Collaborative Research: Cryptic nitrogen cycling in the subterranean estuary

合作研究：地下河口的隐性氮循环

• 批准号: 1657801
• 负责人: Craig Tobias
• 金额: $ 16万
• 依托单位: University of Connecticut
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-05-01 至 2022-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1657801&HistoricalAwards=false
• 关键词: Collaborative; Research; Cryptic; nitrogen; cycling

Nitrogen is an important nutrient that maintains high coastal ecosystem productivity. Yet excess nitrogen delivery can cause serious water quality deterioration including harmful algal blooms, fish kills, and oxygen free dead zones. Numerous nitrogen transformations regulate the balance between nitrogen delivery and nitrogen removal in coastal environments and the majority of these reactions occur in sediments where seawater passes through the subsurface and mixes with groundwater transported from uplands. This mixing zone, referred to as the subterranean estuary, is characterized by very different geochemistry than either the seawater above it or the groundwater below it. Thus, it has the potential to host a variety of unique reactions that affect nitrogen availability to the overlying water. Scientists from the College of William and Mary, Virginia Institute of Marine Science (VIMS), and the University of Connecticut (UConn) propose to examine the importance of a cryptic nitrogen cycle, a novel and potentially widespread nitrogen cycling process in the subterranean estuary. The cryptic nitrogen cycle comprises anoxic ammonium oxidation to nitrite (anoxic nitrification) coupled with anaerobic ammonium oxidation (anammox) or denitrification producing harmless dinitrogen gas. The proposed project represents highly transformative science because it has the potential to change the current paradigm detailing operation of the biogeochemical nitrogen cycle in anoxic environments. Occurrence of the cryptic nitrogen cycle would have broad implications for the nitrogen budget of terrestrial and groundwater systems and the coastal ocean. Characterization of the cryptic nitrogen cycle will allow us to better understand interactions among the nitrogen, metals, and sulfur cycles, and potential impacts of ongoing human modification of coastal environments. Educational contribution of this project focuses on graduate and undergraduate student training. Two graduate students at VIMS and UConn will receive interdisciplinary training in microbiology, molecular ecology, and biogeochemistry while several undergraduates recruited through the VIMS REU (Research Experience for Undergraduates) Program and the UConn marine science programs will also participate in the project. In addition, three summer undergraduate interns will be recruited from Hampton University, a historically Black college, and trained to enhance minority education and research in marine science. Public outreach will be achieved through popular venues such as VIMS Marine Science Day, and the VIMS After Hours Public Lecture Series at VIMS. Tobias at UConn also provides educational contributions and outreach efforts through the UConn Marine Scholars and Early College Experience programs and an exhibit at Mystic Aquarium.A cryptic nitrogen cycle is proposed as a new process coupling anoxic nitrification to microbial nitrogen removal pathways such as anammox and denitrification. Unlike anammox, which refers to the oxidation of ammonium by nitrite to form dinitrogen (N2) gas, anoxic nitrification occurs by oxidation of ammonium in the absence of oxygen using other common chemical oxidants such as metal oxides (namely, Fe and Mn) or sulfate, abundant in many marine and coastal systems. The thermodynamic favorability of these reactions relies on coupling nitrite formed via these oxidants with anammox or denitrification. Due to the coupling, nitrite will not accumulate or be measurable in anoxic marine systems. Thus, a cryptic N cycle responsible for nitrite production can occur as a novel N transforming process in anoxic environments, serve as a vital link to N2 production, and attenuate N loads discharging from a subterranean estuary (STE). Preliminary results from a STE in the York River Estuary located in Virginia showed substantial N2 production, representing removal of 50-75% of the fixed groundwater N, in ferruginous and sulfidic zones where neither nitrite nor nitrate were detectable. Stable isotope incubation experiments using the 15N tracer and molecular analysis of microbial communities suggest that coupled anoxic nitrification and anammox processes are the dominant N2 production pathways rather than canonical denitrification in the STE. Therefore, coupled anoxic nitrification-anammox in coastal groundwater may be a major unrecognized sink for fixed nitrogen at the land-sea interface. In addition to coastal groundwater, the cryptic N cycle has potential importance in anoxic zones and ocean basins. This proposal focuses on the STE because geochemical conditions there appear optimal for the proposed reactions to occur, and our preliminary data show strong evidence for a cryptic N cycle. The proposed work uses a combined geochemical, 15N isotope tracer and microbiological approach to evaluate environmental controls on the cryptic N cycle as well as to estimate its contribution to reduction of fixed N fluxes to the coastal ocean. Four approaches are proposed: (1) Field characterization of anoxic nitrification reactions and associated microbial communities in a subterranean estuary; (2) Laboratory incubation experiments to identify hotspots of the cryptic N cycle; (3) Controlled microcosm experiments to determine geochemical controls on anoxic nitrification; and (4) in situ assessment of anoxic nitrification to estimate the importance of the cryptic N cycle in a coastal aquifer.

