SPATIAL AND TEMPORAL ANALYSES OF WATER QUALITY IN SUBCATHCMENTS OF IRONDEQUOIT CREEK USING GIS

Irondequoit Creek begins in Mendon, NY and flows northward 34 miles emptying into Irondequoit Bay. Irondequoit Bay is a large bay on the southern shore of Lake Ontario and located within the Rochester Embayment Area of Concern (REAOC). Water quality in the REAOC is considered a factor in use impairment. This study investigated major water quality parameters within subcatchments of the Irondequoit Creek watershed in and effort to further delineate the watershed using GIS spatial analyses. Samples were taken at 11 different locations along the creek and its tributaries seasonally during base flow and storm flow events. In-stream measurements were taken using a HydroLab Quanta G for stream pH, total dissolved solids (TDS), dissolved oxygen (DO) and temperature. Flow rate and stream cross section were measured at each location to determine discharge. Laboratory analyses for major elements were completed using ion chromatography (IC) and ICP-AES and alkalinity was determined by titration. Moderately high TDS values ranging from 0.6 to 1.2 g/L at base flow are reflective of the suburban characteristic of the watershed. Spatial analyses of TDS values using GIS show specific reaches of the watershed that contribute higher than average quantities of TDS. A wetland at the northern end of the creek has the tendency to reduce TDS before it enters the bay. Sodium concentrations were found to be widely variable, ranging from 66.0 mg/L to 310.2 mg/L at base flow. This variation may be attributed to the local upwelling of deep groundwater that has intercepted halite deposits. The impact local upwelling is further evidence by a strong correlation between Na and TDS with a correlation coefficient of 0.85. Water quality was also found to vary seasonally and during storm flow events. Dissolved oxygen (DO) was determined to average 12.7 mg/L during April base flow but dropped to an average of 6.8 mg/L during a July storm flow event. All water quality and discharge data is evaluated both spatially and temporally using ArcView GIS. Results of the analyses identify specific reaches of the creek that show a higher degree of use impairment, and quantify loadings to Irondequoit Bay. These results are useful in developing watershed management plans.