MERCURY IN BIG CYPRESS BAYOU AND CADDO LAKE WATERSHEDS IN MARION AND HARRISON COUNTIES TEXAS

Caddo Lake has been included on the Texas Commission on Environmental Quality 303(d) list for impairment due to mercury (Hg) content since 1996. One of the primary tributaries, Big Cypress Bayou, flows across Eocene-aged rocks and sediments associated with the Wilcox Group; the Wilcox is of interest because it contains lignite coal, which has a direct link to mercury. Previous research has focused on dry deposition from fossil fuel combustion as the primary source of 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 15km segment of Big Cypress Bayou. Initial geochemical analyses were conducted by collecting physicochemical parameters to determine the chemical environment that may contribute to mobilization of mercury within the watershed. These data were used to develop a comprehensive sampling scheme to determine if the geochemical conditions present in Big Cypress Bayou are contributing to the mercury concentration in Caddo Lake. The results provided insight into the spatial and temporal distribution of mercury in the study area and areas of interest for future studies regarding mercury mobilization in the watersheds. This study also identified other areas that may be contributing to the unique geochemical environment of the Caddo Lake watershed.