EVAPORATIVE CONCENTRATION OF TRACE-ELEMENTS IN A MULTICELL AGRICULTURAL EVAPORATION POND

Evaporation ponds in California's San Joaquin Valley dispose of saline agricultural drainage waste water by evaporation. The waters comprise mainly Na, Cl, and SO4 but also may contain low levels of As, B, Mo, and Se. Evaporative concentration is of concern because Se bioaccumulation at Kesterson Reservoir, CA, has led to toxicosis in birds and fish. This project utilizes water quality data compiled from environmental monitoring of a multicell evaporation pond to observe accumulation characteristics of trace elements in pond waters. An evapoconcentration factor (ECF) is calculated from chloride concentrations and is assumed to reflect conservative behavior. Trace elements whose concentrations increase by the ECF are characterized as conservative, while others are labeled reactive, indicating the role of dissipation mechanisms. Conservative behavior characterizes B, while As is highly reactive. Both types of behavior are shown by Mo. Selenium was intermediately reactive, which may be due to a rate-limited removal mechanism.