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多产、最多样和最重要的经济生态系统之一。它们还特别容易受到人类压力和环境变化的影响。湿地含有大量土壤有机质，是河口和沿海海洋碳和氮的重要来源，但人们对这些营养物质的转移过程知之甚少。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，并评估溶解的有机化合物在沼泽土壤-河口系统中的保留、释放和转化的地点、时间和方式，来促进对潮汐湿地-河口相互作用的了解。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储备系统的伙伴关系纳入加强的监测和管理工作。该项目将改进预测湿地对河口和海岸生物、地球化学和污染反应的影响的模型。该团队将与史密森公民科学计划和为少数族裔学生服务的中学教师合作，开发K-12教育材料。专门培训将扩展到本科生以及研究生和博士后研究人员，特别侧重于科学中代表性不足的群体。这项研究将检验三个关键的研究假说，这三个假说对于理解沼泽土壤和潮汐湿地-河口边缘作为溶解有机C和N的缓冲器、反应器和转换器的作用至关重要，并可能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。我们将使用一种综合的方法来检验假设，该假设结合了丰富的数据集、以过程为中心的实验和一个新的水动力-光-生物地球化学耦合模型，以研究可能控制河口溶解有机质的季节性和归宿的沼泽输出的三个未被研究的方面：(I)土壤和孔隙水有机质组成，(Ii)在土壤表面的吸附-解吸，以及(Iii)河口水域的光和生物降解。拟议的活动纳入了系统观点，涵盖了广泛的沼泽环境(即不同的沼泽植被特征、土壤类型、表面积和盐分制度)，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。这项研究的结果将增进对湿地和河口系统对沿海碳、氮收支的贡献的理解，并改进对自然和人为压力对湿地、河口和海岸地带连续统的生态系统过程、生物地球化学循环和交换的影响的预测。这些信息对于面对加速的环境变化和持续的人类压力管理沿海地区，特别是评估有管理地恢复湿地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.