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Mercury Mass Balance Modeling in Lake Ontario

Mercury Modeling Workshop, Niagara Falls, NY January 19-20, 2006. Mercury Mass Balance Modeling in Lake Ontario. Joseph Atkinson, James Jensen University at Buffalo Joseph V. DePinto Limno-Tech, Inc. Presentation Outline.

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Mercury Mass Balance Modeling in Lake Ontario

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  1. Mercury Modeling Workshop, Niagara Falls, NY January 19-20, 2006 Mercury Mass Balance Modeling in Lake Ontario Joseph Atkinson, James Jensen University at Buffalo Joseph V. DePinto Limno-Tech, Inc.

  2. Presentation Outline • Background and overview of Lake Ontario Mass Balance Modeling in Support of LaMP • LaMP modeling needs • LOTOX2 development and application • Mercury modeling under LOADS • Development of Hg sub-model for LOTOX2 • Preliminary application for available data analysis • Recommendations for future work

  3. Lake Ontario Lakewide Management Plan (LaMP) • GLWQA mandated Lakewide Management Plan (LaMP) in all Great Lakes • Lake Ontario LaMP led by Four Party Secretariat • EPA-Region 2, NYS DEC, Environment Canada, Ontario MOE • Resolve lakewide beneficial use impairments as defined in GLWQA • Restrictions on fish consumption • Degradation of wildlife populations • Bird or animal deformities or reproductive problems • Loss of fish and wildlife habitat • LOTOX2 model develop to help address several management questions for critical pollutants in Lake Ontario

  4. PCBs, chlordane, DDT & metabolites, dieldrin, toxaphene, 2,3,7,8-TCDD-PCDF, mercury, mirex-photomirex, hexachlorobenzene, octochlrostyrene, benzo(a)pyrene, lead, heptachlor/heptachlor epoxide Chemicals of Concern for Lake Ontario ortho meta Cl Cl Cl para Cl 2,2',3,4' - Tetrachlorobiphenyl Typical Toxic Substance is: • Hydrophobic • Persistent • Semi-volatile • Bioaccumulative

  5. Toxic Chemical Questions for Lake Ontario Lakewide Management Plan (LaMP) • What is the relative significance of each major source class discharging toxic chemicals into Niagara R. and Lake Ontario? • What is the role of toxic chemicals existing in sediments of the system? • Can changes in major source categories and sediments be quantitatively related to concentrations in the water column and fish? • Can observed trends in toxic chemical concentrations over time be explained? • How does a regulatory or remediation action affect the water column and fish tissue concentrations at steady-state and over time?

  6. EPA-Funded Lake Ontario Modeling Projects • Long-term plan (UB-NYGLRC) • Funded by EPA-Region 2 • 1996-1997 • LOTOX2 Development and Improvement (UB-NYGLRC) • Funded by EPA-Region 2 • Two project periods for plan implementation • 1997-2000 • Development of LOTOX2 into management tool (LTI) • Funded by EPA-Region 2 • 2002-2004 • Linked hydrodynamic-LOTOX2 model (UB/LTI) • Funded by EPA-GLNPO • 2002-2003 • Modeling for LOADS (UB/LTI) • Funded by EPA-Region 2 • 2002-2005 • LOTOX2 PCB Model application for TMDL (UB/LTI) • Funded by EPA-Region 2 through GLNPO call • Starts January 2006

  7. Modeling Approach • Develop LOTOX2 model (Improve spatial and temporal resolution) • Construct spatially-resolved Solids Dynamics Model • Long term 137Cs time-dependent mass balance • Calibrate solids dynamics with 137Cs tracer • Reconstruct historical PCB loadings • Calibrate LOTOX2 with historical PCB data • Confirmation of LOTOX2 • Apply LOTOX2 to forecast lake response to load reduction actions

  8. Information Flow in LOTOX2 Model In situ Solids Levels Hydraulic Transport (POM) Sorbent Dynamics Model Chemical Mass Balance Model Food Chain Bioaccumulation Model Chemical Loading LOTOX2 - Time-dependent, spatially-resolved model relating chemical loading to concentration in water, sediments and adult lake trout

  9. LOTOX2 Chemical Mass Balance Framework Atmospheric wet & dry deposition Gas phase absorption Volatilization Niagara river Total toxicant in water column Outflow Hamilton Harbor desorption Toxicant on suspended particulates Toxicant in dissolved form US tributaries Water Column Canadian tributaries sorption Decay US direct sources diffusive exchange resuspension Canadian direct sources settling Total toxicant in sediment desorption Toxicant on sediment particulates Dissolved toxicant in interstitial water Decay Surficial Sediment sorption Deep Sediment burial

