THE GEOCHEMICAL EVOLUTION OF URBAN WATERS: LESSONS FROM COLUMBUS, OHIO

The hydrological cycle in urban landscapes is complicated by the movement of precipitation through human-made infrastructure, its contact with impervious surfaces and its processing to provide municipal water supply. These processes not only change the flow paths, residence times and overall water balance within the urban environment, but also directly impact the biogeochemical characteristics of the water. We have identified a number of different urban water types from Columbus, OH, the 14^th largest city in the US, and analyzed them for their geochemistry. The Scioto River, a major tributary to the Ohio River, flows through the center of the city, and was the focus of the work. The water types include: urban rain, both aerial and subterranean transported storm runoff, municipal tap water, first order urban stream water, river water entering the city from a rural source, and river water from the metro center. Precipitation is modified as it interacts with impervious surfaces in the urban corridor, and with agriculturally dominated landscapes north of the city. The geochemistry of low order urban tributaries reflect both urban runoff and soil-water interactions. Water treatment greatly modified the rural inflow water. The downtown portion of the Scioto serves as an integration of all the major water types and clearly represents a mix of the rural inflow and urban storm runoff. For example, the rural input waters become more enriched in Na-Cl relative to Ca-HCO₃ and they mix with urban runoff. We discuss the chemical evolution of the waters in terms of future impacts of continued urban/suburban growth and potential climate change.