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Impact of Potential Climate Change on Predicted Fluvial Transport of Mercury and Associated Bioaccumulation along the Carson River-Lahontan Reservoir
AdvisorCarroll, Rosemary WH
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Historic mining practices have left the Carson River and Lahontan Reservoir (CRLR) system contaminated with high levels of mercury (Hg). Hg levels in Lahontan Reservoir planktivorous and predatory fish exceed federal human consumption limits. Inputs of Hg to the system are a result of contaminated bank erosion during high flow and diffusion from contaminated bottom sediments during low flow. The United States Bureau of Reclamation has produced future streamflow estimates for 2000-2099 using 112 CMIP3 climate projections and the Variable Infiltration Capacity (VIC) model. VIC results suggest that the hydrology of the system is likely to experience increased frequency of both high and low extreme flows, and the monthly averages of future flows are expected to be higher in the winter and lower in the summer compared to historical simulated flows. The VIC streamflow projections and modeled reservoir outputs are prepared as input for a Hg transport model, which consists of three numeric codes dynamically coupled (RIVMOD, WASP5, and MERC4). The dissolved methylmercury (MeHg) simulated from these models runs are used as input for a bioenergetics and mercury mass balance model (BioHg) which computes the bioaccumulation of MeHg in Sacramento blackfish in the Lahontan Reservoir. Model results suggest that loads of total Hg, total MeHg, and dissolved MeHg will decrease most significantly in the spring and summer due to the channel width increases and the depth decreases which reduce bank erosion over the century. Dissolved Hg loads increase in both the winter and spring, but decrease in the summer. An increase in channel bottom area leads to a higher rate of diffusive flux of dissolved Hg. Bioaccumulation levels may increase in both the South and Middle Basins of the reservoir as a result of an increase in dissolved MeHg concentrations, but decrease in the North Basin due to mercury settling out in the upstream sections of the reservoir and the dilution effect of the Truckee Canal input near the Lahontan Dam. All three sections of the reservoir will maintain fish Hg levels above the federal action limit for consumption.