Geochemistry of a large impoundment, Part I: solute sources, mixing dynamics, and seasonal anoxia

Lake Texoma is a large impoundment on the border of Texas and Oklahoma, formed from the confluence of two river systems with different salinities, the Red River (total dissolved salt, TDS, of 2700–11 900 mg/l, average of 4862 mg/l) and the Washita River (TDS of 420–915 mg/l, average of 701.4 mg/l). Systematic analyses for major and trace elements were conducted of water samples collected spatially and with depth in the lake in different seasons. Overall, Lake Texoma waters are characterized by Na-Ca-Cl-SO₄-type waters with spatial distribution shifting from Na-Cl type to Ca-SO₄ type from the Red River arm to the main lake and to the Washita River arm. In addition, vertical and seasonal variations in major and trace elements concentrations indicate major elements in the lake are mainly controlled by different bedrock weathering from the two river systems. Trace elements that exhibit different distribution patterns to the major species are associated with variable sources such as river inflow, summer stratification effects, biological effects and anthropogenic activities. In Lake Texoma, differential inflow volumes and summer stratification are principal factors controlling the variation and geochemistry of lake waters and mixing dynamics.