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Trends in nitrogen isotope ratios of juvenile winter flounder reflect changing nitrogen inputs to Rhode Island, USA estuarine systems
Citation:
Pruell, R., B. Taplin, AND K. Miller. Trends in nitrogen isotope ratios of juvenile winter flounder reflect changing nitrogen inputs to Rhode Island, USA estuarine systems. MARINE POLLUTION BULLETIN. Elsevier Science Ltd, New York, NY, 118(1):41-47, (2017).
Impact/Purpose:
This manuscript advances the development of methodology to assess the influence of anthropogenic nitrogen in estuarine systems. Juvenile winter flounder were collected from several estuarine systems along the coast of Rhode Island over two three-year periods and nitrogen isotopes were measured in the muscle tissues of the flounder. Nitrogen isotope ratios can be used to indicate the relative importance of anthropogenic versus natural nitrogen sources to a waterbody. The results showed that there was a good correspondence between nitrogen isotope ratios and population density in the watershed of the different waterbodies for all six sampling years. The study also showed that nitrogen isotope ratios can be influenced by biogeochemical processes which must be considered when interpreting these ratios in biota. This information is important to the Agency because it furthers the development of a technique that could be used to monitor nutrient inputs to aquatic systems.
Description:
Nitrogen isotope ratios (d 15N) in juvenile winter flounder, Pseudopleuronectes americanus, were used to examine changes in nitrogen inputs to several Rhode Island, USA estuarine systems. Fish were collected over two three-year periods with a ten-year interval between sampling periods (2002-2004 and 2012-2014). During that interval numerous changes to nutrient management practices were initiated in the watersheds of these estuarine systems including the upgrade of several major wastewater treatment facilities that discharge to Narragansett Bay, which significantly reduced nitrogen inputs. Following these reductions, the d 15N values of flounder in several of the systems decreased as expected; however, isotope ratios in fish from upper Narragansett Bay significantly increased. We believe that low d 15N values measured in 2002-2004 were related to concentration-dependant fractionation at this location. Increased d 15N values measured between 2012 and 2014 may indicate reduced fractionation or that changes in wastewater treatment processes altered the nitrogen isotopic ratios of the effluents.
