THE INFLUENCE OF AGRICULTURE AND URBANIZATION ON TRACE METAL GEOCHEMISTRY OF THE SCIOTO RIVER, OHIO

Land use change, urban development, and dam construction for flood control and potable water storage significantly alter water chemistry and geochemical cycling. The upper Scioto River watershed in central Ohio is dominated by intensive agriculture near the headwaters and urban/suburban growth downstream at Columbus. The river was dammed for reservoir development in two places in the early 1900s. To investigate the effects of these changes on trace element chemistry, the Scioto River was sampled weekly from late February to early August, then monthly from August to December. Additional samples were collected after precipitation events. Samples were collected from three locations: 1) in primarily agricultural land at the north end of the upstream reservoir, 2) in a suburb of Columbus in the downstream reservoir, and 3) in downtown Columbus. Samples were filtered and analyzed for major ions, nutrients, and trace elements (U, Ni, Cu, Rb, Mo, Ba, Sr). U, Ba, and Sr have moderate to strong positive relationships with Ca and moderate to strong negative relationships with discharge at all three locations, suggesting a geogenic source, as much of the Scioto River watershed is underlain by carbonate bedrock. U, Ni, Mo, Ba, and Sr have moderate to strong negative correlations with NO_x at the agricultural location, but correlations weaken downstream. Generally, linear correlations between trace elements and major ions/nutrients are strongest (>0.75) at the agricultural location, with moderate correlations (+-0.5-0.75) at the suburban location. The urban location had the fewest statistically significant (p<0.05) correlations between trace elements and major ions/nutrients. Longer residence times and altered hydrologic flow regimes due to the reservoirs and local urban inputs could dampen the relationships between analytes observed upstream. Our initial interpretations suggest that both geogenic and anthropogenic sources influence trace element concentrations in the river system. These sources need to be better quantified, especially as the city expands and municipal water demand increases.