RAPID/Collaborative Research: Estuarine dam removal as an ecosystem disturbance: Examining the impacts of seawater intrusion on functional stability of benthic N cycle communities

大型水坝(15米高)是对流域的主要人为干扰，改变了河流生态系统的结构和功能。纳洞河是受河口大坝影响较大的流域之一，大坝是为了阻止潮汐海水交换而修建的。1987年修建时，大坝使下游河流生态系统发生了戏剧性的变化，将该地区变成了一个人造淡水水库。河流流量的变化导致季节性有害藻类大量繁殖和水质退化。人们对这些负面影响的担忧与日俱增，加上相关的社会和经济需求，导致通过拆除大坝来恢复河流生态系统。大坝的拆除将通过一系列事件以受控的方式完成，这些事件打开了大坝的大门，从而允许海水入侵上游生态系统。这为研究海水入侵对淡水生态系统的影响提供了一个独特而直接的机会。这一系列计划中的大坝开口可以有效地用作大规模、史无前例的、可操控的生态系统实验。这个快速项目利用这一独特的机会来研究对河流中程序性海水入侵做出反应的沉积物微生物群落。该项目将包括为本科生和研究生提供培训机会，结果将通过公开讲座和河流研究人员的科学网络传播。本项目旨在研究纳洞河底泥氮(N)循环群落对海水入侵扰动的功能稳定性，该河流通过一系列大坝闸门的开启进行除坝。包括后基因组、后转录和后蛋白质组学在内的多组学方法将被用来评估一个群落中单个N代谢的敏感性和恢复力，而N循环过程(通量和速率)的测量，包括反硝化和异化硝酸盐还原为铵，揭示整个群落的代谢对海水入侵的响应。这是一个独特的、变革性的项目，旨在确定在淡水生态系统中暴露于程序化海水入侵的社区内不同新陈代谢的功能稳定性。多组学和生物地球化学相结合的测量将提供从基因到个体生物体再到群落水平不同系统水平上的敏感性和复原力的新知识。沉积物群落中的异化N循环代谢被选为微生物功能的模型，因为底栖N循环对于减轻过量N负荷至关重要，而过量N负荷是导致富营养化的原因之一。鉴于底栖生物N循环的重要性，海水入侵对沉积物N循环群落及其功能的影响主要通过微宇宙和中观系统等异地实验设计或沿河流和河口盐度梯度的实地调查来研究。这第一个项目是第一个生态系统规模的操作，研究了沉积物N循环群落对海水入侵的反应。两名研究生将参与该项目，并将接受多基因组学和生物地质化学方法方面的培训。该项目还将包括在这两个机构对本科生的培训活动，在公共外展讲座中传播结果，并通过世界动态河流系统水生生物地球化学观测网络(WHONDRS)。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Large dams ( 15m high) are a major man-made disturbance to watersheds altering the structure and function of river ecosystems. The Nakdong River is one of the watersheds heavily affected by the dam constructed at the mouth of the river to stop tidal seawater exchange. When it was built in 1987, the dam caused dramatic shifts in lower river ecosystems converting the area to a man-made freshwater reservoir. The alteration of river water flows resulted in seasonal harmful algal blooms and water quality degradation. Increasing concerns about these negative impacts along with associated social and economic demands have led to restoring the river ecosystem by removing the dam. The dam removal will be done in a controlled way through a series of events that open the dam's gates, thereby allowing seawater intrusion into upstream ecosystems. This provides a unique and immediate opportunity to study the impacts of seawater intrusion on a freshwater ecosystem. The series of planned dam openings can be effectively used as a large-scale, unprecedented, manipulative ecosystem experiment. This RAPID project takes advantage of this unique opportunity to study the sediment microbial communities responding to the programmed seawater intrusion in the river. The project will include training opportunities for undergraduate and graduate students, and results will disseminated via public lectures and a scientific network for river researchers. This project aims to study the functional stability of sediment nitrogen (N) cycling communities responding to the disturbance of seawater intrusion in the Nakdong River, where dam removal is in progress via a series openings of dam gates. Multi-omic approaches including metagenomic, metatranscriptomic and metaproteomic analyses will be conducted to evaluate both sensitivity and resilience of individual N metabolisms in a community, while the measurements of N cycling processes (fluxes and rates), including denitrification and dissimilatory nitrate reduction to ammonium, reveal a whole community metabolism responding to the seawater intrusion. This is a unique and transformative project to determine the functional stability of different metabolisms within the community exposed to a programmed seawater intrusion in a freshwater ecosystem. The combined multi-omics and biogeochemical measurements will provide novel knowledge of sensitivity and resilience in different systematic levels from genes to individual organisms to the community level. Dissimilatory N cycling metabolisms in sediment communities are selected as a model of microbial functions since benthic N cycling is critical to attenuate excess N loading, a cause of eutrophication. Given the importance of benthic N cycle, the impacts of seawater intrusion on sediment N cycling communities and their functions have been mainly examined with ex-situ experimental designs such as microcosms and mesocosms or field survey along salinity gradients of rivers and estuaries. This first project represents the first ecosystem-scale manipulation examining sediment N cycling communities responding to seawater intrusion. Two graduate students will be involved in the project and will be trained in multi-omic and biogeochemcial methods. The project will also include training activities for undergraduates at the two institutions, dissemination of results in public outreach lectures and via the Worldwide Hydrobiogeochemical Observatory Network for Dynamic River Systems (WHONDRS).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.