ORGANIC MATTER SOURCES AND TRANSPORT IN THE UPPER SCIOTO RIVER, OHIO

The quality, quantity, and sources of suspended organic matter were studied in the Upper Scioto River in Central Ohio. The Upper Scioto 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. The three sampling locations for the study are in areas whose land use is primarily agricultural and were chosen because of their accessibility and location upstream of the major reservoir on the river. Summer baseflow conditions were compared to Autumn high flow conditions. Variables examined in the suspended matter included the total suspended solids concentration, semi-quantitative concentrations of lignin, carbohydrate concentrations, total organic carbon, total and organic phosphorus, and d¹³C. Also examined were ratios of carbon to nitrogen, organic carbon to organic phosphorus ratios and fluxes of total organic carbon. The primary hypothesis of this research was that the quality (or biodegradability) and quantity of organic matter in the Upper Scioto River would increase during Autumn stormflow conditions due to inputs of fresh terrestrial organic matter. The Autumn suspended matter was also expected to reflect C4 plant contributions from corn organic matter. Results show that the quality and quantity of organic matter were greater during Summer, as reflected in low molar ratios of organic carbon to organic phosphorus, higher carbohydrate concentrations in Summer and higher organic carbon content of the suspended matter in Summer. Summer suspended matter was 20.6% organic carbon and Autumn suspended matter was 11.7% organic carbon. Carbon to nitrogen molar ratios in both seasons were very close to the Redfield ratio (6.6:1 in Summer and 6.7:1 in Autumn). Total suspended matter and total organic carbon concentrations were lower in Autumn (10.3 mg/L TOC and 17.7 mg/L TSS) than in Summer (24.7 mg/L TOC and 39.0 mg/L TSS), but the fluxes were greater in Autumn due to greater stream flow. Stable isotope analyses suggested a phytoplankton or C3 plant source for Summer organic carbon (mean d¹³C of -24.8 o/oo) and a phytoplankton or C4 plant source for Autumn organic matter (d¹³C of -21.5 o/oo).