Oak Ridge Institute for Science and Education (ORISE) Research Participation Program, Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, OH, USA.
Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, OH, USA.
J Environ Manage. 2024 Nov;370:122500. doi: 10.1016/j.jenvman.2024.122500. Epub 2024 Sep 19.
Connections between agricultural runoff and excess nitrogen in the Upper Mississippi River Basin are well-documented, as is the potential role of constructed wetlands in mitigating this surplus nitrogen. However, limited knowledge exists about the "best" placement of these wetlands for downstream nitrogen reductions within a whole watershed context as well as how far downstream these benefits are realized. In this study, we simulate the cumulative impacts of diverse wetland restoration scenarios on downstream nitrate reductions in different subbasins of the Raccoon River Watershed, Iowa, USA, and spatially trace their relative effects downstream. Our simulated results underscore previous work demonstrating that the total area of wetlands and the wetland-catchment-to-wetland area ratio are both significant factors for determining the nitrate load reduction benefits of wetlands at subbasin scales. Simulated wetland conservation scenarios resulted in nitrate load decreases ranging from 7.5 to 43.2% of our baseline model loads. However, we found these wetland-mediated nitrate reduction benefits are quickly attenuated downstream: load reductions were <1% at the watershed outlet across all model scenarios, despite the magnitude of the subbasin-scale nitrate decreases. The relatively rapid attenuation of wetland effects is largely due to downstream nitrate load contributions from untreated subbasins. However, higher subbasin-scale nitrate reductions from wetland-based conservation practices resulted in longer downstream distances prior to attenuation. This study highlights the importance of considering the spatial location of constructed or restored wetlands relative to the area within the watershed where nitrogen reductions are most needed.
农业径流和密西西比河流域上流域过量氮之间的联系是有据可查的，人工湿地在减轻这种过剩氮方面的潜在作用也是如此。然而，对于在整个流域范围内这些湿地对于下游氮减少的“最佳”位置，以及这些好处在多远的下游实现，人们的了解有限。在这项研究中，我们模拟了不同湿地恢复情景对美国爱荷华州浣熊河流域不同子流域下游硝酸盐减少的累积影响，并在空间上追踪它们的下游相对影响。我们的模拟结果强调了先前的工作，表明湿地总面积和湿地流域比湿地面积比都是确定湿地在子流域尺度上减少硝酸盐负荷的重要因素。模拟的湿地保护情景导致硝酸盐负荷减少了我们基线模型负荷的 7.5%至 43.2%。然而，我们发现这些湿地介导的硝酸盐减少效益在下游迅速减弱：尽管子流域尺度上硝酸盐减少的幅度很大，但在所有模型情景下，在流域出口处的负荷减少<1%。湿地效应的相对迅速衰减主要是由于未处理的子流域的下游硝酸盐负荷贡献。然而，来自基于湿地的保护实践的更高的子流域尺度硝酸盐减少导致在衰减之前的下游距离更长。本研究强调了相对于流域内最需要减少氮的区域，考虑人工或恢复湿地的空间位置的重要性。
