A SEDIMENT RECORD OF STRIP MINING AND AMD DISCHARGE AT LAKE HARRIS, TUSCALOOSA COUNTY, AL

Lake Harris, a man-made reservoir constructed in 1929, is a source of water for industry and the tertiary source of domestic drinking water for Tuscaloosa County, Alabama. Coal-rich deposits hosted by the Pottsville Sandstone in the Black Warrior Basin attracted the coal mining industry to the drainage basin during the 1970s. Shallow coal seams were removed by strip mining, which produced increased sedimentation and acid mine drainage (AMD). A first-order stream feeding the lake still shows the effects of AMD three decades after remediation, although the lake water is un-impacted. This study examines a lake sediment core to determine if the impact of strip mining and AMD are preserved in the sediment record. An 84cm long sediment core was collected from a location within the lake which is presumed to consist of undisturbed sediment strata. ²¹⁰Pb (t_1/2=21 years) dating and the constant rate of supply (CRS) approach were used to calculate rates of sediment deposition over the last 86 years. The ²¹⁰Pb sediment dating method was chosen for this study because of its accuracy in dating the most recent one hundred years of sedimentation. The sediment core was sectioned into 33 2.5-cm intervals and the pore water was extracted from each section and analyzed by ICP-OES for cation concentrations. HPGe gamma spectroscopy will be used to analyze for excess ²¹⁰Pb to feed the CRS model. Correlation of sedimentation rates with pore water cation concentration data will be performed to determine the relationship between metal fluxes and the age date of their deposition. Ultimately, this dataset will be compared with data being collected from the severely AMD-impacted stream to determine the potential impacts of continued AMD discharge on lake water quality and the food web.