Spatial Trends and Factors Affecting Mercury Bioaccumulation in Freshwater Fishes of Washington State, USA

Twenty-four lakes in Washington State, United States, were sampled for largemouth and smallmouth bass as well as water chemistry parameters during 2005 to 2009 to evaluate trends in mercury (Hg) concentrations. We analyzed spatial patterns in bass Hg levels across a gradient of land and climate types, lake chemistry parameters, and physical watershed characteristics to identify factors influencing Hg bioaccumulation. Across the state, bass Hg levels followed rainfall patterns and were statistically greater on the coastal west side of the state and lowest in the drier eastern region. Lake and watershed variables with the strongest correlations to Hg bioaccumulation in bass were annual watershed precipitation (+) and lake alkalinity (-). Principal component analysis (PCA) explaining 50.3 % of the variance in the dataset indicated that wet, forested landscapes were more likely to contain lakes with greater fish Hg levels than alkaline lakes in drier agriculture-dominated or open space areas. The PCA did not show wetland abundance and lake DOC levels as variables influencing bass Hg levels, but these were generally associated with small, shallow lakes containing greater chlorophyll levels. The effect of in-lake productivity may have counteracted the role of wetlands in Hg bioaccumulation among this study's lakes.