Grantee Research Project Results
Microbial Phylogenetic Diversity and Rates of Selenium Oxidation/Reduction in Response to Increasing Salinities in Littoral Sediments of the Salton Sea, CaliforniaEPA Grant Number: FP917272
Title: Microbial Phylogenetic Diversity and Rates of Selenium Oxidation/Reduction in Response to Increasing Salinities in Littoral Sediments of the Salton Sea, California
Investigators: Villa-Romero, Juan F
Institution: University of California - Berkeley
EPA Project Officer: Packard, Benjamin H
Project Period: August 1, 2011 through July 31, 2014
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2011) RFA Text | Recipients Lists
Research Category: Fellowship - Water Quality: Coastal and Estuarine Processes , Academic Fellowships
Objective:The Salton Sea is the largest inland body of water in California and is affected by elevated selenium concentrations in the sediments. Microbes control the geochemical cycle of selenium, which results in chemical species with different transport properties; salinity, on the other hand, is one of the factors controlling microbial diversity in the environment. In the next 15 years, the size of the Salton Sea is expected to shrink while water salinity increases. Consequently, submerged sediments would become gradually exposed to increasing salt concentrations and to atmospheric oxygen as the waterline of the lake recedes. The effect of these changes on microbial diversity has not been investigated for the Salton Sea, and neither their effect on the rates at which selenium is processed by indigenous microbial communities. This project focuses on littoral sediments of the Salton Sea and seeks to describe the effect of environmental change on biodiversity and on the functioning of ecosystem processes relevant to the geochemical cycle of selenium. More specifically, this study will investigate the phylogenetic diversity of microbial communities and the rates for selenium oxidation and reduction under a range of salinities that represent current and future scenarios for the Salton Sea. This study’s specific research objectives are to: (1) evaluate the correlation between detected changes in microbial diversity and in selenium transformation rates to determine the contribution of biodiversity to selenium cycling in the Salton Sea; and (2) characterize across a vertical depth gradient relevant physical, biological and geochemical properties in undisturbed sediment samples collected from Salton Sea littoral sites with recorded low, medium and high selenium concentrations to determine the contribution of these properties to selenium cycling in the lake.
Approach:Sediment slurries and flow-through reactors containing undisturbed sediment samples will be used to measure rates for selenium oxidation and reduction. The use of undisturbed sediments provides much more relevant data because sediment characteristics are maintained; these characteristics are abolished in slurry incubations. Phylogenetic diversity will be measured by evaluating 16s rRNA clone libraries and DNA microarray data obtained from DNA isolated onsite and at the end of geochemical experiments.
Given the low concentrations of soluble selenium in Salton Sea water, neither specialized pathways, nor selenium-specific microbes are expected to dominate selenium processing in littoral sediments of the Salton Sea. Instead, it is hypothesized that denitrifiers drive the dissimilatory reduction of selenium oxyanions in the lake. For the salinities tested, an increase in denitrification rates is expected as salinity increases due to the availability of electron donors and to the energetic requirements associated with life at elevated salt concentrations. An increase in reduction rates for selenium also is expected as salinity increases given the hypothesized relationship between denitrifiers and the reduction of selenium oxyanions. Following an exposure to atmospheric oxygen, selenium oxidation rates are not expected to change as salinity increases. In terms of microbial diversity, initially abundant groups are expected to dominate as salinities increase while less abundant ones become more rare or undetectable. Microbial groups associated with denitrification are expected in anaerobic samples under all tested salinities. Members of the Haloanaerobiales order of Archaea are expected to dominate communities exposed to anoxia and the highest salinity level. Aerobic or anaerobic conditions are expected to result in significantly different microbial communities; however, under both conditions halophilic Bacteria and Archaea are expected to predominate.
Potential to Further Environmental / Human Health Protection
Results from this investigation will provide restoration efforts targeting the recovery of the Salton Sea aquatic environment with information regarding the biogeochemical behavior of selenium under conditions expected to affect the lake in the near future. Today, elevated selenium concentrations in sediments of the Salton Sea represent a real threat to bird populations that include threatened and endangered species. In the 1980s, selenium was linked to mortality and developmental abnormalities in waterfowl in the Kesterson National Wildlife Refuge of the San Joaquin Valley in California. Furthermore, evaluating microbial diversity and specific geochemical reactions along a salinity gradient will contribute to the understanding of biodiversity, ecosystem functioning and their response to a changing environment.