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Carbon Stable Isotopes as Indicators of Coastal Eutrophication
Citation:
Oczkowski, A., E. Markham, Alana Hanson, AND C. Wigand. Carbon Stable Isotopes as Indicators of Coastal Eutrophication. ECOLOGICAL APPLICATIONS. Ecological Society of America, Ithaca, NY, 24(3):457-466, (2014).
Impact/Purpose:
One of the major themes (if not the major theme) of coastal ecology research today is to understand how human sources of nutrients impact coastal ecosystems. Despite the prevalence of this issue, scientists and managers remain challenged with how to efficiently monitor and assess the role of anthropogenic nutrients in estuarine eutrophication. We present data to support the idea that carbon isotopes may be an excellent tool to monitor ecosystem production and,when used in conjuntion with other indicators, a cost-efficient and time-efficient metric for identifying and monitoring ecosystem productivity.
Description:
Coastal ecologists and managers have frequently used nitrogen stable isotopes (δ15N) to trace and monitor anthropogenic nitrogen (N) in coastal ecosystems. However, the interpretation of δ15N data can often be challenging, if not confounding, as the isotope values fractionate substantially during uptake and release by biota. In contrast, carbon isotopes (δ13C) fractionate little on uptake, and there is a growing body of evidence that demonstrates their utility as indicators of eutrophication. While they don’t monitor the nutrients directly, they may provide evidence of the associated enhanced primary production. We provide three examples of systems where δ13C values sensitively track phytoplankton production. First, earlier (1980s) mesocosm work establishes close positive relationships between δ13C and dissolved inorganic nitrogen and dissolved silica concentrations. Consistent with these findings, a contemporary mesocosm experiment designed to replicate a temperate intertidal salt marsh environment also demonstrated that the system receiving supplementary nutrient additions had higher nutrient concentrations, higher chlorophyll concentrations, and higher δ13C values. This trend was particularly pronounced during the growing season, with differences less evident during senescence. And finally, these results were replicated in the open waters of Narragansett Bay, Rhode Island during a spring phytoplankton bloom. These three examples, taken together with the pre-existing body of literature, suggest that, at least in autotrophic, phytoplankton dominated systems, δ13C values can be a useful and sensitive indicator of eutrophication.
