Enhancing nitrogen removal through macrophyte harvest and installation of woodchips-based floating beds in surface-flow constructed wetlands

Maidul I Choudhury; Josefin E Nilsson; Samuel Hylander; Marc Hauber; Per Magnus Ehde; Stefan E B Weisner; Antonia Liess

doi:10.1016/j.chemosphere.2024.142284

Enhancing nitrogen removal through macrophyte harvest and installation of woodchips-based floating beds in surface-flow constructed wetlands

Chemosphere. 2024 May 6:359:142284. doi: 10.1016/j.chemosphere.2024.142284. Online ahead of print.

Authors

Maidul I Choudhury¹, Josefin E Nilsson², Samuel Hylander³, Marc Hauber³, Per Magnus Ehde⁴, Stefan E B Weisner⁴, Antonia Liess⁵

Affiliations

¹ Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University, SE-39182, Kalmar, Sweden; Machinery Laboratory, Vattenfall R&D, 81470, Älvkarleby, Sweden.
² 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.
³ Centre for Ecology and Evolution in Microbial Model Systems, Linnaeus University, SE-39182, Kalmar, Sweden.
⁴ Department of Environmental and Biosciences, School of Business, Innovation and Sustainability, Halmstad University, Box 823, 301 18 Halmstad, Sweden.
⁵ Department of Environmental and Biosciences, School of Business, Innovation and Sustainability, Halmstad University, Box 823, 301 18 Halmstad, Sweden. Electronic address: antonia.liess@hh.se.

PMID: 38719124
DOI: 10.1016/j.chemosphere.2024.142284

Abstract

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 cm²g^-1, respectively) were higher than those for F. ulmaria (63 ± 86 %, 28 ± 12 cm, 3131 ± 535 cm²g^-1, respectively) whereas biomass N assimilation was higher for F. ulmaria (1.8 ± 0.9 gNm^-2 of WFB) than for G. maxima (1.3 ± 0.5 gNm^-2 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.

Keywords: Aquatic plants; Floating wetlands; Nitrogen uptake; Wetland biofilm; Wetland restoration.