Spoon River Nitrate Investigation

It is well established that tile drainage transports nitrate to streams in central Illinois which ultimately flow to the Gulf of Mexico and contributes to the formation of a seasonal hypoxic zone.  The Spoon river watershed is one of central Illinois’ streams that contribute to this environmental problem.  The purpose of the study was to monitor and evaluate the nitrate concentrations within the Spoon River watershed as the river flows downstream.  We collected river samples and analyzed their nitrate concentration in order to better understand N dynamics in the Spoon River watershed.  Within the Spoon River, located in the Upper Salt Fork Watershed, nine samples were collected on June 5, 2012, starting at the origin following downstream to the watershed outlet (designated by the location of a USGS gauging site).  After analyzing the data set from June 5, 2012, results showed a decrease in nitrate concentration from upstream to downstream especially within a 3 miles reach between roads 2700 N and 2400 N.  A follow up of five water samples were taken from the 3 mile reach on June 8, 2012.  The results generally support our hypothesis that nitrate concentrations decreases as the Spoon River flows downstream (10.6 mg L^-1 in the headwater to 5.0 mg L^-1 at the USGS gauge). We speculate that stream nitrate concentrations are decreasing due to the processes of instream denitrification and algal uptake (benthic filamentous green algae).