Effects of increasing salinity and redox oscillation on selenium cycling and phylogenetic diversity in littoral sediments of the Salton Sea

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The Salton Sea, located in the desert area of southeastern California, is the largest lake in the state. It is a shallow, eutrophic and hypersaline lake whose shoreline is currently at an elevation of more than 70 m below sea level. Because the Salton Sea has no outlets and is located in an arid region of high evaporation, it has been accumulating soluble salts in its water and insoluble constituents in its bottom sediment for nearly 100 years, reaching a current salinity a third higher than seawater. Selenium (Se) is among the constituents that, in addition to water salinity, threaten the health of the Salton Sea.

The Salton Sea is an ecological disaster that may not attract the attention and investment needed to avoid catastrophic impacts to public health and to the millions of birds the lake supports (Cohen, 2008). The Salton Sea will change dramatically in the near future, whether or not officials take action on its behalf. The various restoration actions proposed, including the “no-action alternative” (Cohen and Huyn, 2006) would all results in similar changes at the Salton Sea. Salinity will increase and the surface of the lake will drop, due to a decrease in inflows to the lake. The uptake and bioaccumulation of Se by primary producers would likely increase because of higher Se concentrations entering the system from tributaries and drains (U.S. Department of Interior, 2007). Bottom sediment from medium water depths is higher in Se than from shallower depths, and this sediment would be exposed to more oxic conditions than generally prevail at shallower depths, increasing the possible oxidation, and consequently remobilization, of Se. The objectives of our research are to characterize selenium cycling at the sediment-water interface under conditions of increasing salinities, and switch from anoxic/suboxic to oxic conditions and to correlate the geochemistry of selenium with the changes observed in microbial community structure to identify the particular taxonomic groups driving Se geochemistry.

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