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

概述：盐沼提供广泛的关键生态系统服务，但也面临多种人为威胁，包括营养丰富和海平面加速上升。初级生产力、分解、沉积和海平面上升之间的复杂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，沼泽可能会转变为开阔水域。硝酸盐--沿海氮素浓缩的主要形式--既是刺激微生物分解的强大电子受体，也是一种肥料，有可能通过关键植物和微生物过程中的交互反馈改变盐沼，从而降低相对于海平面上升的临界点。我们迫切需要了解沿海浓缩对盐沼的影响，部分原因是它们在全球范围内迅速丧失，部分原因是盐沼已成为大规模恢复战略的重点，这些战略耗资数百万至数十亿美元，作为沿海城市的风暴缓冲器和缓解气候变化的“蓝色”碳池。潮汐盐沼实验是一项独特的生态系统规模测试，旨在测试营养丰富如何影响生态系统的结构、功能和长期可持续性。与公认的盐沼模型相反，潮汐已经表明营养物质可以驱动盐沼的损失；然而，关于因果关系以及地貌和生态系统功能是否会随着养分负载继续变化或达到新的景观平衡的重要问题仍未得到回答。考虑到该项目到目前为止观察到的持续变化，PI将继续进行总共13年的实验，以解决：(1)长期的景观演变(自动催化或自我限制？)，(2)植物机制(环境过滤是否选择地下生物量较低的植物，这些植物对洪水的耐受性较差？)；(3)微生物机制(NO3-是否消除对微生物的资源限制，并不成比例地刺激河岸反硝化细菌/分解者？)；(4)对生态系统功能的影响(随着小溪边缘沼泽的丧失，盐沼是否保留更少的氮？)。研究人员将结合全生态系统实验操作、遗传方法、普通花园实验以及丰富的生态系统组成部分中的15N-N3-加成和增量15N值来了解生态系统地貌和N循环变化的机制。该项目吸收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脱氮等问题。智力价值：这个涉及生态系统、植物、微生物、生物地球化学和地质研究人员的跨学科项目将测试关于生态系统结构和功能的控制以及营养丰富的湿地的长期可持续性的基本问题。世界各地许多以碎屑为基础的湿地生态系统(北方、苔原、咸水和淡水湿地)出人意料地跨越了临界点，这表明有必要重新评估我们的理论和对它们对扰动的反应的性质和速度的理解。发展对自然生态系统中临界点的控制以及人类活动如何改变这些临界点的预测性理解，是生态系统科学中的一项重大挑战。广泛的影响：该项目的更广泛的社会影响在于解决一个全球重要的问题--沿海富营养化。教育影响包括通过学科间有组织的轮换和实践实地研究，加强从高中到研究生的跨学科培训。与少数民族服务机构和一所瑞女子学院的新合作伙伴关系将吸引城市、贫困和少数民族学生。全生态系统实验作为科学界教育和研究基础设施的活实验室得到支持。MBL的科学新闻计划和帕克河国家野生动物保护区将向公众展示成果。通过与环境保护局和瓦科伊特湾国家河口研究保护区共同举办的研讨会，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.