CONTROLS ON SPATIAL VARIATION OF FISH MERCURY CONCENTRATIONS IN STREAMS OF THE ADIRONDACK REGION OF NEW YORK

The Adirondack Region is a circular uplifted area in northeastern New York underlain by metamorphic bedrock. The region is dominantly forested and characterized by abundant lakes, streams, and wetlands. The Adirondacks have been described as a hot spot of mercury (Hg) bioaccumulation and contamination, as reflected by region-wide warnings by the New York State Dept. of Health that recommend limits on human consumption of certain fishes from the region’s waters. The principal source of Hg to this region is atmospheric deposition from emissions at regional, continental, and global scales. Extensive forest cover, abundant wetlands, and aquatic ecosystems with low pH and low productivity are thought to contribute to the high levels of Hg bioaccumulation in aquatic food webs. The aim of this study is to describe spatial variation in fish Hg concentrations Adirondack streams and to explore the extent to which geochemistry and landscape factors can explain the observed patterns. We selected 35 streams to sample for major solutes and fish from among nearly 400 streams that were previously sampled in recent regional geochemical surveys. Hg concentrations were measured in brook trout (Salvelinus fontinalis), creek chub (Semotiluis atromaculatus), blacknose dace (Rhinichthyes atratulus) and central mudminnow (Umbra limi). Whole fish Hg concentrations from 63% of sites exceeded the 160 µg/g U.S. Environmental Protection Agency (USEPA) effects threshold for fish-eating wildlife, and estimated muscle concentrations from 60% of sites exceeded USEPA’s 300 µg/g advisory level for human consumption (despite the small size and low trophic position of most fish collected). Dissolved organic carbon concentrations (DOC) and pH were strong predictors of spatial variation in fish Hg concentrations among these streams. Ultra-violet absorbance (UVA) was an even stronger predictor of variation in fish Hg concentrations than DOC; UVA better reflects the ability of organic matter to complex and move Hg through the environment. Future analyses will focus on developing regression models that will provide predictions of expected levels of Hg in fish among the nearly 400 survey streams across the Adirondacks. Study results should prove helpful in determining the extent to which biota in Adirondack streams are impacted by Hg contamination.