GEOCHEMISTRY OF URBAN KARST WATERS AND ITS INFLUENCE ON AN URBAN RIVER

The intricate network of subsurface pipes in urban environments have similar hydrological attributes to karst environments, so similar in fact that this system of underground pipes has been termed “urban karst”. These pipe networks transfer municipal water, domestic sewage, and storm runoff from impervious surfaces, such as roadways, sidewalks, buildings and other built infrastructure. Subsurface water can be lost in the subsurface from leaky pipes and transported to local streams and rivers, especially during precipitation events This water, in turn, can affect the chemical composition of these receiving waters. We have investigated a ~ 5.5 km transect along the Olentangy River from the town of Worthington, Ohio to the center of the Ohio State University campus, in Columbus, OH. Over this distance we estimate 13 urban karst outflows delivering water from eastern portion of the urbanized catchment discharge directly into the river. We have analyzed both the outfall and river waters for major ions, nutrients, and stable isotopes of water for ~12 month period at 2 outfall locations; plus we have shorter frequency data sets from other sites along the river transect. Our data suggest that these urban karst sources deliver waters with higher concentrations of some dissolved constituents, such as Cl (146 to >13000 µM), H₄SiO₄ (15 to >213 µM), and K (16 to >230 µM), to the river waters. The river nutrient sources, especially NO₃ (<1 to 384 µM), are dominated by agricultural active areas upstream of the urban regions of the watershed. The stable water isotope data indicate that a portion of the urban karst waters have either longer residence times in the subsurface, or different sources than the local, daily event precipitation. Given estimated recharge in the karst catchments, we will present fluxes of Cl, and other solutes into the river.