Modeling Drainwater Selenium Removal in Wetlands

Abstract

Prediction of selenium (Se) mass distribution and Se speciation in wetlands is desired for a comprehensive assessment of the capability of vegetated wetlands to remove Se from agricultural drainage waters prior to impoundment in evaporation basins. A mathematical model was developed to describe Se transformations and transport in Tulare Lake Drainage District’s pilot flow-through wetland cells in California having dimensions of 15 m width and 76 m length. In the model, the wetland cell is subdivided into five subcells and each subcell consists of 10 internal compartments and Se can be transferred between the compartments by physical and chemical processes. Physical processes include water movement, plant litter drop, and physical material breakdown. Chemical processes include Se reduction from selenate (SeVI) to selenite (SeIV), and further reduction to elemental selenium (Se0) and organic Se (Se-II). In the chemical processes, the Se transformation reaction was assumed to obey first-order kinetics and the Arrhenius equation for temperature dependency. A total of 33 ordinary differential equations were written to describe all the processes within and between the internal compartments. A