Submitted to: Proceedings of the International Salinity Forum
Publication Type: Abstract Only
Publication Acceptance Date: 2/3/2005
Publication Date: 4/25/2005
Citation: Herbel, M.J., Gao, S. and Johnson, T. 2005. Selenium transformations in salinity-affected agricultural drainage water management areas of California as determined by selenium stable isotope ratios. In: Proceedings of the International Salinity Forum, Managing Saline Soils and Water: Science, Technology, and Soil Issues. April 25-27, 2005. Riverside, CA pp: 231-234. Interpretive Summary:
Technical Abstract: The trace element selenium (Se) is of high concern in the Western San Joaquin Valley of California. Evapoconcentration of irrigation drainage water has increased Se concentrations in soils, sediments, and shallow ground waters, which has posed a significant risk to wildlife. To decrease the effects of salinity and detrimental impact of Se on irrigated agriculture and wildlife, various management strategies have been tested and/or implemented. For example, saline drainage waters have been used on more salt-tolerant plants, impounded in evaporation basins, or passed through vegetated wetlands to facilitate removal of hazardous trace elements. Predicting the behavior (speciation), transport, and fate of Se in these drainage water management regions is challenging due to the ability of Se to exist in multiple oxidations states (VI, IV, O, and -II) and in various inorganic and organic forms. In this investigation, Se stable isotope ratios (80 Se/76 Se) are measured and used to characterize and predict Se transport and biogeochemical cycling. Various water, soil and plant samples were collected from the experimental Tulare Lake Drainage District (TLDD) flow-through wetland (1996-2001), which was used as a model system to understand the dynamics of Se after it enters the wetland as Se(VI) in agricultural drainage water. Selenium stable isotope ratio analysis revealed that, for this management system, the major transformation pathway for aqueous Se(VI) was plant uptake from the water column followed by deposition of the plant material and mineralization of the organic Se to Se(O). This study has demonstrated that Se stable isotope ratios can similarly be used to elucidate Se sources and transformation pathways in other salinity-affected regions.