Investigation of causal factors influencing mercury concentrations in fish tissues in five Nevada reservoirs

Mercury (Hg) concentrations in fish are of widespread concern due to human health risks. Recent data compiled by the Nevada Department of Wildlife showed Hg concentrations in fish muscle tissue that exceeded the human fish consumption advisory for several Nevada water bodies with no clear watershed source. To assess the reason for the elevated fish tissue concentrations this project focused on measuring Hg concentrations in fish, water, and sediments, and other relevant parameters, for five managed water bodies in northern Nevada: Ruby Lake, and Rye Patch, Chimney Dam, Wildhorse, and South Fork Reservoirs. The results of this study provide insight to potential parameters influencing fish Hg concentrations in rural Nevada water bodies. Chapter 2 of this thesis presents a discussion of the aquatic chemistry of these water bodies. These data showed that total Hg and MeHg concentrations in water and sediment were within the concentration range reported for uncontaminated systems with the exception of total Hg in Chimney Dam Reservoir and methylmercury (MeHg) in Ruby Lake. MeHg concentrations were highest in the winter months when samples were collected from under ice cover. Data collected in this study indicate that land- and atmospheric-based sources contribute to Hg loading to these water bodies. Chapter 3 examines Hg concentrations in biota from these water bodies and the relative importance of trophic position and water chemistry to Hg bioaccumulation. All five water bodies had fish with Hg concentrations exceeding the 0.3 mug/g EPA criterion value. Hg concentrations were greatest in fish of the highest trophic position as identified using N isotope ratios. Based on the data collected, bioaccumulation is the most important factor influencing fish Hg concentrations for the fish species and water bodies in this study.