THE IMPACT OF IMPERMEABLE SURFACE RUNOFF ON THE GEOCHEMISTRY OF THE OLENTANGY RIVER

Runoff from impermeable surfaces, parking lots, and other infrastructure in urban environments can have a profound impact on the geochemistry of natural waters. These inflows can be significant sources of solutes, trace metals, nutrients, and organic compounds, though the flux of water, and dissolved constituents can vary substantially in response to storm events. In this study we measured water geochemistry of the Olentangy River as it flows through the northern portion of The Ohio State University campus, Columbus, OH, as well as from two outfall pipes that funnel urban runoff from nearby parking lots and buildings that discharge directly into the river. We utilized rainfall data and GIS mapping to calculate NO₃^-, PO₄^3-, and Cl^- flux entering the river from the discharge points. Stable isotopes (δ²H, δ¹⁸O) have been analyzed to determine the source and residence time of the storm outflow water. Preliminary results show that isotopic compositions of river and outfall waters fall on the local meteoric water line (LMWL), reflecting recent rainfall. However, the δ²H and δ¹⁸O of the outfall waters show larger variation than the river water, suggesting different residence times and the impact of episodic storm events. TDS values of water samples from the two outfall sites are more variable than the river, and were routinely 2 to 5 fold higher concentrations. Waters from the outfall pipes generally had significantly elevated Na⁺ and Cl^-. In contrast, river water samples tended to have elevated PO₄^3- and NO₃^- concentrations compared to the outfall samples. These higher nutrient values in the river reflect the importance of the agriculturally dominated land use north of the city. Interpretation of the geochemical results is ongoing. These preliminary data demonstrate how impermeable surface runoff chemistry affects natural river water.