Land Use Impact on Bioavailable Phosphorus in the Bronx River, New York

Abstract

Various forms of phosphorus (P) could become bioavailable such as from desorption, dissolution and enzymatic hy-drolysis. Potential bioavailable P estimation is critical to minimize eutrophication in freshwater systems. Thus, this study was conducted to predict potential bioavailable P in the water columns and sediments and their relations with enzymatic hydrolysis, and estimate impacts of land use and anthropogenic activities on P bioavailability, P transport and water quality in the Bronx River, New York, USA. In sediment samples collected in 2006, total P (TP), total inorganic P (IP), total organic P (OP) and bioavailable P (BAP) were in highest concentrations in sites located at Bronx River Valley upstream in Westchester (site 2), Troublesome Brook (TB, site 4), Sprain Brook (SB, site 7b) and Bronx River estuary near Sound View Park (site 14) respectively. Also, phosphodiesterase and native phosphatases (PDEase and NPase) hydrolyzed distinguishingly high amounts of OP or enzymatically hydrolysable P (EHP) in samples from sites 4, 7b, 10 (New York Botanical Garden) and 14. Microbial P was in negative values (caused by different bacteria and microorganisms could not be paralyzed by chloroform), and the most negative concentrations were appeared at sties 4 and 14. Spatial comparisons among different locations showed distinguished characteristics in tributaries and estuary. In sediments collected in 2007, TP, BAP and IP were in highest concentrations at sites 7-SB, 11-Bronx Zoo, 12-East Tremont Ave Bridge where fresh and saline water meets, 13-estuary facing Hunts Point Waste Water Treatment Plant (HP WWTP) and 14-estuary along Sound View Park. Besides, PDEase-P highest concentrations appeared at sties 7, 13 and 11, NPase-P concentrations were highest at 7 and 11. Microbial P was highest at sties 11 and 14. Spatial variations showed that higher P content and more intense enzymatic hydrolysis in silty clay finer sediments at site 7, 11 and 13. Temporal variations between the two years' data showed land use and other anthropogenic factors' impacts on P transport in river and deposit in sediments. Analysis of the river water samples showed that average soluble reactive P (SRP, 67 µg·l-1) in 2006 and SRP (68µg·l-1) in 2007 both were greater than background P concentration in most natural water (42 µg·l-1). Water TP (TP water) peaks showed at sites 7 and 13 in 2006; TP water were highest at sites 6 and 13 in 2007; showing high P content in water columns at TB and estuary downstream in both years. Similarly, native phosphatases hydrolyzed substantial amounts of OP in the water samples at optimal temperature in both years, indicating potential threats to river water quality as the rise in water temperature may be imminent due to global climate change. Overall, incidental sewer overflows at Yonkers, oil spill at East Tremont Avenue Bridge, urban constructions at Woodlawn Metro-North train station, fertilizer application at WC lawns and gardens, animal manure from the zoo, combined sewer overflows (CSOs), storm water runoff from Bronx River parkway, and potential pollutants from East River all appeared to be influencing spatial and temporal variations on P transport in the river. Research data from this study could be shared among United States Environmental Protection Agency (USEPA), New York City Department of Environmental Protection (NYCDEP), New York State Department of Environmental Conservation (NYSDEC) and Bronx River Alliance to help make effective environmental policies on P application, in turn, improve water quality of the Bronx River and restore its ecology.