Inorganic nitrogen pollution in urban streams of a medium-sized city in upstate New York
Urban areas experience a high volume of chemical and pollutant inputs including inorganic nitrogen (N), but a reduction of biological uptake and retention due to land-use and geomorphology alterations. Runoff in cities can pollute streams and rivers, degrade water resources and contribute to eutrophication. We conducted a study in and around Binghamton, a medium-sized city in upstate New York, to evaluate the inorganic N contribution to the Susquehanna River from small headwater streams draining urban watersheds and from the area wastewater treatment plant (WWTP). From June 2011-May 2013, water samples were collected and discharge measurements were taken from eight streams at locations both upstream and downstream of urban land use and from the WWTP effluent. Immediately before and during the sampling period the WWTP experienced two major incidents that continue to impede its performance today: a wall collapse in May 2011 impaired the plant’s nitrification and denitrification function, and in September 2011 the plant was seriously damaged by flooding from Tropical Storm Lee. Water samples were analyzed for ammonium (NH4+) and nitrate (NO3-) concentrations, pH and conductivity. Land-uses of the eight watersheds were analyzed to explore the relationship between land use and the water chemistry of corresponding streams.
Nitrate dominated stream inorganic N (>95%). Urban development in watersheds ranged from 4.34 to 46.24%. Flow-weighted seasonal NO3-N were generally higher downstream of development compared to upstream, ranging from 0.0-0.43 mg/L upstream and 0.03-0.58 mg/L downstream. NO3-N was significantly higher downstream than upstream in the four most developed watersheds (p<0.01). NO3-N was higher in more developed watersheds, with the strongest correlations between N concentration and development found in summer 2011 (r2=0.71) and summer 2012 (r2=0.57). WWTP effluent was dominated by ammonium (>95%). NH4-N ranged from 2.16-11.78 mg/L and NO3-N ranged from 0.10-2.67 mg/L in the summer of 2011, after the wall collapse. After the flood, NH4-N ranged from 2.45-23.02 mg/L and NO3-N from 0.02-1.15 mg/L. Flow-weighted conductivity and pH ranged from 76-359 µs/cm and 7.02-7.99 upstream, 81-570 µs/cm and 7.51-8.02 downstream, and 864-1675 µs/cm and 7.15-7.91 in effluent, respectively. In 2011-12 and 2012-13 approximately 264 and 411 metric tons of inorganic N from the WWTP and 38 and 60 tons from eight streams were discharged to the river, respectively. Both direct and indirect human impacts on N flows, and natural and human-caused events, negatively affect streams and rivers flowing through the city.