Ghosts of landuse past: legacy effects of milldams for riparian nitrogen (N) processing and water quality functions
Ghosts of landuse past: legacy effects of milldams for riparian nitrogen (N) processing and water quality functions
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DOI：
10.1088/1748-9326/abd9f5
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发表时间：
2021-03-01
影响因子：
6.7
通讯作者：
Trammell，Tara L. E.
中科院分区：
文献类型：
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作者：
Inamdar，Shreeram;Peipoch，Marc;Trammell，Tara L. E.
米尔达姆及其遗产对河流演变和地貌有着重大影响。然而，很少有人知道他们对河岸带水文，地球化学和水质的影响。在这里，我们讨论了现有的和违反milldams对河岸氮（N）处理的潜在影响，通过多个相互竞争的假设和观察互补的研究。竞争假说的特点河岸带过程，删除（汇）或释放（源）N。提高地下水位和减少土壤条件上游的milldams表明，河岸带以上的大坝可能是热点的氮去除通过反硝化和植物氮的吸收。另一方面，大坝拆除和随后的流和河岸地下水位下降导致排水，氧化土壤，这可能会增加土壤硝化作用和减少河岸植物吸收，由于地下水绕过根区。大坝拆除是否会导致河岸地下水中N的净增加或减少尚不清楚，需要进行调查。虽然硝化作用，反硝化作用和植物氮素吸收通常在河岸研究中受到最多的关注，其他N循环过程，如异化硝酸盐还原为铵（DNRA）需要考虑。我们还提出了一个新的概念河岸不连续体，突出了水文和地球化学的不连续性引入河岸带的人为结构，如milldams。理解和量化如何milldams和类似的结构影响河岸带的净源或汇的行为是迫切需要的指导流域管理的做法和明智的决策与大坝拆除。
Milldams and their legacies have significantly influenced fluvial processes and geomorphology. However, less is known about their effects on riparian zone hydrology, biogeochemistry, and water quality. Here, we discuss the potential effects of existing and breached milldams on riparian nitrogen (N) processing through multiple competing hypotheses and observations from complementary studies. Competing hypotheses characterize riparian zone processes that remove (sink) or release (source) N. Elevated groundwater levels and reducing soil conditions upstream of milldams suggest that riparian zones above dams could be hotspots for N removal via denitrification and plant N uptake. On the other hand, dam removals and subsequent drops in stream and riparian groundwater levels result in drained, oxic soils which could increase soil nitrification and decrease riparian plant uptake due to groundwater bypassing the root zone. Whether dam removals would result in a net increase or decrease of N in riparian groundwaters is unknown and needs to be investigated. While nitrification, denitrification, and plant N uptake have typically received the most attention in riparian studies, other N cycle processes such as dissimilatory nitrate reduction to ammonium (DNRA) need to be considered. We also propose a novel concept of riparian discontinuum, which highlights the hydrologic and biogeochemical discontinuities introduced in riparian zones by anthropogenic structures such as milldams. Understanding and quantifying how milldams and similar structures influence the net source or sink behavior of riparian zones is urgently needed for guiding watershed management practices and for informed decision making with regard to dam removals.