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Abstract. As part of an initiative to assemble and synthesize mercury (Hg) data from environmental matrices across northeastern North America, we analyzed a large dataset comprised of 15,305 records of fish tissue Hg data from 24 studies from New York State to Newfoundland. These data were summarized to provide mean Hg concentrations for 40 fish species and associated families. Detailed analyses were carried out using data for 13 species. Hg in fishes varied by geographic area, waterbody type, and waterbody. The four species with the highest mean Hg concentrations were muskellunge (Esox masquinongy), walleye (Sander vitreus), white perch (Morone americana), and northern pike (Esox luscius). Several species displayed elevated Hg concentrations in reservoirs, relative to lakes and rivers. Normalized deviations from mean tissue levels for yellow perch (Perca flavescens) and brook trout (Salvelinus fontinalis) were mapped, illustrating how Hg concentrations in these species varied across northeastern North America. Certain geographic regions showed generally below or above-average Hg concentrations in fish, while significant heterogeneity was evident across the landscape. The proportion of waterbodies exhibiting exceedances of USEPA's criterion for fish methylmercury ranged from 14% for standard-length brook trout fillets to 42% for standard-length yellow perch fillets. A preliminary correlation analysis showed that fish Hg concentrations were related to waterbody acidity and watershed size.

Abstract. Whereas many ecosystem characteristics and processes influence mercury accumulation in higher trophic-level organisms, the mercury flux from the atmosphere to a lake and its watershed is a likely factor in potential risk to biota. Atmospheric deposition clearly affects mercury accumulation in soils and lake sediments. Thus, knowledge of spatial patterns in atmospheric deposition may provide information for assessing the relative risk for ecosystems to exhibit excessive biotic mercury contamination. Atmospheric mercury concentrations in aerosol, vapor, and liquid phases from four observation networks were used to estimate regional surface concentration fields. Statistical models were developed to relate sparsely measured mercury vapor and aerosol concentrations to the more commonly measured mercury concentration in precipitation. High spatial resolution deposition velocities for different phases (precipitation, cloud droplets, aerosols, and reactive gaseous mercury (RGM)) were computed using inferential models. An empirical model was developed to estimate gaseous elemental mercury (GEM) deposition. Spatial patterns of estimated total mercury deposition were complex. Generally, deposition was higher in the southwest and lower in the northeast. Elevation, land cover, and proximity to urban areas modified the general pattern. The estimated net GEM and RGM fluxes were each greater than or equal to wet deposition in many areas. Mercury assimilation by plant foliage may provide a substantial input of methyl-mercury (MeHg) to ecosystems.

The northeastern USA receives some of the highest levels of atmospheric mercury deposition of any region in North America. Moreover, fish from many lakes in this region carry Hg burdens that present health risks to both human and wildlife consumers. The overarching goal of this study was to identify the attributes of lakes in this region that are most likely associated with high Hg burdens in fish. To accomplish this, we compared data collected in four separate multi-lake studies. Correlations among Hg in fish (4 studies) or in zooplankton and fish (2 studies) and numerous chemical, physical, land use, and ecological variables were compared across more than 150 lakes. The analysis produced three general findings. First, the most important predictors of Hg burdens in fish were similar among datasets. As found in past studies, key chemical covariates (e.g., pH, acid neutralizing capacity, and SO4) were negatively correlated with Hg bioaccumulation in the biota. However, negative correlations with several parameters that have not been previously identified (e.g., human land use variables and zooplankton density) were also found to be equally important predictors. Second, certain predictors were unique to individual datasets and differences in lake population characteristics, sampling protocols, and fish species in each study likely explained some of the contrasting results that we found in the analyses. Third, lakes with high rates of Hg bioaccumulation and trophic transfer have low pH and low productivity with relatively undisturbed watersheds suggesting that atmospheric deposition of Hg is the dominant or sole source of input. This study highlights several fundamental complexities when comparing datasets over different environmental conditions but also underscores the utility of such comparisons for revealing key drivers of Hg trophic transfer among different types of lakes.