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Carbon and nitrogen isotope ratios of juvenile winter flounder as indicators of inputs to estuarine systems
Citation:
Pruell, R. AND B. Taplin. Carbon and nitrogen isotope ratios of juvenile winter flounder as indicators of inputs to estuarine systems. MARINE POLLUTION BULLETIN. Elsevier Science Ltd, New York, NY, 101(2):624-631, (2015).
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 a period of three years. Stable carbon and nitrogen isotopes were measured in the muscle tissues of the flounder. The results showed that there was a good correspondence between nitrogen isotope ratios and population density in the watershed of the different waterbodies. The study also showed that carbon and 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:
Stable carbon and nitrogen isotope ratios were measured in the muscle tissues of young-of-the-year (YOY) winter flounder, Pseudopleuronectes americanus, collected from several estuarine systems along the coast of Rhode Island, USA. These systems included three coastal lagoons (Ninigret Pond, Green Hill Pond and Point Judith Pond), an estuarine river (Narrow River) and Narragansett Bay. Results from sampling over a three-year period showed some year-to-year variability for 13C within waterbodies; however, 15N values were not significantly different (P > 0.05) within systems among the three years studied. he 13C trends observed along transects in Narrow River and Narragansett Bay showed isotopically depleted terrestrial signals in the upper reaches of the estuaries and more positive values indicative of marine organic material in the lower regions of these systems. Significant differences (P < 0.05) in 15N were observed among estuarine systems. Fish from the coastal lagoons had the lowest 15N values followed by those from Narrow River and then Narragansett Bay. Some unexpected trends in 15N were observed within Narragansett Bay. The Bay has a strong north-south gradient in nutrient concentrations due to large sewage inputs in the upper Bay which was not reflected in flounder 15N values. As expected, YOY flounder from stations in the lower-Bay had depleted 15N values compared to those from the other locations. However, the 15N ratios of fish from stations in mid- and upper-Narragansett Bay were not statistically different (P > 0.05) from each other except for the most northerly station (PCM), which was consistently lower. Depleted 15N values at this nutrient rich station may indicate that factors such as concentration dependant fractionation may need to be considered when using nitrogen isotope ratios in biota to infer the relative influence of anthropogenic nitrogen inputs to coastal waterbodies.
