FROM CORNFIELDS TO SKYSCRAPERS: ISOTOPIC COMPOSITION OF CENTRAL OHIO RIVERS

Stable water isotopes δ¹⁸O and δD are widely used as conservative tracers to determine hydrologic cycling in surface water systems. Previous work has shown that river water δ¹⁸O and δD signatures are reflections of local precipitation that may be influenced by weather conditions and residence time. In this work we investigated isotopic composition of the Scioto River and its main tributaries in central Ohio to discern hydrologic cycling processes throughout these agricultural and urban systems. Columbus, Ohio, with its 2020 population of 922,000 people, is the 14^th largest city in the United States. Unlike many of its Midwestern urban neighbors with similar or smaller population density, such as Chicago and Detroit, Columbus is rapidly growing, and experienced a 16.6% increase in population from 2010 to 2020. For our study, samples were collected in July 2019 and June 2020 along the Scioto River mainstem and from six tributaries. The Scioto originates in an agricultural landscape and travels south through Columbus until it joins with the Ohio River in southern Ohio. Three of the tributary systems sampled include major reservoirs that supply drinking water for the Columbus metropolitan area and recreation for the citizens. River samples fell along the 2012–2020 central Ohio local meteoric water line, and the δ¹⁸O and δD signatures fell within the range of the June and July precipitation isotopic composition. However, river water δ¹⁸O and δD signatures were lighter than their long-term averages for June and July. Lighter river isotopic composition indicated mixing or elongated residence time within the river and reservoir system and little evaporative effect. Nonetheless, we observed a degree of evaporation throughout the downstream transect sampled in 2019. Results provide insight into water cycling processes within the Scioto River system as it traverses the agricultural to urban landscape of central Ohio. No strong evaporative effect of water within the Scioto system influenced water resources during summers of 2019 and 2020.