Where a river slows: investigating the oscillic freshwater zone

当河流接近大海时，有一个令人惊讶的、复杂的、鲜为人知的“震荡淡水区”，在那里，河流的流动可能会随着潮汐而减缓、停止甚至反向，但看不到一盎司的海水。在不同的时间，这个区域可以表现得像一条湍急的河流或缓慢流动的湖泊，或者两者的混合体。尽管人们对这些行为知之甚少，但任何变化都会影响河流将淡水和污染物输送到海洋的速度。河流污染物径流是一个(国际)全国性问题，严重影响河流和海洋生态系统和渔业的健康。Oscillic区可能已经在河流损害海岸之前消除了一些污染物，方法是减缓河流的流动速度，并在沿途实现更多的自然化学缓解。然而，这种情况发生的程度和涉及的具体过程尚不清楚。为了确保这些免费的自然利益不会因为河流管理、降雨或海平面的变化而丧失，我们需要更好地了解震荡带是如何工作的。该项目是第一个将震荡带作为河流的重要部分进行定义和调查的项目，不符合以前的快慢河流分类。这项研究将回答三个问题：1)快流和慢流的交替定义了一个震荡区？2)这个区对到达海岸的氮污染物有什么影响？3)该区域对海平面、降雨量和河流管理的变化有多敏感？该项目包括对德克萨斯州河流的两个震荡带进行详细的实地研究。这些现实世界的见解将与计算机模型相结合，以更好地了解动态的物理化学联系，并预测人类和自然的影响如何影响淡水和污染物向海岸的输送。这项研究将在一个公共门户网站上全球共享，该门户网站上托管着震荡带物理/化学的动画模拟。该门户将实时显示美国墨西哥湾西部所有河流的震荡带及其与墨西哥湾的连接。该门户还将提供一个更通用的工具，使任何人都可以探索和测试不同类型河流的振荡带动力学。为了进一步联系教育和管理，该项目将与当地与实地有关的水质委员会合作，寻求直接为真正的河流管理政策提供信息，并将与国家河口研究保护区合作，加强关于江海连接的小学和成人教育材料。

As rivers approach the sea there is surprising, complex, and poorly understood "oscillic freshwater zone" where the river flow may slow, stop, or even reverse direction with the tide, but not an ounce of seawater is seen. This zone can behave like a fast-flowing river or a slow-flowing lake or a mixture of the two, at different times. Although these behaviors are poorly understood, any variations will affect how fast the river transports freshwater and pollutants to the sea. Pollutant runoff from rivers is an (inter)national problem that significantly impacts the health of river and ocean ecosystems and fisheries. Oscillic zones likely already remove some pollutants from rivers before they harm the coast, by slowing their flow and enabling more natural chemical mitigation along the way. The degree to which this is occurring, however, and the specific processes involved are unknown. To ensure that these free, natural benefits are not lost due to changes in river management, rainfall, or sea level, we need to better understand how oscillic zones work. This project is the first to define and investigate the oscillic zone as an important section of a river that does not fit previous fast-or-slow river classifications. This research will answer three questions: 1) What alternation of fast and slow flows defines an oscillic zone? 2) What effect does this zone have on nitrogen pollutants reaching the coast? and 3) How sensitive is this zone to changes in sea level, rainfall, and river management? The project includes detailed field study of two Texas river' oscillic zones. These real-world insights will be combined with computer models to better understand dynamic physics-chemistry links and to predict how human and natural influences affect freshwater and pollutant delivery to the coast. This research will be globally shared on a public web portal hosting animated simulations of oscillic zone physics/chemistry. The portal will illustrate the oscillic zones of all the US western Gulf Coast rivers and their connections to the Gulf in real-time. The portal will also host a more general tool enabling anyone to explore and test oscillic zone dynamics for different types of rivers. To further connect to education and management, the project will work with the local water quality committee relevant to the field sites to seek to directly inform real river management policy and will enhance elementary school-and-up educational materials on river-sea connections, in partnership with a National Estuarine Research Reserve.