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Dr. Martin T. Auer MTU Department of Civil & Environmental Engineering CE5504 Surface Water Quality Modeling Lab 5. Sediment-Water Exchange The Recovery of Shagawa Lake, Minnesota: Sediment Mediation
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Contaminant Association with Particulate Matter Biological Uptake Abiotic Adsorption
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Onondaga Lake, NY depositional basin Depositional Basins
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Diagenesis The sum total of processes that bring about changes in a sediment subsequent to deposition in water. Berner 1980
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diagenesis – redox reactions depositionflux Sediment Recycle (Internal Loads)
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oxic conditions; sparingly soluble anoxic conditions; highly soluble Phosphorus Biogeochemistry
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Seasonality in P Release
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Hypolimnetic P Accumulation
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1. Sediment Removal (Dredging) 2. Hypolimnetic Withdrawal 3. Chemical Inactivation 4. Artificial Circulation 5. Hypolimnetic Aeration 6. Sediment Oxidation Support Raft Gas Vent Support Cables Contact Chamber Air Line & Diffuser Ballast Engineered Remediation
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The Slow Eigenvalue old SS new SS concentration time for the sediment for the water column Monitored Natural Recovery
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Natural Recovery: diffusion and burial Burial Pore Water Diffusion
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Weak Sorber t d +3 t d +5 t d +10 t d +20 t d +30 t d +50 Weak sorber log K d ~ 2.5
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Strong Sorber t d +3 t d +5 t d +10 t d +20 t d +30 t d +50 Strong sorber log K d ~ 6
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Diagenesis and Recovery – Part I
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Diagenesis and Recovery – Part II
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Diagenesis and Recovery – Part III
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Modeling Sediment – Water Interactions 8 load outflow deposition release burial
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The Limiting Nutrient Concept The Supplies The Product
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The Limiting Nutrient Controversy
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Shagawa Lake
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eutrophic system tertiary treatment installed in 1973 load reduction of 80%
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Shagawa Lake The (un)response
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Shagawa Lake A mathematical model predicted that the lake would reach equilibirium P levels of 12 ppb in ~1.5 years. The fact that it didn’t was attributed to sediment P feedback, primarily during summer. Modification of the model to accommodate sediment P release matches post-treatment P levels well and indicates that P release has not been diminished since treatment went on line. Further recovery will depend on the time course of reductions in sediment feedback.
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