Regional drivers of fish tissue mercury concentrations in the Great Plains, USA

Abstract

Abstract Mercury, a highly toxic metal, is deposited onto land from the atmosphere through wet and dry deposition, and can be transported into waterways. In lakes and streams, mercury bioaccumulates and then biomagnifies in sediments and aquatic food webs. Thus, mercury from food web sources can be biomagnified in fish tissue, and humans can be exposed through consuming contaminated fishes. Several biological, chemical, and physical factors influence the concentration of mercury in fish tissues, such as species identity, and watershed land use. We accessed publicly available fish tissue mercury data for six states in the Great Plains, USA (Iowa, Kansas, Missouri, Minnesota, Nebraska, and South Dakota), and linked them to watershed characteristics such as land use. We used mixed-effect regression analysis and model selection approaches to test the prediction that the presence of wetlands and agriculture in the watershed increases the mercury concentration found in fish tissue. Fish tissue mercury depended on species identity foremost and secondarily on spatial variables (e.g. land use/land cover, state). Presence of wetlands and mixed-forest habitat in the watershed increased fish tissue mercury concentration, but other land uses showed weaker relationships. Overall, our results emphasized the importance of species traits in predicting fish tissue mercury concentrations. Analysis of watershed land use and land cover variables also explained variation in fish contamination, highlighting the importance of watershed-scale parameters in evaluations of mercury exposure from wild-caught fish.