Where a river slows: investigating the oscillic freshwater zone

当河流入海时，会出现一个令人惊讶的、复杂的、人们知之甚少的“振荡淡水带”，在这里，河水可能会随着潮水而变慢、停止，甚至逆转方向，但却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湍急的河流或缓慢流动的湖泊，也可以是两者的混合体。尽管人们对这些行为知之甚少，但任何变化都会影响河流向海洋输送淡水和污染物的速度。河流污染物径流是一个（国际）国家问题，严重影响河流和海洋生态系统以及渔业的健康。振荡带可能已经在河流危害海岸之前清除了一些污染物，通过减缓河流的流动，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以及所涉及的具体过程尚不清楚。为了确保这些免费的、自然的好处不会因为河流管理、降雨或海平面的变化而丧失，我们需要更好地了解振荡带是如何工作的。这个项目是第一个定义和研究振荡带作为河流的一个重要部分，不适合以前的快慢河流分类。本研究将回答三个问题：1)快流和慢流如何交替定义振荡带？2)这个区域对到达海岸的氮污染物有什么影响？3)该地区对海平面、降雨和河流管理的变化有多敏感？该项目包括对两条德克萨斯河振荡带的详细实地研究。这些真实世界的见解将与计算机模型相结合，以更好地理解动态物理化学联系，并预测人类和自然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进行全球共享，该门户网站托管振荡区物理/化学的动画模拟。该门户网站将实时展示美国西部墨西哥湾沿岸所有河流的震荡带及其与墨西哥湾的联系。该门户网站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，该项目将与与实地地点相关的当地水质委员会合作，寻求直接告知真正的河流管理政策，并将与国家河口研究保护区合作，加强小学及以上关于河海联系的教育材料。

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.