Saturated, Suffocated, and Salty: Human Legacies Produce Hot Spots of Nitrogen in Riparian Zones
Saturated, Suffocated, and Salty: Human Legacies Produce Hot Spots of Nitrogen in Riparian Zones
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DOI：
10.1029/2022jg007138
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发表时间：
2022-12
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通讯作者：
S. Inamdar;E. Peck;M. Peipoch;A. Gold;M. Sherman;Johanna Hripto;P. Groffman;T. Trammell;D. Merritts;K. Addy;Evan Lewis;R. Walter;J. Kan
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作者：
S. Inamdar;E. Peck;M. Peipoch;A. Gold;M. Sherman;Johanna Hripto;P. Groffman;T. Trammell;D. Merritts;K. Addy;Evan Lewis;R. Walter;J. Kan
人类活动遗留下来的环境污染的复合效应是显著的，但尚未得到很好的理解。在这里，我们表明，百年规模的遗产milldams和道路盐盐渍化的十年规模的遗产以意想不到的方式相互作用，在河岸带产生氮（N）的热点。在2年的时间内，对两个中大西洋（宾夕法尼亚州和特拉华州）2.4 m和4 m高的milldams上游的河岸地下水和河水浓度进行了采样。粘土和淤泥丰富的遗留沉积物具有低水力传导性，停滞和混合不良的水文条件，以及磨坊坝上游河岸沉积物中的持续缺氧，产生了独特的生态地球化学梯度，通过高地河岸边缘的反硝化作用去除硝酸盐，并在近流沉积物和地下水中积累铵氮。磨坊水坝上游河岸地下水铵氮浓度范围为0.006 - 30.6 mgN L−1，而土壤结合值为0.11-456 mg kg−1。我们属性的铵浓度升高氨化与抑制硝化和/或异化硝酸盐还原铵（DNRA）。来自道路盐的钠输入到河岸地下水（25- 1，504 mg L−1）可能会进一步提高DNRA和铵的产量，并将吸附的土壤铵-N转移到地下水中。这项研究表明，遗产的milldams和道路盐可能会削弱河岸带的N缓冲能力，需要考虑在河岸缓冲区评估，流域管理计划，大坝拆除的决定。考虑到水坝和其他屏障的广泛存在以及道路盐的普遍使用，这种协同作用的N污染的潜力是显着的。
The compounding effects of anthropogenic legacies for environmental pollution are significant, but not well understood. Here, we show that centennial‐scale legacies of milldams and decadal‐scale legacies of road salt salinization interact in unexpected ways to produce hot spots of nitrogen (N) in riparian zones. Riparian groundwater and stream water concentrations upstream of two mid‐Atlantic (Pennsylvania and Delaware) milldams, 2.4 and 4 m tall, were sampled over a 2 year period. Clay and silt‐rich legacy sediments with low hydraulic conductivity, stagnant and poorly mixed hydrologic conditions, and persistent hypoxia in riparian sediments upstream of milldams produced a unique biogeochemical gradient with nitrate removal via denitrification at the upland riparian edge and ammonium‐N accumulation in near‐stream sediments and groundwaters. Riparian groundwater ammonium‐N concentrations upstream of the milldams ranged from 0.006 to 30.6 mgN L−1 while soil‐bound values were 0.11–456 mg kg−1. We attribute the elevated ammonium concentrations to ammonification with suppression of nitrification and/or dissimilatory nitrate reduction to ammonium (DNRA). Sodium inputs to riparian groundwater (25–1,504 mg L−1) from road salts may further enhance DNRA and ammonium production and displace sorbed soil ammonium‐N into groundwaters. This study suggests that legacies of milldams and road salts may undercut the N buffering capacity of riparian zones and need to be considered in riparian buffer assessments, watershed management plans, and dam removal decisions. Given the widespread existence of dams and other barriers and the ubiquitous use of road salt, the potential for this synergistic N pollution is significant.