Roughly eight million people live on Long Island, including Brooklyn and Queens, and despite improvements in wastewater treatment, nearly all its coastal waterbodies are impaired by excessive nitrogen. We used nutrient stoichiometry and stable isotope ratios in estuarine biota and soils to identify water pollution hot spots and compare among potential indicators. We found strong gradients in δ(15)N values, which were correlated with watershed land cover, population density, and wastewater discharges. Weaker correlations were found for δ(13)C values and nutrient stoichiometric ratios. Structural equation modeling identified contrasts between western Long Island, where δ(15)N values depended on watershed population density, and eastern Long Island where δ(15)N values reflected agriculture and sewage discharges. These results illustrate the use of stable isotopes as water quality indicators, and establish a baseline against which the efficacy of strategies to reduce nutrients can be measured.
