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

大气沉降，如降雨和干旱，是河口和沿海地区生物可利用氮的一个日益重要的来源：约30%的总氮负荷来自大气来源。大气沉积的氮可能是沿海水域氮的独特来源，因为直接的地表水沉积可能发生在河口营养剥离带的下游，吸收了大部分陆源氮负荷。此外，对雨水的分析表明，溶解有机质可能是大陆和海洋降水中总溶解氮的重要组成部分。来自降雨的氮已被证明可以刺激北卡罗莱纳州附近沿海水域的初级生产。大气氮沉降的影响将通过补充生物测定和稳定同位素示踪剂测量在自然丰度水平上评估藻类的初级生产和营养反应来阐明。雨水中氮的三种来源（硝态氮、铵态氮和溶解有机氮）将被追踪到具有稳定同位素的初级生产者，同时监测物种组成和光合速率。将分析藻类向微生物和浮游动物种群的初级产品转移，以研究放牧和微生物环对提高生产力的反应。一个定量模型和从大气沉降进入该地区的氮的预算将是研究的最终结果。这些结果可能对试图评估大气沉积对气候和物种多样性重要性的全球建模者有用。

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.