Modeling the Highly Dynamic Loading of Mercury Species in the Carson River and Lahontan Reservoir System, Nevada

The semiarid Carson River Lahontan Reservoir system in Nevada, United States is highly contaminated with mercury (Hg) from historic mining with contamination dispersed throughout channel and flood plain deposits. Work builds on previous research using a fully dynamic numerical model to outline a complete conceptualization of the system that includes transport and fate of both sorbed and dissolved constituents. Flow regimes are defined to capture significant mechanisms of Hg loading that include diffusion, channel pore water advective flux, bank erosion, and overbank deposition. Advective flux of pore water is required to reduce dilution and likely represents colloidal-mediated transport. Fluvial concentrations span several orders of magnitude with spatial and temporal trends simulated within 10-24% error for all modeled species. Over the simulation period, 1991-2008, simulated loads are 582 kg/yr (THg2+), 4.72 kg/yr (DHg2+), 0.54 kg/yr (TMeHg), and 0.07 kg/yr (DMeHg) with bank erosion processes the principal mechanism a loading for both total and dissolved species. Prediction error in the reservoir is within one-order of magnitude and considered qualitative; however, simulated results indicate internal cycling within the receiving reservoir accounts for only 1% of the reservoir's water column contamination, with river channel sediment sources more influential in the upper reservoir and bank erosion processes having greater influence in the lower reservoir.