EFFECT OF INCREASING ALKALINITY AND PH IN THE DISTRIBUTION COEFFICIENTS OF HEAVY METALS BETWEEN SEDIMENTS AND PORE WATER IN A LAKE AFFECTED BY ACID MINE DRAINAGE

Lake Hope in Vinton County, Ohio, is a man-made lake affected by acid mine drainage (AMD) from coal mines located in its watershed. The chemistry of sediments, pore water, and lake water were investigated. The contaminated AMD water entering the lake improves as the water moves towards the dam that formed the lake. Alkalinity titrations along the lake show that the rise in pH is likely to be produced by the input of alkaline groundwater. Water quality improves as you approach the dam. In comparison, the sediments show lower concentration of heavy metals close to the AMD discharging point and higher concentrations in the deeper region, close to the dam. Sequential extraction of metals in the sediments show that the highest fractions correspond to the oxidized iron and manganese hydroxides and the detrital fraction or eroded fragments from the watershed. Distribution coefficients for the heavy metals between the sediments and pore water show two different trends along the lake. For Al, Fe, Co, and Ni the distribution coefficient decreases within one order of magnitud along the length of the lake. For other cations such as Pb, Cr, Zn, Cu and Mn, the distribution coefficient shows a more stable trend with small variations due probably to the input of sediments from the watershed. These results show that the increased concentrations in heavy metals in the sediments also increases the concentration in the pore water and that the distribution coefficient for Al, Fe, Co, and Ni decreases with increasing alkalinity and pH.