Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University, SE-39182, Kalmar, Sweden; Machinery Laboratory, Vattenfall R&D, 81470, Älvkarleby, Sweden.
Department of Environmental and Biosciences, School of Business, Innovation and Sustainability, Halmstad University, Box 823, 301 18 Halmstad, Sweden; Department of Ecology and Genetics, Uppsala University, Box 256, 751 05 Uppsala, Sweden.
Chemosphere. 2024 Jul;359:142284. doi: 10.1016/j.chemosphere.2024.142284. Epub 2024 May 6.
Wetland management maintains nitrogen (N) removal capacity in mature and overgrown constructed wetlands (CWs). We evaluated whether CW management by macrophyte harvesting, and subsequent installation of woodchips-based floating beds (WFBs) planted with Glyceria maxima and Filipendula ulmaria improved N removal. In sixteen heavily overgrown experimental CWs, we applied four treatments: i) only macrophyte harvesting, ii) 5% of the harvested-CW surface covered with WFBs, iii) 20% WFBs cover, and iv) a control treatment (heavily overgrown). N removal was determined in all wetlands at nine occasions. Plant biomass accrual, N assimilation, and denitrification genes nirS, nirK, nosZI and nosZII on plant roots and woodchips from WFBs were estimated. Macrophyte harvesting improved N removal of heavily overgrown CWs, whereas subsequent WFB installation only sometimes improved N removal. Mean N removal efficiencies (± standard deviation) overall were 41 ± 15 %, 45 ± 20 %, 46 ± 16 % and 27 ± 8.3 % for treatments i to iv, respectively. Relative biomass production, root length and root surface area for G.maxima (mean ± standard deviation: 234 ± 114 %, 40 ± 6.5 cm, 6308 ± 1059 cmg, respectively) were higher than those for F. ulmaria (63 ± 86 %, 28 ± 12 cm, 3131 ± 535 cmg, respectively) whereas biomass N assimilation was higher for F. ulmaria (1.8 ± 0.9 gNm of WFB) than for G. maxima (1.3 ± 0.5 gNm of WFB). Denitrification gene abundance was higher on plant roots than on woodchips while G. maxima hosted higher root denitrification gene abundance than F. ulmaria. We conclude that macrophyte harvesting improves N removal in heavily overgrown CWs. WFBs installation has the potential to support plant growth and denitrification in surface-flow constructed wetlands. Further studies need to evaluate the long-term effects of macrophyte harvesting and WFB installation on N removal in CWs.
湿地管理维持成熟和过度生长的人工湿地（CWs）的氮（N）去除能力。我们评估了通过收割大型植物和随后安装基于木屑的浮床（WFB）来管理 CW 的方法，这些浮床种植了高羊茅和欧洲菘蓝，以改善 N 去除效果。在十六个过度生长的实验性 CW 中，我们应用了四种处理方法：i）仅收割大型植物，ii）5%的收割-CW 表面覆盖 WFB，iii）20%的 WFB 覆盖，iv）对照处理（过度生长）。在所有湿地进行了九次 N 去除测定。估计了植物生物量积累、植物根系和 WFB 木屑中的 N 同化以及反硝化基因 nirS、nirK、nosZI 和 nosZII。大型植物收割改善了过度生长的 CW 的 N 去除效果，而随后安装 WFB 则只能在某些情况下改善 N 去除效果。总体而言，处理 i 至 iv 的 N 去除效率平均值（±标准偏差）分别为 41±15%、45±20%、46±16%和 27±8.3%。高羊茅（平均值±标准偏差：234±114%、40±6.5cm、6308±1059 cmg）的相对生物量产生、根长和根表面积均高于欧洲菘蓝（63±86%、28±12cm、3131±535 cmg），而欧洲菘蓝的生物质 N 同化量（1.8±0.9 gNm 的 WFB）高于高羊茅（1.3±0.5 gNm 的 WFB）。与木屑相比，植物根系上的反硝化基因丰度更高，而高羊茅上的根反硝化基因丰度高于欧洲菘蓝。我们得出结论，大型植物收割可提高过度生长的 CW 的 N 去除效果。WFB 的安装有可能支持表面流人工湿地中的植物生长和反硝化作用。需要进一步研究评估大型植物收割和 WFB 安装对 CW 中 N 去除的长期影响。
