Abstract Diffuse pollution from agricultural drainage is a severe problem for water quality and it is a major reason for the failure to accomplish “good chemical status of surface waters” according to the Water Framework Directive and for the eutrophication of both freshwaters and coastal waters. Constructed wetlands were proposed as a suitable tool for removal of nitrogen from agricultural drainage in the early 1990s. Until now, the vast majority of constructed wetlands designed to treat tile drainage were free-surface constructed wetlands. In 2018, three experimental constructed wetlands with horizontal subsurface flow were built to treat tile drainage from 15.73 ha watershed. The wetlands have a surface area of 79, 90 and 98 m2 and were planted with Phalaris arundinacea and Glyceria maxima in parallel bands. The substrate in the first two wetlands is gravel (4–8 mm) mixed with birch woodchips (10: 1 volume ratio). In one of those wetlands, the water level is kept 10 cm above the surface, in the second one the water is kept below the surface. The third wetland has 20 cm layer of birch woodchips on top of gravel. The mean total nitrogen concentration eliminations during one-year period were 61.2%, 62.6% and 70.9% for wetlands 1, 2 and 3, respectively. The average load removals amounted to 0.516, 0.323 and 0.399 g N m−2 d−1 or 1885, 1180 and 1457 kg ha−1 yr−1 in wetlands 1, 2 and 3 respectively. The plant uptake and nitrogen sequestration in aboveground biomass contributed only marginally to the overall nitrogen removal. The results revealed that the selection of the best option depends on the fact whether concentration or load is taken as the most important parameter.

中文翻译：

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具有地下流的人工湿地去除瓷砖排水中的氮

摘要 农业排水的弥漫性污染是水质的一个严重问题，它是未能达到《水框架指令》规定的“地表水良好化学状态”以及淡水和沿海水域富营养化的主要原因。人工湿地在 1990 年代初期被提议作为从农业排水中去除氮的合适工具。到目前为止，绝大多数用于处理瓷砖排水的人工湿地都是自由表面人工湿地。2018 年，建设了三个具有水平地下流的实验性人工湿地，用于处理 15.73 公顷流域的瓦片排水。湿地的表面积分别为 79、90 和 98 平方米，并在平行带中种植了菖蒲和 Glyceria maxima。前两个湿地的基质是砾石（4-8 毫米）与桦木屑（体积比为 10:1）混合。在其中一个湿地中，水位保持在地表以上 10 厘米，在第二个湿地中，水位保持在地表以下。第三个湿地在砾石顶部有 20 厘米厚的桦木木片。湿地 1、2 和 3 一年期间的平均总氮浓度消除量分别为 61.2%、62.6% 和 70.9%。在湿地 1、2 和 3 中，平均负载移除量分别为 0.516、0.323 和 0.399 g N m-2 d-1 或 1885、1180 和 1457 kg ha-1 yr-1。地上生物量中的植物吸收和固氮对整体氮去除的贡献很小。