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USING MUSSEL ISOTOPE RATIOS TO ASSESS ANTHROPOGEN NITROGEN INPUTS TO COASTAL ECOSYSTEMS
Citation:
McKinney, R A., W G. Nelson, M Charpentier, AND C Wigand. USING MUSSEL ISOTOPE RATIOS TO ASSESS ANTHROPOGEN NITROGEN INPUTS TO COASTAL ECOSYSTEMS. Presented at 6th Annual Meeting of the North Atlantic Chapter of the Society of Environmental Toxicology and Chemistry, Newport, RI, April 14-15, 2000.
Description:
The stable nitrogen isotope ratio in ribbed mussel (Geukensia demissus) tissue was investigated as an indicator of the source of nitrogen inputs to coastal salt marshes. Mussels fed a diet of 15N enriched algae in the laboratory showed an increase in tissue nitrogen isotope ratio ( 15N) over time. Steady-state times were calculated and found to be size dependent, ranging from 206 to 397 days, indicating that mussels are long-term integrators of 15N from their diet and may be reflective of nitrogen inputs to a marsh. Tissue 15N values of indigenous mussels collected from ten salt marshes in Narragansett Bay, RI, showed significant correlations with both the fraction of residential development and the fraction combined agricultural and recreational land use in the marsh watersheds. These correlations suggest that the mussel nitrogen isotope signature is influenced by nitrogen derived from human activities in the adjoining marsh watershed. A more detailed examination of these relationships indicates that land use practices in close proximity to marshes and estuarine characteristics may also influence the observed nitrogen isotope signature. A simple, empirical model based on the ten watersheds was developed to predict mussel 15N from land use characteristics. The predictive ability of the model was tested with data from twelve additional marshes having similar geomorphology as the original ten, but differing in hydrology and mode of nutrient input. The model shows that ribbed mussel nitrogen isotope signatures may provide information on the source of nitrogen to coastal areas that could be of use in developing general policies or strategies regarding monitoring and assessment of coastal eutrophication.