Collaborative Research: Linking Hydrogeomorphology And Denitrification in the Tidal Freshwater Region of Coastal Streams

合作研究：将沿海河流潮汐淡水区的水文地貌和反硝化联系起来？近几十年来，土地利用的变化和人口密度的增加加快了营养物质(特别是氮)从陆源向水生生物群的输送速度。人类现在向水生圈和生物圈贡献的活性氮(N)比所有其他自然氮源的总和还要多。水生栖息地反过来以滋扰藻类大量繁殖、物种组成变化、对鳍和贝类资源的影响以及有害的经济后果来应对。随着溪流和河流越来越接近氮饱和，越来越多的氮污染被输出到沿海边缘，在那里它促进了缺氧事件的严重程度和持续时间的扩大。了解N在整个水生连续体(如小溪、河流和河口)中的去向和迁移，对于确定对N输入特别敏感的区域和作为N去除热点的区域是必要的。对控制N反应的水文和化学机制的了解为指导营养管理战略和提高这些环境减少N负荷的自然能力提供了基础。反硝化作用的测量是代表氮的绝对衰减的唯一机制，已经在广泛的水生生态类型中进行了检验。然而，水域连续体的一个特殊部分，潮汐淡水河流和溪流，通常没有被调查。将高地溪流和河流与河口连接起来，我们认为潮汐淡水溪流具有独特的水文、地貌和化学反应能力，相对于水生连续体的任何其他组成部分，它们都最有利于氮的去除。此外，我们提出，在非潮汐系统中，只需通过诱导准潮汐水文状况(即，通过产生有节奏的水位上升和下降)，就可以产生增强的氮去除。调查人员建议将美国东南部沿海平原溪流的广泛水化学监测工作与一系列独特的化学示踪研究和溪流建模结合起来。所有工作应在自然和水文条件下就地进行。潮汐溪流是美国东南部的主要水生特征，这项拟议的工作将有助于确定它们在多大程度上是广泛地理范围内氮去除的热点。这项研究代表着一项联邦和学术合作伙伴关系，将提供更好的理解分水岭的营养物质负荷如何转化为大陆边缘的生态系统反应。这种性质的工作对于改进对生境对人类干扰和/或恢复影响的反应的预测、评估水生生境的复原力、完善营养物质负荷的调控目标至关重要。水文学和化学如何相互作用来调节氮的处理，这一机制图为开发简单、低成本的技术提供了关键基础，这些技术增加了自然氮的衰减，从而改善了水质。这项工作的更广泛影响包括广泛的教育内容、公众宣传和技术转让的潜力。研究活动直接纳入学术课程，调查人员将指导高中生和本科生，培训研究生，并为传统上代表性不足的群体提供机会。这项工作在恢复水质方面取得的技术进步将传播给县、州和联邦各级的资源管理人员。总体而言，这一努力有助于加强对水产资源的管理。

AbstractTobias et al.?Collaborative Research: Linking hydrogeomorphology and denitrification in the tidal freshwater region of coastal stream?In recent decades, changes in land use and increasing population density have accelerated the delivery rates of nutrients (particularly nitrogen) from terrestrial sources to aquatic biomes. Humans now contribute more reactive nitrogen (N) to the hydro- and biospheres than all other natural N sources combined. Aquatic habitats have in turn responded with nuisance algal blooms, changes in species composition, impacts on fin and shellfish resources, and deleterious economic consequences. As streams and rivers trend closer towards nitrogen saturation, increasing amounts of nitrogen pollution are exported to the coastal margins where it promotes expanded severity and duration of hypoxic events. An understanding of the fate and transport of N through the entire aquatic continuum (e.g. streams, rivers and estuaries) is necessary for identifying zones that are particularly susceptible to N inputs, and those that act as hot spots for N removal. Knowledge of the hydrologic and chemical mechanisms controlling N reactivity provides the foundation for guiding nutrient management strategies and for enhancing the natural capacity of these environments to attenuate N loads. Measurement of denitrification, the only mechanism that represents absolute attenuation of nitrogen, has been examined across a wide range of aquatic ecotypes. However, one particular segment of the aquatic continuum, tidal freshwater rivers and streams, has generally escaped inquiry. Connecting upland streams and rivers to estuaries, we suggest that tidal freshwater streams possess unique hydrology, geomorphology, and chemical reactivity that optimize for N removal relative to any other component of the aquatic continuum. Further, we propose that enhanced N removal can be generated in non tidal systems simply by inducing a quasi-tidal hydrologic regime (i.e. by generating a rhythmic rise and fall in water level). Investigators propose to combine extensive hydro-chemical monitoring efforts in Coastal Plain streams in the Southeastern U.S. with a unique series of chemical tracer studies, and stream modeling. All work is to be conducted in situ under natural and hydrologically-manipulated conditions. Tidal streams are dominant aquatic features of the Southeastern US, and the proposed work will help to determine the extent to which they are a hotspot for N removal on broad geographic scales.The research represents a federal-academic partnership that will provide a better understanding of how nutrient loading in watersheds translates into ecosystem response along continental margins. Work of this nature is essential for improving predictions of habitat response to human perturbation and/or restoration effects, assessing resiliency of aquatic habitats, refining regulatory targets for nutrient loading. The mechanistic picture of how hydrology and chemistry interact to regulate N processing provides the critical foundation for developing simple low-cost technologies that enchance natural N attenuation and thereby improve water quality. Broader impacts of the work include extensive educational components, public outreach, and the potential for technology transfer. Research activities are integrated directly into academic curricula, investigators will mentor high school and undergraduate students, train graduate students, and provide opportunities for traditionally underrepresented groups. Technological advancements in water quality restoration resulting from this work will be disseminated to resource managers at the county, state, and federal levels. In total this effort facilitates enhanced stewardship of aquatic resources.