Chemical evolution of shallow groundwater along the northeast shore of Mono Lake, California

We attempted to quantitatively discriminate between hypothesized sources and geochemical processes responsible for the chemical evolution of shallow groundwater along the northeast shore of Mono Lake, an alkaline saline lake located in a hydrologically closed basin in east central California. Shallow groundwater samples from 17 sites perpendicular and 11 sites parallel to the lakeshore were analyzed for major ions. The shallow groundwater contains remnant solutes from higher lake stands, which are transported toward the lake by lateral flow and surface runoff. The flow system appears to be segregated into two different regions: a concentrated, highly saline groundwater underlying much of the northeast shore and pockets of more localized lower-salinity groundwater. The saturation stare of the groundwater with respect to certain minerals was determined, and simulations for both evaporative concentration of inflow and mixing of lake water with inflow coupled with mineral precipitation were performed. Solute trends in the shallow groundwater result primarily from the degree of mixing with historical lake water; however, evaporative concentration and redissolution cycles along with various chemical fractionation mechanisms including Ca, Mg, and Na carbonate precipitation, sulfate reduction, ion exchange, and potentially Mg silicate formation are also important controls.