Collaborative Research: MSB: Impact of sea level rise on sedimentary nitrogen removal processes in tidal freshwater ecosystems

河流和河口等潮汐淡水生态系统位于陆地和海洋的交界处。这些生态系统提供重要的自然服务，包括初级生产、养分分配和调节以及废物管理-这些服务因气候变化而面临风险。气候变化的两个方面，即海平面上升和一些流域降水量减少，将使淡水-盐水混合区的位置移向上游河流，并不断增加对淡水生境的盐分侵入。据预测，到2100年，海平面将上升100厘米，海平面本身就可能对淡水生态系统产生多重影响，包括直接的毒性影响、生境退化和养分循环的改变。盐度的增加也可能对淡水生境的氮（N）动态产生重大影响。硝化作用（氨转化为硝酸盐）和反硝化作用（硝酸盐转化为二氮）是控制过量氮负荷引起的富营养化强度和持续时间的关键微生物过程。盐度入侵可能会降低微生物的N去除能力，硝化和反硝化作用由于底物限制和生理抑制而降低。这可能导致河流和河口长期富营养化和缺氧。或者，厌氧氨氧化（anammox;铵和亚硝酸盐转化为二氮气体）可能成为一个更重要的微生物脱氮过程，并有助于恢复淡水沉积物中的N去除能力，因为anammox细菌可以容忍盐度的增加。该项目将研究1）厌氧氨氧化在潮汐淡水沉积物中的重要性，2）盐度对淡水厌氧氨氧化细菌和沉积物氮循环的影响，以及3）受海平面上升威胁的沉积物群落中替代氮去除途径的预测。拟议的研究将整合分子微生物技术，化学示踪方法和数学模型，以检查沉积物N去除过程中的恐惧角河和北卡罗来纳州的新河。该提案将带来以下好处和成果：1）揭示潮汐淡水沉积物中参与氮去除过程的微生物群落的结构和活性，2）确定沉积物群落对海水入侵的差异响应，3）了解海平面上升对淡水生态系统沉积物氮去除过程的影响，4）预测了海平面上升过程中淡水生态系统净氮去除能力的一个关键微生物过程。该项目还将深入了解淡水沉积物群落在海平面上升威胁下的微生物反应。跨学科的方法将提供深入了解社区结构和活动之间的联系，以及河流沉积氮循环的盐度影响。更广泛的影响将通过北卡罗来纳州威尔明顿大学（UNCW）和康涅狄格大学的各种教育组成部分、推广和改善研究基础设施来体现。三个PI（微生物生态学家，微生物地球化学家和生态系统建模）将提供跨学科的培训，至少有三个寻求硕士研究生。或博士℃下额外的教育影响将在课堂上完成，并通过在两个机构的个别本科生研究项目。高中生的研究经验将通过包括UNCW“夏季海洋风险投资”和“海洋17”计划中的项目来实现。高中生将参加DNA分析和围隔实验。PI将为学生提供有关微生物氮循环的讲座，并设计为期三天的实验室和实地课程，以检测和测量海洋17营地期间的反硝化作用。本研究所招募的研究生将担任高中生的助教。该计划将以夏季创业研讨会结束，学生们将展示他们的工作。将通过与当地公民团体（NC-Coastal Ocean Federation）合作招募志愿者参与采样巡航和水监测计划，并利用现有的UNCW“Planet Ocean”系列讲座作为公共平台来促进外展讨论沿海水资源问题和行动。

Tidal freshwater ecosystems such as rivers and estuaries are located at the interface between land and sea. These ecosystems provide important natural services including primary production, nutrient distribution and regulation, and waste management - services that are at risk due to climate change. Two aspects of climate change, sea level rise and lower precipitation in some watersheds, will shift the location of freshwater-saltwater mixing zones to upper rivers and continuously increase salinity intrusion into freshwater habitats. Sea level is predicted to rise up to 100 cm by 2100, and by itself can have multiple impacts on freshwater ecosystems, including direct toxic effects, habitat degradation and alteration of nutrient cycles. Salinity increases may also have significant effects on the nitrogen (N) dynamics of freshwater habitats. Nitrification (ammonia conversion to nitrate) and denitrification (nitrate conversion to dinitrogen) are key microbial processes controlling the intensity and duration of eutrophication caused by excess N loading. Salinity intrusion might diminish microbial N removal capacity in freshwater sediments as nitrification and denitrification are reduced due to substrate limitation and physiological inhibition. This could result in prolonged eutrophication and hypoxia at rivers and estuaries. Alternatively, anaerobic ammonium oxidation (anammox; ammonium and nitrite conversion to dinitrogen gas) may become a more important microbial N removal process and help recover N removal capacity in freshwater sediments since anammox bacteria can tolerate salinity increases. This project will study 1) the importance of anammox in tidal freshwater sediments, 2) the effects of salinity on freshwater anammox bacteria and the sedimentary N cycle, and 3) predictions of an alternative N removal pathway in sedimentary communities threatened by sea level rise. The proposed research will integrate molecular microbial techniques, chemical tracer methods and mathematical models to examine sedimentary N removal processes in the Cape Fear River and New River of North Carolina. This proposal will result in the following benefits and outcomes; 1) revealing the structures and activities of microbial communities involved in N removal processes in tidal freshwater sediments, 2) determining differential responses of sediment communities to seawater intrusion, 3) understanding the impacts of sea level rise on sedimentary N removal processes in freshwater ecosystems, 4) predicting a key microbial process for net N removal capacity of freshwater ecosystems experiencing sea level rise. This project will also provide an in-depth understanding of microbial responses in freshwater sediment communities under threat of sea level rise. Interdisciplinary approaches will provide insight into the linkages between community structure and activity as well as salinity effects on riverine sedimentary N cycling. Broader impacts will be manifested through diverse educational components, outreach, and improved research infrastructure at the University of North Carolina Wilmington (UNCW) and the University of Connecticut. Three PIs (microbial ecologist, biogeochemist and ecosystem modeler) will provide interdisciplinary training to at least three graduate students seeking a M.S. or Ph.D. degree. Additional educational impact will be accomplished both in the classrooms and through individual undergraduate research projects at the two institutions. Research experience for high school students will be achieved by including the project within the UNCW "Summer Ocean Ventures" and "Ocean17" programs. The high school students will participate in DNA analysis and mesocosm experiments. The PI will provide a lecture on the microbial nitrogen cycle to the students and design three days of laboratory and field courses to detect and measure denitrification during the Ocean 17 camp. The graduate students recruited for this proposed research will act as teaching assistants for the high school students. The program will culminate with a Summer Ventures Symposium where students will present their work. Outreach will be facilitated by partnering with a local citizens group (NC-Coastal Ocean Federation) to recruit volunteers to participate in sampling cruises and water monitoring program, and by using the existing UNCW "Planet Ocean" lecture series as a public platform to discuss coastal water resources issues and actions.