DOC AND NUTRIENT EXPORT FROM A SMALL OHIO WATERSHED DURING STORM EVENTS

A study of how storm events affect water quality within the watershed of a small stream, tributary to the Olentangy River, is on-going. The Olentangy River and its tributaries flow through the city of Columbus, Ohio and lie primarily in Devonian Columbus limestone and the overlying glacial till. This first-order stream has a watershed encompassing 4.07 square kilometers and supporting a variety of land uses, including open fields, forest, residential, park land and the Ohio State University’s airport. Samples have been collected biweekly since Spring 2002 and more frequently during storm events. Preliminary data collection and analyses include major ions, nutrients, silica, dissolved organic carbon, suspended solids, pH and titration alkalinity. Event sampling in this first order stream show little change from baseflow concentrations of K, Mg, Ca, and titration alkalinity. The observed constancy of the cation and alkalinity concentrations suggest the primary control of these ions is by the limestone bedrock geology. Dissolved organic carbon increased slightly during storm events from 3 mg carbon/L to 4 mg carbon/L. We hypothesize that the observed DOC increases result from leaching of organic matter stored in soils. Total suspended solids increased from 2 mg/L to 24 mg/L during storms, probably as a result of increased overland flow. Nitrate concentrations have ranged between 1–4 mg/L and average 2.4 mg/L (n=9). Nitrite has been detected only once, at 0.5 mg/L. All orthophosphate concentrations have been less than 0.05 mg/L. In addition to these data, nutrient loadings resulting from storm events will be discussed.