FACTORS CONTROLLING WATER QUALITY OF THE ESOPUS CREEK WATERSHED, NEW YORK

The Ashokan Reservoir watershed is one of the main drinking water sources for New York City. Monitoring the temporal changes of water quality parameters upstream and downstream of this reservoir is very important due to the significantly large population that is dependent upon this resource. The aim of this study is to develop a dataset of current water quality parameters and identify factors that control these parameters for comparison to future research. Fifteen sites were selected upstream of the reservoir in the Stony Clove Creek, a tributary of the Esopus Creek, and its tributaries. Seven sites were selected downstream of the reservoir in the lower Esopus Creek. Lab and field parameters including temperature, pH, dissolved oxygen (DO), conductivity, total dissolved solids (TDS), turbidity, alkalinity, and major cation (Sodium, Potassium, Lithium, Ammonium, and Magnesium) and anion (Nitrate, Phosphate, Nitrite, Chloride, Sulfate, Fluoride, and Bromide) concentrations were measured for each site. Ion concentrations were determined using an Ion Chromatograph. Water temperature was found to be higher and the concentration of dissolved oxygen was found to be lower downstream of the reservoir. Alkalinity was found to be higher in the lower Esopus Creek where it flows over Paleozoic carbonate rocks. The upper Esopus basin is generally dominated by silica-rich sandstones with little or no buffering capacity; however one sampling point in the Stony Clove Creek displayed abnormally high alkalinity values due to the installation of imported rip rap of calcareous rock for stream bank stabilization. Nitrate concentrations were found to be significantly higher at sites in the Esopus Creek below the reservoir. Turbidity was found to be higher at sites upstream of the reservoir, especially in the lower Stony Clove Creek and Warner Creek, one of its tributaries. These water quality parameters are most likely controlled by differences in land use practices and heterogeneous glacially-derived surficial geology.