Collaborative Research: Role of Atmospheric Nitrogen Deposition in Estuarine and Coastal Production and Food Chain Dynamics

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Atmospheric deposition, as rainfall and dryfall, is an increasingly important source of biologically-utilizable nitrogen in estuarine and coastal regions: about 30% of their combined nitrogen loading comes from atmospheric sources. Nitrogen from atmospheric deposition may be a unique source of nitrogen in coastal waters, as direct surface water deposition may occur downstream of estuarine nutrient stripping zones that assimilate the majority of terrigenous nitrogen loading. Moreover, analyses of rainwater reveals that dissolved organic matter can be a significant fraction of the total dissolved nitrogen in precipitation from both continental and oceanic origins. This nitrogen from rainfall has been shown to stimulate primary production in coastal waters adjacent to North Carolina. Impacts of atmospheric nitrogen deposition will be elucidated by assessing algal primary production and trophic responses with complementary bioassays and stable isotope tracers measurements at the natural abundance level. The three sources of nitrogen in rainwater (nitrate, ammonium, and dissolved organic nitrogen) will be followed into primary producers with stable isotopes, while species composition and photosynthetic rates are monitored. The transfer of primary products from algae to both microbial and zooplankton populations will be assayed to investigate the response of grazing and the microbial loop to increased productivity. A quantitative model and budget of nitrogen entering the area from atmospheric deposition will be the final result of the study. Results may be useful to global modelers attempting to assess the importance of atmospheric deposition on climate and species diversity.