Collaborative Research: Microbial Regulation of Greenhouse Gas N2O Emission from Intertidal Oyster Reefs

知识价值：牡蛎礁是生物地球化学热点和突出的河口栖息地，提供了不成比例的生态功能。悬食东方牡蛎（Crassostrea virginica）能够过滤水中的营养物质和颗粒，并将其沉积在沉积物中，从而改善水质，减少富营养化。这些沉积物的再矿化可能会增强沉积物的反硝化作用，从而促进潮汐河口的氮去除。然而，牡蛎礁功能的科学基础在各种研究中受到挑战。此外，最近对滤食性无脊椎动物的研究报告称，作为肠道微生物不完全反硝化的最终产物，氧化亚氮（N2O）是一种温室气体。C. virginica可能是潮间带栖息地N2O通量的另一个来源。初步工作表明，单个牡蛎产生大量的一氧化二氮。高密度牡蛎礁估计的N2O产量可能超过从某些河口测量的N2O通量。随着N2O排放的新发现和富营养化控制的不确定性，牡蛎礁恢复的生态价值可能变得模棱两可。本项目将量化N2O通量，以了解控制牡蛎礁N2O排放的因素。将研究沉积N过程，建立牡蛎礁N模型，以估计潮汐溪河口相对于其他N循环过程的N2O排放。PIs假设潮间带牡蛎礁是河口生态系统N2O排放的一个重要来源，排放的大小可能与水质有关。如果证实牡蛎礁有大量的N2O通量，则应重新评估牡蛎礁恢复的生态效益。这个跨学科的研究团队包括一名微生物生态学家、一名生物地球化学家、一名生态学家和一名生态系统建模师。他们将利用稳定同位素和分子微生物学技术量化牡蛎N2O产量，阐明牡蛎和沉积物N2O排放的微生物来源，并估计牡蛎礁N2O通量的季节性变化。本研究的测量结果将被整合到一个耦合的牡蛎生物能量-沉积物生物地球化学模型中，以比较牡蛎礁上N循环的系统水平速率作为牡蛎密度和水质的函数。建模结果将用于评估与氮循环相关的牡蛎恢复的相对权衡。他们希望提供以下最终产品：1)估计牡蛎礁作为河口温室气体的额外来源的年N2O通量，2)更好地了解影响潮汐河口N2O和N2通量的环境和微生物因素，3)对牡蛎恢复对水质改善和生态系统功能的影响的变革性知识，4)直接指导以改善水质为目标的牡蛎恢复项目。5)为研究和修复规划提供建模工具。更广泛的影响将通过不同的教育组成部分和外联活动表现出来。四名主要研究人员将为至少三名攻读硕士或博士学位的研究生提供跨学科培训。额外的教育影响将在课堂上和个人本科生研究项目中完成。校际小组将在此研究基础上提供一学期的本科实地体验。该项目将为高中生提供参与牡蛎孵化实验和监测N2O生成的研究经验。生态模型将被翻译成一个用户友好的在线工具，供其他科学家、修复管理者和教育工作者使用，并开发相关的推广材料。该项目的数据将被用作“同位素生物地球化学和反应与运输”课程的习题集。将通过妇女和人数不足群体海洋科学研究生奖学金，在研究生一级实现对科学领域人数不足群体的承诺。

Intellectual Merit: Oyster reefs are biogeochemical hot spots and prominent estuarine habitats that provide disproportionate ecological function. Suspension-feeding eastern oysters, Crassostrea virginica, are capable of improving water quality and diminishing eutrophication by filtering nutrients and particles from the water and depositing them in the sediments. Remineralization of these deposits may enhance sedimentary denitrification that facilitates nitrogen removal in tidal estuaries. However, the scientific underpinning of oyster reef function has been challenged in various studies. In addition, recent studies of filter feeding invertebrates reported the production of nitrous oxide (N2O), a greenhouse gas, as an end product of incomplete denitrification by gut microbes. C. virginica could be another source of N2O flux from intertidal habitats. Preliminary work indicated substantial N2O production from individual oysters. The estimated N2O production from high density oyster reefs may exceed the N2O flux measured from some estuaries. With the new discovery of N2O emission and uncertainty regarding eutrophication control, the ecological value of oyster reef restoration may become equivocal. This project will quantify N2O fluxes to understand the factors controlling N2O emission from oyster reefs. Sedimentary N processes will be examined to develop an oyster reef N model to estimate N2O emission from tidal creek estuaries relative to other N cycling processes. The PIs hypothesize that intertidal oyster reefs are a substantial source of N2O emission from estuarine ecosystems and the magnitude of emission may be linked to water quality. If substantial N2O flux from oyster reefs is validated, ecological benefits of oyster reef restoration should be reevaluated. This interdisciplinary research team includes a microbial ecologist, a biogeochemist, an ecologist and an ecosystem modeler. They will utilize stable isotope and molecular microbiological techniques to quantify oyster N2O production, elucidate microbial sources of N2O emission from oysters and sediments, and estimate seasonal variation of N2O fluxes from oyster reefs. Measurements from this study will be integrated into a coupled oyster bioenergetics-sediment biogeochemistry model to compare system level rates of N cycling on oyster reefs as a function of oyster density and water quality. Modeling results will be used to assess the relative trade-­offs of oyster restoration associated with N cycling. They expect to deliver the following end products:1) estimation of annual N2O flux from oyster reefs as an additional source of greenhouse gases from estuaries, 2) a better understanding of the environmental and microbial factors influencing N2O and N2 fluxes in tidal estuaries, 3) transformative knowledge for the effect of oyster restoration on water quality enhancement and ecosystem function, 4) direct guidance for oyster restoration projects whose goals include water quality enhancement, and 5) a modeling tool for use in research and restoration planning. Broader impacts will be manifested through diverse educational components and outreach. Four principal investigators will provide interdisciplinary training to at least three graduate students seeking a M.S. or Ph.D. Additional educational impacts will be accomplished both in the classroom and through individual undergraduate research projects. The inter-­institutional group will provide semester long undergraduate field experiences based on this study. The project will provide research experience for high school students in which they participate in oyster incubation experiments and monitor N2O production. The ecological model will be translated into a user-­friendly, online tool for use by other scientists, restoration managers, and educators, and develop related outreach material. Data from the project will be used as problem sets in a "Isotope Biogeochemistry and Reaction and Transport" course. A commitment to underrepresented groups in the sciences will be realized at the graduate level through a Graduate Scholarship in Marine Sciences for Women and Underrepresented Groups.