Sources of dissolved inorganic nitrogen in a coastal lagoon adjacent to a major metropolitan area, Miami Florida (USA)

Between 2006 and 2007, a study was carried out to determine the relative importance of natural and anthropogenic input of nitrogen into Biscayne Bay (South Florida, USA) using delta C-13 and delta N-15 values of algae, seagrasses, and particulate organic material, delta O-18 and delta N-15 of the NO3- and delta C-13 of the dissolved inorganic carbon. The delta N-15 values of all components showed a strong east to west gradient approaching more positive values (+7 to +10 parts per thousand) close to the land-sea interface. The nitrogen could have emanated from the local waste water treatment plant, septic systems within the region, or nitrogen which had been affected by denitrification and leached from the local landfill, wastewater which had been injected into the Floridan aquifer and leaked back to the surface, and/or some other as yet unidentified source. The measured NO3- delta N-15 and delta O-18 values indicated that the dissolved nitrate originated from anthropogenic sources and was fractionated during assimilation. (c) 2013 Elsevier Ltd. All rights reserved.