Sensitivity of vertical mixing in a large saline lake to variations in runoff

Abstract

To examine the influences of changes in lake level and salinity on the seasonal mixing regime, we applied a one-dimensional vertical mixing model to Mono Lake, California. Assuming climate change leads to less precipitation in the Mono basin, we simulated the frequency and duration of meromixis for three hydrological scenarios in which precipitation and runoff were 100, 87.5, and 75% of those recorded for the 50-yr period from 1940 to 1990 with the assumption of no diversion of streamflow. Simulations indicate that Mono Lake would be susceptible to meromixis over a large range of lake levels for all three scenarios during very large runoff years. Climatic reconstructions and hydrological data also indicate a recent trend of higher interannual variability in precipitation and runoff in the Sierra Nevada. To assess the effect of higher interannual runoff variability on the frequency of meromixis in Mono Lake, we ran the 87.5 and 75% 50-yr freshwater inputs with no reductions in the eight largest runoff years. A higher incidence of meromixis was predicted when high runoff years were interspersed with drought periods that kept the lake at levels susceptible to long-term chemical stratification.