Phosphorus Transport in the Bronx River: Qualitative and Quantitative Analysis

Phosphorus (P) is the primary limiting nutrient for algal growth in freshwater systems. Excessive P from external inputs and release from sediments could accelerate primary productivity leading to eutrophication in the water column, and consequently degrading water quality. The objectives of this study were to predict P bioavailability and estimate spatial and temporal variations in P transport in the Bronx River, New York, USA. The Bronx River originates from the Westchester Davis Brook and Kensico Dam, flowing south through Westchester County (WC) and Bronx to the estuary area where it joins the East River. The total length is about 20 miles. There are more than 100 stormwater and other discharges that flow to the river along the entire length from Westchester to the East River. The upper part of the river is freshwater, while the lower is saline. The overall goal of this research is to provide data that can help develop policies to control P runoff to the river, including regulation of P inputs from lawn fertilizers. It is hoped this data can be shared meaningfully among the United States Environmental Protection Agency (USEPA), Department of Environmental Protection (DEP), Department of Environmental Conservation (DEC), Bronx River Alliance to make the river meet the fishable/swimmable goal of the Clean Water Act. The 31P-NMR spectra showed that the dominant P species in Bronx River bed sediments were orthophosphate monoester, and lesser phosphate diesters and pyrophosphates (pyro-P). The P compounds were mostly glycerophosphate (GlyP), nucleoside monophosphates (NMP), and polynucleotides (PolyN). A few sites showed a small amount of dihydroxyacetone phosphate (DHAP), inosine monophosphate (IMP), and pyrophosphates (pyro-P). The P sorption capacity of the bed sediments of the Bronx River was very high, and the maximum values of P sorption maximum (Smax) was 476 mg kg-1, equilibrium P concentration (EPC0) was 0.73 mg L-1, and originally sorbed P (S0) was 65.6 mg kg-1. Sediments could potentially release P into the water column as the soluble reactive P (SRP) in the water column drops below EPC0 under changing hydro-climatic conditions such as the changes in pH, redox etc. Correlation analysis showed that Smax was correlated with poorly crystalline and amorphous Fe, Al, acid-extractable Ca and Mg, and organic matter suggesting their influence on P sorption capacity of the sediments. Similarly, the bed sediments contained various P pools, and rank order was: HCl-P \u3e NaOH-P \u3e NaHCO3-P \u3e residueP, and the relative proportion of 3.7: 2.0: 1.4: 1 in 2006 sediment; HCl-P \u3e NaOH-P \u3e residue-P \u3e NaHCO3-P, with their relative proportion of 27.8: 6.2: 2.7: 1 in sediment collected in 2007. The sediments P mineralization studies that were conducted under flooding conditions for 0, 7, 15, 30 d showed changes in the size of the P pools, indicating variations in microbial activities during incubation period. Moreover, enzyme incubation studies showed that phosphodiesterase (PDEase) hydrolyzed up to 82% of OP. Native phosphatases (NPase) hydrolyzed substantial amount of OP (up to 76%) when incubated at 37ºC, indicating that OP could be hydrolyzed under favorable temperature, and there is a potential threat to river ecosystems if global rise in temperature continues. Water samples from the river showed that the SRP concentrations were higher than EPA standard of 15 μg L-1 (SRPmax=221 μg L-1, SRPave=68 μg L-1), and TP concentrations were in a substantial amount (TPmax=1,113 μg L-1, TPave=438 μg L-1) compared with other rivers such as the Garonne River in southern France. The hydrolyzed OP by NPase was up to 100% when incubated at 37ºC indicating potential threat to water quality under changing hydro-climatic conditions. It is indicative that anthropogenic inputs such as the P fertilizer runoff from garden and golf course, sewer overflows from Hunts Point WWTP, raw sewer discharge along the river (e.g., from Yonkers), CSOs, land use changes, as well as hydro-climatic changes may cause the spatial and temporal variations on P transport in the Bronx River