Diffusive flux of selenium between lake sediment and overlying water: Assessing restoration alternatives for the Salton Sea

Abstract

Elevated concentrations of selenium are a concern for humans and wildlife at the Salton Sea, a large salt lake in the desert of southeastern California. As the lake is highly eutrophic and has become too saline for most fish, various restoration alternatives have been proposed. These would alter the water quality, volume, depth, and surface area of the Salton Sea and possibly create new aquatic habitats. Such changes are likely to alter conditions at the sediment-water interface that could influence the release or storage of selenium in the surficial, most bioavailable layers of lake sediment. A 5-day, 2×3 factorial laboratory experiment using intact cores of lake sediment with overlying lake water documented effects of dissolved oxygen level (oxic, anoxic) and salinity (2, 20, 35 g/L) on selenium flux. Higher positive flux from sediments into water was observed under oxic conditions and at the lowest salinity values. Selenium flux from the water to the sediment dominated at salinities of 20 and 35 g/L. Dissolved selenite (SeIV) and organic selenium compounds predominated in the overlying water. Results imply that selenium in overlying water is likely to be sequestered to the sediment under future highly saline conditions, as it is today, but may be released into the overlying water if its salinity is very low or if oxygenation is enhanced over current conditions.