RAPID: Draining the landscape: Will the drop in stream and groundwater levels following dam removal increase the leaching/leakage of nitrogen (N) from riparian zones?

目前，美国各地正在拆除大量水坝，而且拆除速度还在加快。大多数大坝拆除是出于提高公共安全、减少所有者责任和改善鱼类/水生栖息地的需要。然而，很少有人关注大坝拆除对水质的影响。一般来说，水坝减缓水流的速度，同时提高河流和被称为河岸地区的河边地区的水位。无意中，这提供了一个宝贵的好处：富含碳的潮湿土壤是氮的重要过滤器，氮是水道中的主要污染物。这种自然过滤服务降低了溪水中的氮浓度，改善了水质。拆除大坝可能会破坏这种宝贵的服务，并可能增加溪流中的氮含量。这项研究将量化大坝拆除如何改变河岸土壤过滤氮的能力。结果将传达给土地所有者和自然资源机构，这将使他们在水坝拆除方面做出明智的决定，并更好地管理我们的流域。这项研究将为本科生和研究生的教育和专业发展提供一个宝贵的机会。除了在专业会议和会议上发表报告外，项目成果还将通过在社区科学咖啡馆举行的讲座向更广泛的非学术听众传播。河岸带的近地表地下水和湿润土壤条件，特别是大坝上游，增强了土壤的反硝化作用——这是河岸带过滤和去除土壤中的氮(N)的关键机制，也是氮缓冲的热点。大坝的拆除会降低地下水位，使河岸土壤暴露和干燥，并导致宝贵的反硝化生态系统服务的丧失。此外，土壤干燥可以增强矿化和硝化作用，释放土壤氮和增加水污染的过程。这可能导致河岸地带从流域氮汇转变为氮源。这一假设（大坝拆除后土壤氮泄漏增加）将在宾夕法尼亚州的奇基斯溪遗址进行测试，那里的克拉迪米尔大坝最近被拆除。将每周监测和采样两个河岸样带的溪水和地下水，以研究氮种浓度的变化。将收集沿样带和不同土壤深度的河岸土壤样本，以测量土壤N浓度的变化以及矿化、硝化和反硝化的速率。测量的过程速率以及排水土壤的面积范围将用于估计/预测大坝拆除后的N泄漏（每单位水流长度千克）。考虑到美国各地越来越多的大坝拆除，这项研究的结果将为流域管理和评估大坝拆除的利弊提供重要的新见解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

A large number of dams are currently being removed across the U.S. and at an accelerating pace. Most of the dam removals are driven by the need to increase public safety, reduce owner liability, and improve fish/aquatic habitat. However, little attention is being paid to how dam removals could influence water quality. Generally, dams slow down the flow of water and simultaneously raise the level of water in the stream and in the stream-side areas known as riparian areas. Unintentionally, this provides a valuable benefit: wet soils rich in carbon act as important filters for nitrogen, a key pollutant in waterways. This natural filtering service reduces stream water nitrogen concentrations and improves water quality. Dam removals could undermine this valuable service and potentially increase nitrogen in streams. This study will quantify how dam removal alters the capacity of riparian soils in filtering nitrogen. Results will be conveyed to landowners and natural resource agencies which will position them to make informed decisions on dam removals and better manage our watersheds. The study will provide a valuable opportunity for education and professional development for undergraduate and graduate students. In addition to presentations at professional conferences and meetings, project results will be disseminated to broader, non-academic audiences through talks at community Science Cafes.Near-surface groundwater and wet soil conditions in riparian zones, particularly upstream of dams, enhance denitrification in soils - a key mechanism by which riparian zones filter and remove nitrogen (N) from soils and act as hot spots for nitrogen buffering. Dam removals can lower groundwater levels, expose and dry riparian soils, and result in loss of valuable denitrification ecosystem services. Furthermore, drying of soils could enhance mineralization and nitrification, processes that release soil N and increase water pollution. This could result in riparian zones switching from watershed N sinks to sources. This hypothesis (increasing soil N leakage following dam removal) will be tested at the Chickies Creek site in Pennsylvania where the Krady Mill dam was recently removed. Stream water and ground waters at two riparian transects will be monitored and sampled weekly to study changes in concentration of nitrogen species. Riparian soil samples along the transects and at various soil depths will be collected to measure changes in soil N concentrations and the rates of mineralization, nitrification and denitrification. Measured process rates along with areal extent of the drained soils will be used to estimate/predict the N leakage (kg per unit stream length) following dam removal. Considering increasing dam removals across the U.S., results from this study will provide novel insights critical for watershed management and assessing the benefits and drawbacks of dam removal.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.