Eutrophication, harmful algal blooms, and human health impacts are critical environmental challenges resulting from excess nitrogen and phosphorus in surface waters. Yet we have limited information regarding how wetland characteristics mediate water quality across watershed scales. We developed a large, novel set of spatial variables characterizing hydrological flowpaths from wetlands to streams, that is, “wetland hydrological transport variables,” to explore how wetlands statistically explain the variability in total nitrogen (TN) and total phosphorus (TP) concentrations across the Upper Mississippi River Basin (UMRB) in the United States. We found that wetland flowpath variables improved landscape-to-aquatic nutrient multilinear regression models (from R² = 0.89 to 0.91 for TN; R² = 0.53 to 0.84 for TP) and provided insights into potential processes governing how wetlands influence watershed-scale TN and TP concentrations. Specifically, flowpath variables describing flow-attenuating environments, for example, subsurface transport compared to overland flowpaths, were related to lower TN and TP concentrations. Frequent hydrological connections from wetlands to streams were also linked to low TP concentrations, which likely suggests a nutrient source limitation in some areas of the UMRB. Consideration of wetland flowpaths could inform management and conservation activities designed to reduce nutrient export to downstream waters.

中文翻译：

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湿地流道调节密西西比河流域上游的氮和磷浓度

富营养化、有害藻华和人类健康影响是地表水中过量氮和磷造成的严重环境挑战。然而，关于湿地特征如何调节流域尺度的水质，我们的信息有限。我们开发了一组新颖的空间变量，描述从湿地到溪流的水文流动路径，即“湿地水文输送变量”，以探索湿地如何统计解释整个地区总氮（TN）和总磷（TP）浓度的变化。美国密西西比河流域上游 (UMRB)。我们发现湿地流径变量改善了景观到水生养分的多线性回归模型（ TN从R ^{2 = 0.89 到 0.91；} R²  = 0.53 至 0.84（对于 TP）），并提供了对湿地如何影响流域规模 TN 和 TP 浓度的潜在过程的见解。具体而言，描述流量衰减环境的流路变量（例如，与陆上流路相比的地下输送）与较低的总氮和总磷浓度相关。从湿地到溪流的频繁水文联系也与低总磷浓度有关，这可能表明 UMRB 某些地区的营养源有限。考虑湿地流道可以为旨在减少向下游水域的养分输出的管理和保护活动提供信息。