HEAVY METAL CONCENTRATIONS IN BIG CYPRESS AND BLACK CYPRESS BAYOUS, CADDO LAKE WATERSHED, TEXAS

Big Cypress and Black Cypress bayous are primary tributaries of Caddo Lake watershed in eastern Texas. The confluence of these tributaries occurs approximately 6km east of Jefferson, Texas in Marion County. The watershed is underlain by Eocene-aged strata from the Wilcox and Claiborne groups, which represent transgressive/regressive shoreline fluctuations that deposited interbedded friable sandstones and mudstones. The Wilcox Group is of special interest because it contains lignite coal, which has a direct link to some heavy metals. Caddo Lake has been listed on the Texas Commission on Environmental Quality 303(d) list for impairment due to mercury in edible tissue since 1995 and Black Cypress Bayou has been listed for impaired waters due to elevated copper since 2010.

During 2016 and 2017, water samples and sediment samples from locations along these tributaries were analyzed for heavy metal concentrations. Physiochemical parameters of water samples (temperature, pH, conductivity, dissolved oxygen, and turbidity) were recorded in the field; and then later analyzed in the laboratory for cation/metals and anion concentrations. Sediment samples were collected along the stream banks, processed, and digested using EPA method 1996 for trace metal analyses and 3050B for mercury analyses. Results showed elevated heavy metal concentrations closer to the city of Jefferson near the confluence of Big Cypress and Black Cypress bayous; heavy metal concentrations decreased as these waters flowed toward the confluence with Little Cypress Bayou and into western Caddo Lake.