Collaborative Research: Low-head milldams as hotspots for denitrification and nitrogen consumption: Hydrologic and biogeochemical controls

合作研究：低水头水坝作为反硝化和氮消耗的热点：水文和生物地球化学控制

• 批准号: 1929753
• 负责人: Arthur Gold
• 金额: $ 11.26万
• 依托单位: University of Rhode Island
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-08-01 至 2022-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1929753&HistoricalAwards=false
• 关键词: Collaborative; Research; Low; head; milldams

Milldam removals have increased in recent years with the highest removal rate in the mid-Atlantic US. The primary motivation for dam removals has been to improve fish passage and habitat, enhance safety for recreational users, and reduce financial liability. Few studies have however studied how dam removals could influence water quality. Dams tend to back-up and slow down stream water and raise water levels in the streams and the adjacent soils. This provides an unintended benefit of enhancing the natural filtering service of streamside soils and forests for nitrogen, a key pollutant of our nation's waterways. Thus, dam removals could undermine this valuable filtering service and increase the cost of cleaning our waterways. This study will investigate the key processes by which milldams enhance water quality in streams and streamside forests. Results from this study will be conveyed to watershed managers and natural resource agencies responsible for water quality management and dam removals. This knowledge will help them make better and more informed decisions on dam removals. The study will also provide valuable educational experience for two graduate and one undergraduate student from the University of Delaware. A local environmental historian will work with the undergraduate student and document how milldams influenced stream conditions back in the 1700-1900s through study of historic photographs, documents, and property information.Milldams reduce stream and groundwater flow velocities and increase groundwater levels upstream of the dams. High groundwater levels in riparian zones create hotspots for denitrification and an increased opportunity for nitrogen (N) removal. Similarly, increased residence time in streams and deposition of fine sediments and organic matter upstream of the dam enhances the loss of N via instream denitrification. Low-head milldams create a zone of hydrologic transition/divergence in riparian soils that compliments the riverine discontinuum concept proposed for streams. These hypotheses will be tested for three existing, sequential low-head mill dam sites on White Clay Creek in Delaware. Groundwater wells and associated chemical sampling will characterize the groundwater mixing regime. Stream assays and measurements will help characterize the in-stream processes and changes. Denitrification, nitrification and mineralization incubations on stream sediments and riparian soils will quantify N processing and consumption. These data will be integrated to develop a new, coupled, conceptual model for stream and riparian processes and mixing regimes upstream of milldams. This will be the first study to investigate how existing milldams affect riparian groundwater hydrology and water quality. This research will also provide important insights into hydrologic and biogeochemical conditions associated with stagnant or pooled waters or "lentic" river regimes. These conditions certainly existed for the dammed streams during the colonial and post-colonial era, but also exist today in modern, disconnected, and urbanized stream networks. If this work shows that riparian zones and streams near milldams are indeed hotspots and sinks for N removal, the benefits of dam removal for habitat, safety, and natural flow regimes will have to be weighed against the potential downside of losing valuable water quality ecosystem services for N removal. Results from this study will be presented at scientific meetings, published in refereed journals, and will also be conveyed to the broader community and stakeholders through Science Cafes and community charrettes.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.

近年来，Milldam的拆卸率有所增加，而美国中部美国的去除率最高。大坝去除的主要动机是改善鱼类通道和栖息地，提高娱乐用户的安全，并减少财务责任。但是，很少有研究研究大坝的去除方式如何影响水质。大坝倾向于备份并放慢溪流水，并提高溪流和相邻土壤中的水位。这为增强了氮和森林的自然过滤服务提供了一个意想不到的好处，氮是我们国家水道的关键污染物。因此，大坝的去除可能会破坏这种有价值的过滤服务，并增加清洁水道的成本。这项研究将调查米尔丹（Milldams）在溪流和溪流森林中提高水质的关键过程。这项研究的结果将被传达给负责水质管理和大坝去除的流域经理和自然资源机构。这些知识将帮助他们在大坝去除方面做出更好，更明智的决定。这项研究还将为特拉华大学的两名研究生和一名本科生提供宝贵的教育经验。当地的环境历史学家将与本科生合作，并通过研究历史照片，文档和物业信息来记录米尔丹如何影响1700 - 1900年代的流条件。Milldams降低了溪流和地下水流量速度并增加了大坝上游的地下水水平。河岸地区的高地下水水平创造了用于反硝化的热点，并增加了去除氮的机会。同样，大坝上游的流中心和有机物的沉积时间增加，通过仪表式硝化增强了n的损失。低头米尔丹在河岸土壤中创造了一个水文过渡/差异区域，以补充河流不中间的河流概念。这些假设将在特拉华州的White Clay Creek上测试三个现有的，连续的低头磨坊位点。地下水井和相关的化学采样将表征地下水混合体。流分析和测量将有助于表征流入过程和变化。溪流沉积物和河岸土壤上的硝化，硝化和矿化孵育将量化N加工和消费。这些数据将集成，以开发一种新的，耦合的，概念模型，用于流和河岸过程，并在Milldams上游混合制度。这将是第一项研究现有米尔丹如何影响河岸地下水水文学和水质的研究。这项研究还将提供有关与停滞或汇集水或“莱特式”河流政策相关的水文和生物地球化学条件的重要见解。在殖民时代和后殖民时代，这些疾病肯定存在于堵塞的溪流中，但今天也存在于现代，脱节和城市化的流网络中。如果这项工作表明，米尔丹附近的河岸区和溪流确实是热点和下沉的n，则必须权衡去除栖息地，安全性和自然流动机制的大坝去除的好处，与失去有价值的水质生态系统服务的潜在缺点。这项研究的结果将在科学会议上介绍，该会议上发表在裁判期刊上，还将通过科学咖啡馆和社区骗局传达给更广泛的社区和利益相关者。该奖项反映了NSF的法定使命，并认为通过基金会的知识分子和更广泛的影响，可以通过评估来进行评估。