STABLE WATER ISOTOPES OF THE SCIOTO RIVER: SEASONAL AND SPATIAL VARIATIONS OF AN URBAN SYSTEM

The increased intensity and expansion of human development can disrupt natural freshwater systems, particularly in densely populated areas. Such growth poses a challenge for society where the water systems upon which humans rely on for domestic and industrial water are also the most physically and chemically disturbed. Stable water isotopes (δ¹⁸O and δ²H) serve as natural tracers to study hydrologic patterns of rivers as they flow through urban landscapes. In this work, we investigate the seasonal and spatial hydrologic patterns of the Scioto River in Columbus, Ohio, the 14^th largest city in the USA, by analyzing river stable water isotopic composition. Over the year of 2021, we sampled five locations along the Scioto River as it flows from an intense agriculture landscape through two major reservoirs and the city of Columbus, Ohio. Scioto River δ¹⁸O and δ²H values ranged from -12.32‰ to -4.86‰ and -82.2‰ to -28.7‰. River isotopic patterns reflected a dampened seasonal precipitation pattern, with water enriched in heavier isotopes in warm months and depleted of heavier isotopes in cool months. There was greater variability in the δ¹⁸O and δ²H values in the upstream, agricultural reaches of the Scioto River, which was likely due to the influence of agricultural tile drain runoff and lower volume of water in the headwaters and upstream reaches of the river. As the Scioto River travels through the metropolitan area of Columbus, tributaries join the mainstem and the river flows through two river-like reservoirs that supply drinking water to the Columbus metropolitan area. These river-lacustrine systems generated isotopic homogenization along the Scioto without causing isotopic enrichment that is commonly observed due to evaporation in river-reservoir systems. This study underlines the effects of urbanization and intensive agriculture on rivers. As climate change induces shifts in the hydrologic cycle, this work also emphasizes the importance of studying urban river hydrology in the context of both climate change and human influence.