A HYDROGEOCHEMICAL STUDY OF A WATER RETENTION BASIN, ODELL’S POND

This study initiated a baseline hydrogeochemical survey of Odell’s Pond, a manmade water retention basin (85,000 m³, 900,000 m²) on the campus of Hobart and William Smith Colleges in Geneva, NY. Samples were collected each week from January through July of 2004 at the outflow of the pond along with five precipitation event samples from the pond site and the only stream that empties into the pond from May through July. Each sample was filtered at 0.45 um under vacuum and analyzed for dissolved nutrients (phosphate, nitrate and silica), conductivity, major ions (F, Cl, NO₃, SO₄, Na, K, Ca, Mg), alkalinity, total suspended solids, pH and dissolved oxygen. A detailed bathymetric map was also created using GPS and GIS technologies. The concentration of all the measured parameters decreased by one or two orders of magnitude from winter to summer, except for phosphate, dissolved oxygen, pH, temperature and fluoride which increased by a similar magnitude. Regardless, the input stream concentrations in summer were closer to the summer pond concentrations. For example, phosphate concentrations increased from 0.3 ug/L to 22 ug/L in the pond with summer concentrations of 20 ug/L to 32 ug/L for the stream. Sodium concentrations decreased from 600 mg/L to 46 mg/L in the pond with summer concentrations of 15 mg/L to 96 mg/L in the stream. The conductivity data directly correlates to the major ion concentrations, especially sodium and chloride (r² values of 0.96 and 0.99). These temporal trends and covariance suggests that salt-rich surface runoff of road salt in the winter was diluted by changing stream chemistry over time through snow melt and precipitation event runoff, and/or nearby watering of athletic fields and perhaps groundwater influx. Nitrogen is the limiting nutrient in the pond and is probably quickly assimilated by the macrophytes surrounding the perimeter of the pond. Future work will incorporate a detailed hydrogeochemical model to assess the relative contribution of each hypothesized source.