氮是维持沿海生态系统高生产力的重要营养元素。然而，过量的氮输送会导致严重的水质恶化，包括有害的藻华，鱼类死亡和无氧死区。在沿海环境中，许多氮转化调节氮输送和氮去除之间的平衡，并且这些反应中的大多数发生在海水穿过地下并与从高地输送的地下水混合的沉积物中。这一混合区被称为地下河口，其特征是与其上方的海水或其下方的地下水具有非常不同的地球化学性质。因此，它有可能发生各种独特的反应，影响上覆水的氮可用性。 来自威廉和玛丽学院、弗吉尼亚海洋科学研究所（VIMS）和康涅狄格大学（UConn）的科学家建议研究一个神秘的氮循环的重要性，这是一个在地下河口新颖且可能广泛的氮循环过程。隐氮循环包括缺氧氨氧化为亚硝酸盐（缺氧硝化），再加上厌氧氨氧化（厌氧氨氧化）或反硝化产生无害的二氮气体。拟议的项目代表了高度变革性的科学，因为它有可能改变目前的模式，详细说明缺氧环境中地球化学氮循环的运作。隐氮循环的发生将对陆地和地下水系统以及沿海海洋的氮收支产生广泛的影响。对神秘氮循环的表征将使我们能够更好地了解氮、金属和硫循环之间的相互作用，以及人类对沿海环境持续改造的潜在影响。该项目的教育贡献侧重于研究生和本科生培训。VIMS和UConn的两名研究生将接受微生物学，分子生态学和生物化学的跨学科培训，而通过VIMS REU（本科生研究经验）计划和UConn海洋科学计划招募的几名本科生也将参与该项目。此外，将从历史上的黑人学院汉普顿大学招聘三名暑期本科实习生，并对他们进行培训，以加强少数民族在海洋科学方面的教育和研究。将通过VIMS海洋科学日和VIMS下班后公开讲座系列等受欢迎的场所实现公众宣传。康州大学的托比亚斯还通过康州大学海洋学者和早期大学体验计划以及神秘水族馆的展览提供教育贡献和推广工作。提出了一种隐氮循环作为将缺氧硝化与微生物脱氮途径（如厌氧氨氧化和反硝化）耦合的新工艺。与厌氧氨氧化不同，厌氧氨氧化是指铵被亚硝酸盐氧化形成二氮（N2）气体，缺氧硝化是在没有氧气的情况下使用其他常见的化学氧化剂，如金属氧化物（即铁和锰）或硫酸盐，在许多海洋和沿海系统中大量氧化铵。这些反应的热力学稳定性依赖于通过这些氧化剂与厌氧氨氧化或反硝化作用形成的亚硝酸盐的偶联。由于耦合，亚硝酸盐不会积累或在缺氧海洋系统中可测量。因此，一个神秘的N循环负责亚硝酸盐的生产可以发生作为一种新的N转化过程中缺氧的环境中，作为一个重要的环节，以N2生产，并衰减N负荷排放的地下河口（STE）。STE在位于弗吉尼亚州的约克河口的初步结果显示，大量的N2生产，代表去除50-75%的固定地下水N，在含铁和硫化物的区域，既没有亚硝酸盐也没有硝酸盐检测。稳定同位素培养实验，使用15 N示踪剂和微生物群落的分子分析表明，耦合缺氧硝化和厌氧氨氧化过程中占主导地位的N2生产途径，而不是典型的反硝化在STE。 因此，耦合缺氧硝化厌氧氨氧化在沿海地下水可能是一个主要的未被认识到的固定氮在陆地-海洋界面汇。除了沿海地下水，隐氮循环在缺氧区和海洋盆地具有潜在的重要性。这项建议的重点是STE，因为地球化学条件出现最佳的建议的反应发生，我们的初步数据显示了一个神秘的N循环的有力证据。拟议的工作使用相结合的地球化学，15 N同位素示踪剂和微生物的方法来评估环境控制的隐N循环，以及估计其贡献减少固定N通量的沿海海洋。提出了四种办法：（1）缺氧硝化反应和相关的微生物群落在地下河口的现场表征;（2）实验室培养实验，以确定潜在的N循环的热点;（3）受控的微观实验，以确定缺氧硝化的地球化学控制;（4）缺氧硝化的原位评估，以估计潜在的N循环在沿海含水层的重要性。