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，但也面临着多种人为威胁，包括营养物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率的临界点，超过该临界点沼泽可能会转变为开放水域。硝酸盐是沿海富氮的主要形式，它既是刺激微生物分解的强大电子受体，又是刺激植物生长的肥料，有可能通过关键植物和微生物过程的交互反馈来改造盐沼，从而有可能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重点，耗资数百万至数十亿美元作为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测试，旨在测试营养物富集如何影响生态系统结构、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变化或与养分负荷达到新的景观平衡，仍然没有答案。鉴于该项目迄今为止观察到的持续变化，PI将继续该实验总共13年，以解决：（1）长期景观演化（自催化或自限制？），（2）植物机制（环境过滤是否选择地下生物量较低、耐洪能力较差的植物？）； (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溪岸反硝化器/分解器？）； (4) 对生态系统功能的影响（随着溪边沼泽的消失，盐沼保留的氮会减少吗？）。研究人员将结合使用整个生态系统实验操作、遗传方法、常见花园实验以及生态系统成分中丰富的 15N-NO3 添加和 Delta 15N 值，以了解生态系统地貌和氮循环变化的机制。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反硝化等问题。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有关生态系统结构和功能控制以及养分丰富湿地长期可持续性的基本问题。全世界许多以碎屑为基础的湿地生态系统（寒带、苔原、咸水和淡水湿地）出乎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其对扰动响应的性质和速度的理解。对自然生态系统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的一项重大挑战。 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重要问题，即沿海富营养化。教育影响包括通过学科间的结构化轮换和实践实地研究来加强高中到研究生的跨学科培训。与少数民族服务机构和 RUI 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。支持全生态系统实验作为科学界教育和研究基础设施的生活实验室。 MBL 的科学新闻计划和帕克河国家野生动物保护区将用于向公众展示研究结果。通过与 EPA 和瓦阔伊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、州和联邦管理人员参与。

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.