FINGERPRINTING OF WATER SOURCES TO OTTER CREEK IN CORTLAND COUNTY, NEW YORK, USING IN SITU MEASUREMENTS

Otter Creek is a small, intermittent stream located within Cortland County in central New York. Water sources to the channel include groundwater from a glacial aquifer, surface water from the headwaters and precipitation, and road runoff via storm drains. Using a multi-parameter water quality probe, four water quality parameters were measured in order to characterize these water sources and to distinguish their influence on lower Otter Creek. The four parameters measured were pH, dissolved oxygen (DO), specific conductance (SC), and temperature. Measurements were taken at six surface water locations along Otter Creek and in groundwater from the Cortland Water Works on a weekly basis from March to April, 2012, and before and during a rain event in October. Discharge was measured at four locations through the spring using a flow meter.

Surface water in the upstream study reach had relatively constant pH, DO and SC in the spring (means and standard deviations of respectively 8.1 ± 0.1, 11.8 ± 0.5 mg/L, and 623 ± 22 μS/cm), while temperature was more variable and generally reflected air temperature. Groundwater also had relatively constant characteristics (pH = 7.7 ± 0.1, DO = 6.6 ± 0.4 mg/L and SC = 645 ± 11 μS/cm) plus a more stable temperature of ~10°C. Outflow from a duck pond at the Cortland Water Works added additional water to lower Otter Creek during the spring and had pH = 7.7 ± 0.1, DO = 10.4 ± 1.0 mg/L, SC = 774 ± 17 μS/cm, and temperature near 9.8°C. Full mixing of the duck pond outflow with lower Otter Creek did not occur until a bend 200 meters downstream of the confluence. During the fall, a storm drain was discovered that added water with high specific conductivity (1100 μS/cm) 15 m from the confluence.

The water characteristics of lower Otter Creek in spring 2012 suggest that it was a combination of precipitation runoff from the headwaters, water from road drains, groundwater, and outflow from the duck pond. These latter two sources became increasingly important in April, and this is supported by the discharge measurements. The duck pond itself appears to be fed by groundwater, but perhaps from a different depth to the groundwater tapped by the city wells. The high specific conductivity of water from the storm drain and duck pond may reflect road salting on the adjacent streets.