Collaborative Research: Ecosystems on the Edge - Tidal wetland-estuary margins as buffers, reactors, and transformers of organic carbon and nitrogen

潮汐湿地是地球上最具生产力、多样性和经济重要性的生态系统之一。它们也特别容易受到人类压力和环境变化的影响。湿地含有大量的土壤有机质，是河口和沿海海洋碳和氮的重要来源，但对这些营养物质转运的过程知之甚少。该项目将通过将潮汐湿地土壤和河口之间的过程联系起来，并评估在沼泽土壤-河口系统中溶解的有机化合物在何时、何地以及如何被保留、释放和转化，来促进对潮汐沼泽-河口相互作用的理解。这项研究的结果将通过与环境保护局、国家海洋和大气管理局和国家河口研究保护区系统的合作，纳入加强监测和管理工作。该项目将改进预测湿地对河口和沿海生物、地球化学和污染反应影响的模型。该团队将与史密森尼公民科学项目和为少数民族学生服务的中学教师合作，开发K-12教育材料。专业培训将扩展到本科生，以及研究生和博士后研究人员，特别关注科学领域代表性不足的群体。本研究将测试三个关键的研究假设，这些假设对于理解沼泽土壤和潮汐湿地-河口边缘作为缓冲、反应器和溶解有机碳和氮的转换器的作用至关重要，并且可以改变我们预测湿地生态系统对河口生物学、生物地球化学和生态学的影响的能力。本文将采用综合方法来检验各种假设，这些假设结合了丰富的数据集、以过程为重点的实验和一种新的耦合水动力学-光-生物地球化学模型，以调查沼泽出口的三个尚未得到充分研究的方面，这些方面可能控制河口溶解有机质的季节性和命运：（i)土壤和孔隙水有机质组成，（ii）土壤表面的吸附-解吸，以及iii）河口水域的光和生物降解。拟议的活动从系统角度出发，涵盖广泛的沼泽环境（即不同的沼泽植被特征、土壤类型、表面积和盐度制度），提供了在一系列空间和时间尺度上扩大和评估潮汐沼泽生物地球化学通量和过程的能力。本研究结果将增加对湿地和河口系统对沿海碳氮收支的贡献的认识，并改进对湿地、河口和海岸带连续体中生态系统过程、生物地球化学循环和交换的自然和人为压力影响的预测。这些信息对于在面临加速的环境变化和持续的人类压力的情况下管理沿海地区非常有价值，特别是对于评估管理湿地恢复以减轻气候变化影响的潜力非常有价值。

Tidal wetlands are among the most productive, diverse and economically important ecosystems on Earth. They are also especially vulnerable to human pressures and environmental change. Wetlands contain large reservoirs of soil organic matter, an important source of carbon and nitrogen to estuaries and coastal oceans, but very little is known about the processes involved in the translocation of these nutrients. This project will advance understanding of tidal marsh-estuarine interactions by linking processes between tidal wetland soils and estuaries, and assessing where, when, and how dissolved organic compounds are retained, released and transformed within the marsh soil-estuarine system. Results from this study will be integrated into enhanced monitoring and management efforts through partnerships with the Environmental Protection Agency, the National Oceanic and Atmospheric Administration and the National Estuarine Research Reserve System. The project will improve models that predict the influence of wetlands on estuarine and coastal biology, geochemistry and pollution response. In collaboration with the Smithsonian Citizen Science program and teachers from middle schools serving minority students, the team will develop K-12 educational materials. Specialized training will be extended to undergraduate students, as well as graduate and postdoctoral researchers, with a particular focus on underrepresented groups in science. This study will test three key research hypotheses that are critical for understanding the role of marsh soils and tidal wetland-estuary margins as buffers, reactors, and transformers of dissolved organic C and N, and that could transform our ability to predict the influence of wetland ecosystems on estuarine biology, biogeochemistry, and ecology. An integrative approach will be used to test hypotheses that combines rich datasets, process-focused experiments, and a novel coupled hydrodynamic-photo-biogeochemical model to investigate three understudied aspects of marsh export that likely control the seasonality and fate of dissolved organic matter in estuaries: (i) soil and porewater organic matter composition, (ii) adsorption-desorption on soil surfaces, and iii) photo- and bio- degradation in estuarine waters. Proposed activities incorporate a system perspective and cover a broad range of marsh environments (i.e., different marsh vegetation characteristics, soil type, surface area and salinity regimes) providing the ability to scale up and assess tidal marsh biogeochemical fluxes and processes across a range of spatial and temporal scales. Results from this research will increase understanding of the contributions of wetlands and estuarine systems to coastal carbon and nitrogen budgets, and improve predictions of the influences of natural and man-made stresses on ecosystem processes, biogeochemical cycles and exchanges along the continuum of wetlands, estuaries and the coastal zone. This information is highly valuable to managing the coastal zone in the face of accelerated environmental change and continued human pressures and, in particular, to evaluating the potential for managed restoration of wetlands to mitigate climate change impacts.