Impact of Climate Change on Mercury Transport along the Carson River-Lahontan Reservoir System

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 consumption limits. Inputs of Hg to the system are mainly a result of erosion during high flow and diffusion from sediment during low flow, and the relationships between streamflow and both mercury transport and bioaccumulation are non-linear. 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 higher frequencies 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 observed flows. VIC daily streamflow estimates are biased-corrected using an empirical cumulative distribution function to match observed data over the historic period of 1950-1999. Future reservoir stage and outflows are modeled assuming reservoir operations are a function of river/canal inflows, previous reservoir stage and downstream agricultural demands. VIC and reservoir flows drive the CRLR Hg transport model (RIVMOD, WASP5, and MERC4). Daily output for both total and dissolved inorganic Hg and methylmercury (MeHg) are averaged at the decadal timescale to assess changes and uncertainty in predicted spatial and temporal Hg species water column concentrations as a function of altered hydrology with respect to changing climate. Future research will use CRLR output in a bioenergetics and Hg mass balance model for Sacramento blackfish (Orthodon microlepidotus), a filter feeding cyprinid found in Lahontan Reservoir. These future simulations will help to assess possible changes in ecosystem health with respect to hydrologic conditions and associated changes to Hg transport.