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An Examination of the Factors that Control Methylmercury Production and Bioaccumulation in Maryland Reservoirs Draft Final Report June, 2006. Cynthia C. Gilmour Smithsonian Environmental Research Center Edgewater, MD 21032 Robert P. Mason Dept. Marine Sciences University of Connecticut

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An Examination of the Factors that Control Methylmercury Production and Bioaccumulation in Maryland ReservoirsDraft Final ReportJune, 2006

Cynthia C. Gilmour

Smithsonian Environmental Research Center

Edgewater, MD 21032

Robert P. Mason

Dept. Marine Sciences

University of Connecticut

Groton, CT 06340

Andrew Heyes

Chesapeake Biological Laboratory

University of Maryland, Center for Environmental Science

Solomons, MD, 20688

Mark Castro

Appalachian Laboratory

University of Maryland, Center for Environmental Science

Frostburg, MD 21532

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What drives the differences in MeHg in fish among Maryland reservoirs?

What can be done to limit MeHg bioaccumulation in Maryland?

EPA’s Ambient Water Quality Criterion (AWQC) for Hg in fish tissue is 235 ug/kg

Mercury concentrations in largemouth bass in Maryland reservoirs, size-normalized to a 370 mm fish (data from Gilmour et al. “An Examination of the Factors that Control Methylmercury Production and Bioaccumulation in Maryland Reservoirs” MD DNR in review).

parameters used to examine controls on hg in maryland fish
Parameters used to examine controls on Hg in Maryland fish

Factors that influence MeHg bioaccumulation:

Water chemistry

MeHg, pH, DOC, TSS, nutrients

Deposition

Transport

Deposition

Watershed retention

Bioaccumulation

Factors that affect Hg deposition and transport:

Watershed size

Watershed:lake area

Landuse

Physiographic province

Reservoir capacity

Hydraulic residence time

Water chemistry

Sediment

Methylation

Factors that affect net methylation:

Water chemistry

Hg, pH, sulfate, DOC, conductivity, DO, TSS, nutrients

Sediment chemistry

Pore waters: Hg, pH, sulfate, sulfide, Fe, Mn, DOC

Bulk phase: Hg, density, organic matter, reduced sulfur (AVS/CRS)

Sediment water partitioning

statistical analysis
Statistical Analysis

Three separate models:

  • Factors that affect Hg deposition and transport:
    • Dependant variable: Hg in water and sediments
  • Factors that affect net methylation:
    • Dependant variable: MeHg in water and sediments
  • Factors that influence MeHg bioaccumulation:
    • Dependant variable: BAF (MeHg in Largemouth bass: MeHg in water)

Stepwise multiple regression

significant parameters in each model component
Significant parameters in each model component

Factors that influence MeHg bioaccumulation:

Dependant variable: BAF

DO (-), pH (+), surface:volume ratio (+)

Deposition

Transport

Deposition

Watershed retention

Bioaccumulation

Methylation

Factors that affect Hg deposition and transport:

Dependant variable: Hg in water and sediments

Hg deposition (+)

Landuse: % developed (+)

Water chemistry: Cl, DOC (+)

Sediment: organic content (+)

Reservoir flow (-), water depth (-)

Factors that affect net methylation:

Dependant variable: MeHg in water and sediments

Water chemistry

Hg (+), pH (-), sulfate (+), DO (-)

Sediment chemistry

Hg (+), sulfide (-), organic matter (+)

slide8

Watershed factors: Hg deposition

From MD DNR (Sherwell) 2006

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Methylation: %MeHg as the dependant variable

Varies strongly among reservoirs

significant parameters in each model component1
Significant parameters in each model component

Factors that influence MeHg bioaccumulation:

Dependant variable: BAF

DO (-), pH (+), surface:volume ratio (+)

Deposition

Transport

Deposition

Watershed retention

Bioaccumulation

Methylation

Factors that affect Hg deposition and transport:

Dependant variable: Hg in water and sediments

Hg deposition (+)

Landuse: % developed (+)

Water chemistry: Cl, DOC (+)

Sediment: organic content (+)

Reservoir flow (-), water depth (-)

Factors that affect net methylation:

Dependant variable: MeHg in water and sediments

Water chemistry

Hg (+), pH (-), sulfate (+), DO (-)

Sediment chemistry

Hg (+), sulfide (-), organic matter (+)

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