TEMPORAL AND SPATIAL VARIATIONS IN STREAM WATER CHEMISTRY IN A WATERSHED IMPACTED BY ACID MINE DRAINAGE

Through the damming of Yellow Creek in 1929, Lake Harris, a 220-acre reservoir, was constructed as a secondary source of drinking water for the city of Tuscaloosa. Following the creation of Lake Tuscaloosa in 1970, Lake Harris became the primary source of water for industry and the tertiary source for drinking water. Between 1969 and 1976, shallow coal seams hosted by the Pottsville Sandstone in the Black Warrior Basin, were removed by strip mining and the site was abandoned without reclamation. During the subsequent decade of exposure, until reclamation in 1986, increased sedimentation rates and acid mine drainage (AMD) damaged the aquatic ecosystem of a first-order stream discharging into the lake. Thirty years after reclamation, Lake Harris Stream still shows the effects of AMD. This research examines temporal and spatial variations in stream water chemistry related to the AMD impacts.

Aqueous samples were collected monthly, November ‘15 to October ‘16, from Lake Harris Stream and a control stream located in an adjacent watershed. The samples were analyzed for cation and anion concentrations by ICP-OES and IC, respectively. Temperature, pH, and conductivity were measured in the field and laboratory alkalinity/acidity titrations were completed within 48 hours. The control stream’s water chemistry remained consistent throughout the year, with pH in the 6-7 range. Although Lake Harris Stream water pH values averaged 6-7 December thru February, values ranged between 3-6 during the remainder of the year. Acidic stream water conditions resulted in elevated levels of sulfate, chloride, Al, Ba, Ca, Co, Cr, Fe, K, Mg, Mn, Ni and Sr. Temporally, Fe concentration decreased as pH decreased, whereas sulfate, Al, Co, Cr, K, Mg, Mn and Sr concentrations increased. Spatially, for a given month, sulfate, Ca, Co, Cr, Fe, Mg, Mn, Ni, Na and Sr concentrations correlated positively with one another, increasing as pH decreased, while chloride, Al and Zn concentrations remained constant. PHREEQC modeling indicates a temporal mineral saturation index trend within upstream sites, where water is more highly supersaturated with respect to clays and Fe, Al, Mg, Mn oxides in the winter months. In addition, the lake and stream mouth samples show little change throughout the year, remaining supersaturated with respect to clays and metal oxides.