MAJOR ION AND NUTRIENT SOURCES IN THE SCIOTO RIVER, OHIO

Rapidly growing and urbanizing Columbus, Ohio, is the 14^thlargest city in the United States. The city is located at the confluence of the Scioto River with one of its largest tributaries, the Olentangy River. The Scioto River watershed lies in the Eastern Cornbelt Plains and encompasses 1860 km² in the predominantly agricultural Wisconsin glacial till plains covering west-central Ohio. The watershed is underlain by Silurian and Devonian limestone and dolostone bedrock. Water quality in the Scioto River and its four major tributaries reflect the agricultural landuses of its upper reaches, the carbonate bedrock and its overlying till, and the urban and suburban inputs from the city population of 922,000 inhabitants in 2020. Nearly synoptic sampling conducted in the course of several campaigns during the summers of 2019 and 2020 shows the strong influence of bedrock geology and agricultural inputs on the headwater aquatic chemistry. Phosphate and nitrite+nitrate concentrations are highest in the agricultural areas north and south of Columbus and are approximately triple those in the urban portions of the river. Sodium, chloride, and sulfate all increase downstream of the urban core, probably due to inputs from road salt and sewage outflows. The southerly locations sampled are also likely influenced by high agricultural inputs and possibly sewage from diffuse sources and treated discharge from small treatment plants. The results demonstrate multiple sources of solutes to the Scioto River, both urban and agricultural, and how changing landuse affects water quality along the length of the river.