N‐loads from subsurface, drains, and groundwater‐fed surface (bypass) flows via two riparian zones (crop field and wetland) to a second order stream were investigated by sampling of shallow and deep groundwater on both sides and monthly measurements of bypass flows from springs, drains, and stream including water quality (nitrate). A push‐pull test in the crop field gave a first‐order denitrification rate (0.23 day^–1). Reactive transport modeling evaluated observations of water chemistry and denitrification processes in the groundwater below the crop field showing that nitrate was completely removed by denitrification with pyrite in the aquifer (model rates of 0.6–2.5 mmol NO₃ L⁻¹ yr⁻¹). A drain in the crop field routed ∼10% (bypass) of the regional groundwater inflow to the stream. Buffer efficiency was high at 90%. The wetland on the other side of the stream hosts several locations of nitrate‐rich bypass flow from springs, predominantly through a non‐maintained drainage system of drainpipes and ditches with bypass flow accounting for 59% of the regional flow input. Nitrate was completely removed in groundwater by denitrification with dissolved organic matter in shallow groundwater. The regional inflow and N load to the wetland is amongst the highest recorded and data shows that the N load to the stream is very high. The buffer efficiency ranged from 45% to 83% depending on if all bypass flows contributed to the stream or only the two with visible outflow. A conceptual model for nitrate removal efficiency as a function of Damköhler number and percent bypass flow is proposed.

中文翻译：

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氮气流：旁路流量和硝酸盐去除工艺的重要性

通过对两侧浅层和深层地下水进行采样并每月测量旁路流量，研究了从地下，排水沟和地下水供给的地表（旁路）流经两个河岸带（作物田和湿地）到二阶水流的N负荷。来自泉水，下水道和包括水质（硝酸盐）的溪流。作物田中的推拉试验得出一阶反硝化率（0.23天^–1）。反应性运输模型评估了作物田以下地下水中水化学和反硝化过程的观察结果，表明在含水层中通过黄铁矿的反硝化作用已完全去除了硝酸盐（模型速率为0.6–2.5 mmol NO ₃ L ^-1  yr ^-1）。作物田中的排水道将大约10％的区域地下水流入（旁路）。缓冲效率高达90％。溪流另一侧的湿地主要来自泉水，分布在硝酸盐丰富的旁路水流的多个位置，主要通过不维护的排水管和沟渠排水系统，旁路水流占区域流量输入的59％。通过溶解在浅层地下水中的有机物进行反硝化，可以完全去除地下水中的硝酸盐。记录到湿地的区域流入量和氮负荷是记录的最高值之​​一，数据表明，流中的氮负荷非常高。缓冲效率的范围从45％到83％，具体取决于是所有旁路流都促成该流，还是仅这两个具有可见的流出。