  10. LOTOX2 Segmentation Scheme - plan view N Surface water column Deep water column Surface sediment Projection of water column to sediment segments

  11. Toxicant Concentration in Phytoplankton (mg/g) (1) Toxicant Concentration in Zooplankton (mg/g) (2) Toxicant Concentration in Small Fish (mg/g) (3) Toxicant Concentration in Large Fish (mg/g) (4) Bioaccumulation Model Framework Predation Depuration Depuration Depuration Depuration Uptake Uptake Uptake Uptake “Available” (Dissolved) Chemical Water Concentration (ng/L) Physical-Chemical Model of Particulate and Dissolved Concentrations

  12. Model Calibration/Confirmation - Lake Trout PCB

  13. Baseline and Categorical Scenarios(all scenarios start at 2000 and run for 50 years)

  14. LOTOX2 Findings for Management of PCBs in Lake Ontario • Significant PCB load reductions from mid-60s through mid-90s • Significant open water and lake trout declines through 70s and 80s • Slower declines in open waters through ‘90s due largely to sediment feedback • Lake trout PCBs not yet at steady-state with current loads. Time to approximate steady-state with 1995 loads is ~30 years. • Ongoing load reductions are slower • Point Sources of PCBs are small fraction of current total loading but may have localized benefits • PCBs in lake trout are already below the New York State guidelines for “eat none” of 1.9 ppm • LOTOX2 forecasts suggest that we will not be able to achieve unrestricted lake trout consumption, based on the uniform Great Lakes protocol (0.05 ppm), without virtually eliminating watershed PCB loads and seeing some reduction in atmospheric deposition loading as well

  15. Mercury Model development to enhance LOTOX2 capabilities to analyze LaMP priority pollutantsin Lake Ontario

  16. Hg Modeling Approach • Develop Hg Sub-model • Develop conceptual model for Hg in Lake Ontario • Write mass balance equations for each state variable • Conduct literature review to develop initial model parameterization • Preliminary analysis – sensitivity and data needs • Incorporate Hg Sub-Model into LOTOX2 • Uses same water and solids transport • Extend number of state variables (4 for Hg, instead of 1, as for PCBs) • Include Hg chemical reactions (not just first order) • Modify interphase mass transfer functions (species specific) • Compile loading and boundary condition data • Uses data from LOADS and literature • Conduct model testing and preliminary calibration to available in-lake data • Conduct diagnostic analysis to identify and prioritize additional data needs

  17. Conceptual model : Non-equilibrium reaction : Equilibrium reaction : Exchange : Settling and Burial : State variables Deposition Atmosphere Volatilization Volatilization Loading Outflow Epilimnion Hg(0) Bioaccumulation Hg(II) solids Hg(II) MMHg Bio-Hg DMHg Hg(0) Hypolimnion Bioaccumulation Hg(II) solids Hg(II) MMHg Bio-Hg DMHg Sediment Hg(II) solids Hg(II) MMHg DMHg Burial (3 sediment layers)

  18. Bioaccumulation Bioconcentration (direct uptake) Phytoplankton 1 Zooplankton 2 Small Fish 3 Large Fish 4 MMHg Biomagnification Same framework as for PCBs – parameterized for lake trout in 4th level Physical-chemical model of (particulate and) dissolved concentrations

  19. Data • Much uncertainty in loading data • “Preliminary” loading estimates from 2004 Lake Ontario LaMP: • Upstream: 75% • Point discharges: 10% • Atmospheric deposition: 10% • Tributaries: 5% • “No estimations” of discharge via St. Lawrence River or volatilization (2004 Lake Ontario LaMP)

  20. Summary

  21. Sensitivity Analysis • Focus on methylation/demethylation rates • Widest range in reported values • Expected impact on model results most uncertain • Variations expected on site-specific basis

  22. Variation in methyl Hg with k1_H hypolimnion epilimnion

  23. Summary • Besides MMHg, little sensitivity found • For MMHg, strong sensitivity to both k1 and k2, especially in the hypolimnion • Other processes more important in epilimnion • Steady state reached for water column concentrations of Hg(0) and Hg(II) after 1 – 2 years • Steady water column concentrations of MMHg were reached after about 10 years • Sediment concentrations for all species approached steady values only for times approaching 70 years

  24. Ongoing and Future Work • Continue testing LOTOX2 with incorporated Hg submodel • Recalibrate Hg bioaccumulation portion of the model • Long-term runs with variable loading (atmospheric, tributary) – similar to PCB runs • Determine extent to which steady conditions exist in the lake • Evaluate relative impacts of different sources • Continue data collection and site-specific Hg process experimentation

  25. Questions and Discussion

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