DETECTING SOURCES OF EUTROPHICATION IN COASTAL NORTH CAROLINA USING δ15N VALUES OF SEA GRASSES AND ALGAE

Coastal regions have been known to experience nitrogen pollution in the form of waste-water inputs or agricultural fertilizer runoff that is impacting aquatic biogeochemistry. Excess nutrients lead to eutrophication and cause a multitude of imbalances in coastal waters, including dysoxia. Here we develop an algae and seagrass isoscape in waters within the Cape Lookout National Seashore in North Carolina, from Jarrett Bay and adjoining creeks to the Atlantic Ocean. An approach for detecting impacts of sewage and agricultural sourced nitrogen is the use of stable nitrogen isotopes (δ¹⁵N) in marine plants and algae, which can be bioindicators of aquatic ecosystems. Marine algae are excellent recorders of N inputs because they use N directly from the dissolved inorganic N pool with little fractionation, which is time-averaged over the growing season. Wastewater is typically enriched in ¹⁵N, while inorganic fertilizer is depleted in ¹⁵N. We therefore expect the results to show increased δ¹⁵N values in areas adjacent to densely populated locations (indicating septic tank seepage into the coastal waters), and low δ¹⁵N values in locations receiving agricultural run-off. We hope to pinpoint sources of N to the coastal zone, which could aid various stakeholders such as mollusk aquaculturists. Across the globe we are witnessing rapid environmental degradation as a result of increased nitrogen loading and more generally system instability. With a growing global population, humans are harming the environment at alarming rates, especially along coastlines.