Fish tissue metals and zooplankton assemblages of northeastern U.S. lakes

Abstract

Temperature, chlorophyll a, proportion of forest cover on the watershed, and fish tissue Pb, Zn, and Hg concentrations were the primary gradients that best explained the patterns of distribution of zooplankton assemblages in 38 northeastern U.S. lakes. Different zooplankton assemblages were associated with lakes that contained trout or cool-water species of minnows and systems dominated by a variety of warmwater fish species. Heavy metals in fish varied widely with geographic location and proximity to urban areas. Regression models indicated that Zn and Hg in fish were significantly and positively associated with chain length of the zooplankton web. In contrast, these metals and As showed a significant negative correlation with the number of feeding links between species. Structurally complex pelagic webs, comprising many lateral links, may significantly attenuate the transfer of heavy metals to higher trophic levels. Stepwise regression models that included structural variables significantly improved the amount of explainable variance in the fish metal concentrations over those with only physicochemical and land use variables. This study suggests that the high variability of metals in fish observed between adjacent lakes and across the region is explained in part by the structural features of the zooplankton web.