INVESTIGATION OF NITRATE CONCENTRATIONS WITHIN THE MIDDLEFORK RESERVOIR WATERSHED, WAYNE COUNTY, INDIANA

Middlefork Reservoir (MR), a Public Community Water Supply (PCWS) source in Richmond, Indiana, commonly undergoes eutrophication during the summer. Eutrophication is partly due to excess nitrate introduced to the reservoir. The purposes of this study were to: 1.) quantify nitrate concentrations in tributary drainages within the MR watershed, 2.) observe changes in concentrations at sampling locations over time and 3.) interpret spatial and temporal nitrate concentration patterns by use of a Geographic Information System (GIS).

Forty sampling locations were selected at intersections of perennial streams and county roads. Samples were collected in clean 125 ml HDPE bottles, (rinsed 3 times with the sample) and then refrigerated. Samples were collected every 5-9 days from 3/26/2002 to 4/26/2002. Rainwater was collected over this same interval. Conductivity, pH, and temperature measurements were acquired by use of a WTW P4 Multimeter; field parameters were entered into a Trimble GeoExplorer III Global Positioning System (GPS) unit. In the lab, GPS data were subjected to differential correction and then downloaded (with field parameters) directly into ArcGIS 8.2.

Nitrate concentrations were measured in water samples (warmed to room temperature) and analyzed on a Oakton Ion 510 with a Cole-Parmer 27502-31 Nitrate Electrode. Sample analyses were conducted according to Standard Method 4500-NO3- D which included adding a buffer solution to all samples for removal of non-nitrate ion interferences.

Analyses results ranged from 0.35 ppm to 6.52 ppm; these results correlated with land use. 62% of samples exceeded the background value of 2 parts per million (ppm) indicating human influence. Locations exhibiting low nitrate concentrations (sites 3, 21 and 19) have forest cover and are located in the upper reaches of the watershed. Locations with elevated nitrate concentrations (sites 40, 34 and 36) are characterized by tile drainage systems and concentrated livestock populations. Nitrate at these locations indicate significant anthropogenic additions to the MR watershed. Spatially, nitrate concentrations were observed to decrease with flow distance suggesting dilution effects. Temporally, nitrate concentrations fluctuated only slightly at each location.