DELINEATING POTENTIAL WATERSHED CONTRIBUTION TO MERCURY CONCENTRATION IN CADDO LAKE, HARRISON AND MARION COUNTIES, TEXAS

Caddo Lake has been included on the Texas Commission on Environmental Quality 303(d) list for impairment due to mercury content since 1995. One of the primary tributaries, Big Cypress Bayou, flows across Eocene-aged rocks and sediments associated with the Wilcox Formation; the Wilcox is of particular interest because it contains lignite coal, which has a direct link to mercury. Previous research has focused on fossil fuel combustion as the primary source of dry deposition mercury, but has not addressed the potential watershed contribution to mercury concentrations in Caddo Lake.

Big Cypress Bayou flows through Harrison and Marion counties in East Texas, and is one of the primary tributaries of the Caddo Lake watershed. The watershed covers approximately 164km²; the study area includes a 12 km segment of Big Cypress Bayou. Initial geochemical analyses will be conducted by collecting physicochemical parameters (temperature, pH, conductivity, dissolved oxygen, and turbidity) to determine areas in which the chemical environment may contribute to mobilization of mercury within the watershed. Data will be used for development of a comprehensive sampling scheme to determine if the geochemical conditions in Big Cypress Bayou are contributing to the mercury concentration in Caddo Lake.