Mercury Processes
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The document describes the mercury cycle in watersheds and water bodies. It discusses the various natural and anthropogenic processes involving mercury emissions, transport, transformations between elemental, ionic, and methylated forms, and bioaccumulation through the aquatic food web. Key processes include atmospheric deposition, watershed runoff, methylation, demethylation, volatilization, oxidation, reduction, and biomagnification in fish.
Mercury Processes
- 1. Watershed Mercury Processes Anthropogenic Emissions Wet Deposition Dry Deposition Evasion Natural Emissions Percolation Shallow Ground Water Settling Resuspension Diffusion Runoff and Erosion Rivers and Streams Weathering Evasion Litterfall and Throughfall
- 3. Mercury in the Food Web Images from: www.glerl.noaa.gov/pubs/photogallery/gallery.html, www.dnr.state.wi.us Predator Fish: Yellow Perch Benthos MeHg Prey Fish: Yellow Perch Zooplankton Phytoplankton
- 4. Overview of WASP Mercury Module Volatile Exchange of Hg(0) Watershed and Atmospheric Loads of Hg(II) and MeHg State Variables Hg(0) Silt Hg(II) Sand MeHg Methylation Demethylation Oxidation Reduction Burial Point Source Loads of Hg(II) DOC
- 5. Mercury Processes in WASP Partitioning Transport Volatilization of Hg0(aq) to Hg0(air) Transformation Oxidation: Hg0 HgII Reduction: HgII Hg0 Methylation: HgII MeHg Demethylation: MeHg HgII Photoreduction: MeHg Hg0
- 6. Mercury Partitioning Processes Parameters : Enter Dissolved Organic Carbon Concentration Example Ranges: Oligotrophic Lake: <1 – 3 mg/L Mesotrophic Lake: <1 – 5 mg/L Eutrophic Lake: 5 – 30 mg/L Dystrophic Lake: 3 – 30 mg/L from Wetzel, 2001. 5-6 1.0e2 – 1.0e4 1.0e5 - 1.0e6 MeHg log K DOC K sand K fines Partition Coefficients 0 4 – 5 0 1.0e2 – 1.0e4 0 1.0e5 - 1.0e6 Hg0 HgII
- 7. Hg0 Volatilization Hg(0) diss to gaseous Hg(0) Constants: Set volatilization option (1 to 5), Henry’s Law constant (e.g., 7.1e-3 atm/M) Atmospheric concentration (e.g., 1.6e-9 g/m 3 )
- 8. Hg0 Oxidation Oxidation: Hg(0) to Hg(II) Hg0 Constants: Set phase switches (1 for dissolved) Yield coefficient (1.0) Parameters: Rate constants for water column segments (e.g., 1e-2 to 1e-3 day -1 )
- 9. HgII Transformation Processes Reduction: HgII to Hg(0) HgII Constants: Set photolysis option (2), Quantum yield coefficients (1 for diss, sorb), Yield coefficient (1.0), Surface rate constant (e.g., 1e-3 to 1e-1) Parameters: Light attenuation coefficients for water column segments (e.g., 0.5-2 m -1 )
- 10. HgII Transformation Processes Methylation: HgII to MeHg Constants: Set phase switches (1 for diss, sorb), Temperature correction factors (2.0 per 10 C change), Yield coefficient (1.07) Parameters: Methylation rate constants for water column and benthic segments (e.g., 1e-5 to 1e-2 day -1 )
- 11. MeHg Transformation Processes Photoreduction: MeHg to Hg(0) MeHg Constants: Set photolysis option (2), Quantum yield coefficients (1 for diss, sorb), Yield coefficient (0.93), Surface rate constant (e.g., 1e-3 to 1e-1) Parameters: Enter light attenuation coefficients for water column segments (e.g., 0.5-2 m -1 )
- 12. MeHg Transformation Processes Bacterial Demethylation: MeHg to HgII Constants: Set phase switches (1 for diss, sorb), Temperature correction factors (10 kcal/mole), Yield coefficient (0.93) Parameters: Enter demethylation rate constants for benthic segments (e.g., 1e-5 to 1e-2 day -1 )
- 13. HgII in Soil Tributaries reduction, evasion Atmospheric Wet and Dry Deposition reduction, volatilization Impervious Surface volatilization export export Water Surface runoff export runoff and erosion sediment layer MeHg Hg(II) Hg 0 Silt water column Sand WCS Watershed Model MDS Tributary Model Wasp5/6 Water Body Model Burial Leaching
- 14. Soil 74 μ g/kg Tributaries 12 μ g/m 2 -yr Atmospheric Deposition 12 (wet), 6 (dry) μ g/m 2 -yr 0.4 μ g/m 2 -yr Impervious Surface River 5 – 6 ng/L water column sediment layer 10 - 13 μ g/kg < 0.1 μ g/m 2 -yr 1.7 μ g/m 2 -yr 1.7 μ g/m 2 -yr Water Surface 0.6 μ g/m 2 -yr 0.2 μ g/m 2 -yr 0.2 % 1.3 % 3.4 % 95 % 1.3 μ g/m 2 -yr