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Characterization of Mercury Transport and Fate in the Truckee River, NV, USA
AdvisorGustin, Mae S.
Natural Resources and Environmental Science
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The work described in this thesis provides a detailed investigation of mercury (Hg) distribution and the potential sources of methylmercury (MeHg) in fish for the Truckee River, CA-NV, USA. Mercury concentrations in biotic (fish and macroinvertebrates) and abiotic (water and sediments) components of the Truckee River were quantified along with a variety of other parameters to understand fish Hg concentrations and potential MeHg formation. Samples sites were chosen based upon the impacts of specific anthropogenic activities on river, water quality, and Hg bioavailability. Reaches of the river included sites above the city, within of cities of Reno-Sparks, below of the confluence with Steamboat Creek (SBC), a major contribution of non-point source of pollution, and below Derby Dam, the main obstacle in the river. The reach above the city may be characterized as a pristine river system and it was reflected in sediments, fish, and macroinvertebrate Hg concentrations. Even though within the city reach there were no significant differences in water quality and Hg concentrations with the reach above, fish d15N and d13C varied. Below SBC all sites were impacted most notably in nitrogen, phosphorous, sulfate, and Hg concentrations that increased in all abiotic and biotic components. The latter reach varied Hg concentrations by components. Derby Dam is an important factor influencing loads and concentrations by the diversion of water. Stable isotope ratios (d15N and d13C) in fish tissues showed that fish in higher position in the trophic levels had higher Hg concentrations and as well as the anthropogenic inputs of these elements into the river. Temporally and spatially, higher values for water quality parameters and water Hg and MeHg concentrations and loads were found during spring, when the flows was the highest indicating that in these conditions Hg was mobilized and transported down river. Fish Hg concentrations ranged from below detection to 0.94 µg/g (wet weight) with general increasing trends down river. Trends of MeHg in filtered water and in a suite of macroinvertebrates were correlated with that observed for fish increasing trends down river in this flowing water system. In conclusion, mercury derived from legacy mining in the late 1800's continues to be transported from Steamboat Creek to the Truckee River. This Hg is mostly deposited to the shore of the river where it may be methylated and become available to biota in the river. During periods of higher flow MeHg and other forms of Hg are input to the water column and transported downstream.