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 Robert P. Mason Dept. Marine Sciences University of Connecticut Groton, CT Andrew Heyes Chesapeake Biological Laboratory University of Maryland, Center for Environmental Science Solomons, MD, Mark Castro Appalachian Laboratory University of Maryland, Center for Environmental Science Frostburg, MD 21532

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). 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

Parameters used to examine controls on Hg in Maryland fish Factors that affect Hg deposition and transport: Watershed size Watershed:lake area Landuse Physiographic province Reservoir capacity Hydraulic residence time Water chemistry Sediment 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 Factors that influence MeHg bioaccumulation: Water chemistry MeHg, pH, DOC, TSS, nutrients Deposition Transport Watershed retention Deposition Methylation Bioaccumulation

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 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 (+) Factors that influence MeHg bioaccumulation: Dependant variable: BAF DO (-), pH (+), surface:volume ratio (+) Deposition Transport Watershed retention Deposition Methylation Bioaccumulation

Watershed factors: Hg deposition

From MD DNR (Sherwell) 2006 Watershed factors: Hg deposition

Watershed factors: Landuse

Methylation: %MeHg as the dependant variable Varies strongly among reservoirs

Controls on methylation: bottom water anoxia

Controls on methylation: pH Sulfate

Significant parameters in each model component 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 (+) Factors that influence MeHg bioaccumulation: Dependant variable: BAF DO (-), pH (+), surface:volume ratio (+) Deposition Transport Watershed retention Deposition Methylation Bioaccumulation