Collaborative Research: Ecosystem Evolution and Sustainability of Nutrient Enriched Coastal Saltmarshes

概述：盐沼提供了广泛的关键生态系统服务，但也面临多种人为威胁，包括养分富集和海平面加速上升。初级生产、分解、沉积和海平面上升之间复杂的相互作用决定了相对于海平面上升速度的临界点，超过这个临界点，沼泽可能会变成开阔的水域。硝酸盐-沿海n富集的主要形式-作为一种强大的电子受体刺激微生物分解，作为一种肥料刺激植物生长，通过关键植物和微生物过程的相互反馈有可能改变盐沼，潜在地降低相对于海平面上升的临界点。我们迫切需要了解沿海富集对盐沼的影响，部分原因是盐沼在全球范围内迅速消失，部分原因是盐沼已成为大规模恢复战略的焦点，这些战略耗资数百万至数十亿美元，用于充当沿海城市的风暴缓冲区和缓解气候变化的“蓝色”碳库。TIDE盐沼实验是一项独特的生态系统规模的试验，旨在研究养分富集如何影响生态系统的结构、功能和长期可持续性。与广为接受的盐沼模型相反，TIDE表明营养物质会导致盐沼流失；然而，关于因果关系的重要问题，以及地貌和生态系统功能是否会继续改变或在营养负荷下达到新的景观平衡，仍然没有答案。鉴于该项目迄今为止所观察到的持续变化，PI将继续进行为期13年的实验，以解决：(1)长期景观演变（自催化还是自我限制？），(2)植物机制（环境过滤是否适合地下生物量较低、耐洪水能力较差的植物？）；(3)微生物机制（NO3-是否消除了微生物的资源限制并不成比例地刺激了河岸反硝化菌/分解者？）；(4)对生态系统功能的影响（随着溪边沼泽的消失，盐沼是否保留了更少的氮？）研究人员将采用全生态系统实验操作、遗传方法、普通花园实验、生态系统组分中富集15N- no3 -添加量和δ 15N值相结合的方法来了解生态系统地貌和N循环变化的机制。该项目整合了新的研究人员来解决地貌变化、植物和微生物遗传学、基因表达、全系统生态系统养分循环和反硝化等问题。智力优势：该跨学科项目涉及生态系统、植物、微生物、生物地球化学和地质研究人员，将测试有关生态系统结构和功能控制以及营养丰富湿地的长期可持续性的基本问题。世界上许多以碎屑为基础的湿地生态系统（北方湿地、苔原湿地、咸水湿地和淡水湿地）正在出乎意料地跨越临界点，这表明有必要重新评估我们对它们对扰动反应的性质和速度的理论和理解。发展对自然生态系统中临界点的控制的预测性理解，以及这些临界点如何被人类活动改变，是生态系统科学的一个主要挑战。更广泛的影响：该项目更广泛的社会影响在于解决一个全球性的重要问题——沿海富营养化。教育方面的影响包括通过学科之间的结构化轮换和实践实地研究，加强高中到研究生的跨学科培训。与少数族裔服务机构和RUI女子学院的新伙伴关系将吸引城市、贫困和少数族裔学生。整个生态系统的实验作为一个生活实验室，为科学界的教育和研究基础设施提供支持。MBL的科学新闻项目和帕克河国家野生动物保护区将被用来向公众展示研究结果。通过与环境保护署和瓦奎特湾国家河口研究保护区共同主办的研讨会，管理外展将吸引地方、州和联邦管理人员。

Overview: Salt marshes provide a broad suite of critical ecosystem services but also face multiple anthropogenic threats including nutrient enrichment and accelerated sea-level rise. Complex interactions between primary production, decomposition, sedimentation, and sea level rise determine the tipping point relative to the rate of sea-level rise beyond which the marsh may convert to open water. Nitrate - the dominant form of coastal N-enrichment - acts as both a powerful electron acceptor stimulating microbial decomposition and as a fertilizer stimulating plant growth with the potential to transform saltmarshes through interactive feedbacks in key plant and microbial processes, potentially lowering the tipping point relative to sea-level rise. It is urgent that we understand the impacts of coastal enrichment on saltmarshes in part because of their globally rapid loss, and in part because salt marshes have become the focus of large-scale restoration strategies costing millions to billions of dollars to serve as storm buffers for coastal cities and as "blue" carbon pools to mitigate climate change. The TIDE saltmarsh experiment is a unique ecosystem-scale test of how nutrient enrichment affects ecosystem structure, function, and long-term sustainability. Contrary to well-accepted saltmarsh models, TIDE has shown that nutrients can drive saltmarsh loss; however, important questions about causality, and whether geomorphic and ecosystem function will continue to change or reach a new landscape equilibrium with nutrient loading, remain unanswered. Given the ongoing changes observed by the project to date, the PI will continue the experiment for a total of 13 years to address: (1) long-term landscape evolution (autocatalytic or self-limiting?), (2) plant mechanisms (Is environmental filtering selecting for plants with lower belowground biomass that are less flood tolerant?); (3) microbial mechanisms (Does NO3- remove resource limitation on the microbes and disproportionately stimulate creek bank denitrifiers/decomposers?); and (4) the consequences for ecosystem function (With loss of creek edge marsh, do saltmarshes retain less N?). The investigators will use a combination of whole-ecosystem experimental manipulations, genetic approaches, common garden experiments, and enriched 15N-NO3 - additions and delta 15N values in ecosystem components to understand mechanisms underlying ecosystem geomorphic and N cycle changes. This project incorporates new researchers to address questions of geomorphologic change, plant and microbial genetics, gene expression, whole-system ecosystem nutrient cycling, and denitrification.Intellectual Merit: This interdisciplinary project involving ecosystem, plant, microbial, biogeochemical, and geological researchers will test fundamental questions about controls on ecosystem structure and function and the long-term sustainability of nutrient enriched wetlands. Many detritus-based wetland ecosystems worldwide (boreal, tundra, salt- and fresh-water wetlands) are unexpectedly crossing tipping points suggesting there is a need to re-assess our theories and understanding on the nature and pace of their response to perturbation. Developing a predictive understanding of the controls on tipping points in natural ecosystems, and how these tipping points are altered by human activities, represents a major challenge in ecosystem science.Broader Impacts: The broader social impacts of this project lie in addressing a globally important issue, coastal eutrophication. The educational impacts include enhancing high school to graduate student interdisciplinary training through a structured rotation among disciplines and hands-on field research. New partnerships with minority serving institutions and a RUI women's college will engage urban, underprivileged and minority students. A whole-ecosystem experiment is supported as a living lab for education and research infrastructure for the scientific community. The MBL's Science Journalism Program and the Parker River National Wildlife Refuge will be used to showcase the results to the public. Management outreach through workshops co-hosted with EPA and the Waquoit Bay National Estuarine Research Reserve will engage local, state and federal managers.