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Lateral hyporheic exchange throughout the Mississippi River network

机译：整个密西西比河网的横向水交换

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摘要

River water circulates vertically through the river bed and laterally through bank sediments. This hyporheic exchange brings river water into contact with microbes in the adjacent sediments, otherwise known as the hyporheic exchange zone. As such, hyporheic zones act as hotspots for the biogeochemical cycling of carbon, metals and nutrients in rivers, and can, for example, influence the export of nitrogen todownstreamecosystems. Here,we calculate the extent and duration of lateral hyporheic exchange throughout the Mississippi River network, using a physics-based numerical model that takes into account the distribution of groundwater baseflow, river discharge, alluvium permeability and river morphology. Wefindthat in our simulations, lateral exchange occurs throughout the network: practically all of the river water that reaches the mouth of the Mississippi River network has circulated through the lateral hyporheic zone. River water residence time in the hyporheic zone ranges from less than an hour in headwaters to over a month in larger channels. Comparison of the residence times that we derive to a previously reportedresidence time threshold for denitrification suggests that around one quarter of the lateral hyporheic zones in theMississippi River network favour denitrification, and thus nitrogen loss. Given that river water can circulate many times through the river bank before reaching the river mouth, and can undergo vertical exchange with the river bed, we suggest that our estimates serve as a lower limit for potential nitrogen loss.
机译：河水在河床中垂直循环，在河岸沉积物中横向流动。这种交换性交换使河水与相邻沉积物中的微生物接触，也称为交换性交换带。因此，流变带是河流中碳，金属和养分的生物地球化学循环的热点，并可能例如影响氮向下游生态系统的出口。在这里，我们使用基于物理的数值模型来计算整个密西西比河网络的横向低渗交换的程度和持续时间，该模型考虑了地下水基流，河流流量，冲积渗透率和河流形态的分布。我们发现，在我们的模拟中，横向交换发生在整个网络中：实际上，到达密西西比河网口的所有河水都已通过横向次流带循环。上游水域的河水停留时间从上游的不到一小时到大型河道的一个月以上不等。将我们得出的停留时间与先前报道的反硝化停留时间阈值进行比较，发现密西西比河网络中大约四分之一的侧向低渗带有利于反硝化，因此有利于氮的流失。鉴于河水在到达河口之前可以通过河岸循环多次，并且可以与河床进行垂直交换，因此我们建议将我们的估算值作为潜在氮损失的下限。

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