Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 8/1/2013
Publication Date: 12/1/2013
Citation: Gao, S., Chang, A. 2013. Chapter 8. Chemical and biological processes of evaporation ponds. In A. Chang and D.B. Silva (Eds.) Salinity and Drainage in San Joaquin Valley, California Science, Technology and Policy. New York, NY. Springer, p. 185-210. Interpretive Summary: Agricultural evaporation ponds are commonly used to dispose agricultural drainage in the hydrologically closed Tulare Basin and some areas of the Westside of the San Joaquin Valley of California. This paper summarizes research finding on the chemistry of the evaporation ponds including salt and toxic trace element accumulation and processes/conditions affecting their transformations. Findings indicate that salt precipitation, selenium, and arsenic chemistry are well understood and information on chemical transformation of other trace elements including molybdenum, vanadium and uranium is rather limited. This review provides information for drainage water management and potential concerns to address for sustainable agricultural production in the area.
Technical Abstract: Agricultural evaporation ponds are designed to impound and dissipate saline agricultural drainage water in areas with no opportunities for offsite disposal in the San Joaquin Valley of California. This paper reviews and summarizes research findings on the pond chemistry. Drainage waters in these ponds are desiccated by evaporation resulting in elevated levels of dissolved mineral salts and trace elements (chiefly B, Se, As, Mo, U, and V) as well as precipitation of evaporite minerals. Redox conditions control transformation of trace elements. Salinity and evapoconcentration factors (ECF), major soluble ions, dissolved organic carbon and reduced species of trace elements increase along the water flow path. Boron in pond waters increases linearly with evaporation. Selenium is subject to strong sink mechanisms to immobilize Se from water to sediments from reduction of selenate to selenite, elemental Se and organic Se, resulting in lower Se concentrations than the inlet drainage water in evaporation pond waters in the hydrologically close Tulare Basin. Arsenic immobilization is also apparent causing accumulation in sediments but sink mechanisms are not significant enough to reduce As concentrations in pond waters as shown by a positive correlation between salinity and As concentration. Direct information on speciation and transformation data for Mo, U, and V in evaporation ponds is limited. Total concentration changes in pond waters and sediment incubation studies indicate that they are all subject to reduction and immobilization under reducing environment.