Pore water – seasonal changes of P concentration (peeper technique) Inflow part Dam part releaseno release January October June June October January April April Jo-A Jo-B January 3, 2002

  18. Phosphorus fractions (Psenner & Pucsko 1988) Indicators of P-release mechanismsno-release valueP 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 High potential of P release from seston ! Low potential of P release from sediment ! Sediment composition assessment

  19. High external P-load is the main cause of hypertrophy Rapid response to decrease in external P-load Single measures not durable Highly improbable lasting effect of internal P-loading after drop in external P-load Al-treatment suitable only in the dam part Basic information pro selection of internal measures in Jordán Reservoir Parameter Value Contemporary external load 2.1g m2yr-1 (Pin-lake = 104 mg m-3) Critical external load 0.6g m2yr-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 m2yr-1 Release potential (from a 30-cm layer) 0.8 g m2 Stratification dimictic Depth of resuspention 2 to 5 m Effective types of measures - continuous P-binding compound addition- hypolimnetic withdrawal (partly)

  20. Conclusions 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 ! Sediment with Polygonum amphibium a Limosella aqautica in mesotrophic Nýrsko Reservoir, Czech Republic

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