title: Temporal variation of nitrogen balance within constructed wetlands treating slightly polluted water using a stable nitrogen isotope experiment.
abstract: Slightly polluted water has become one of the main sources of nitrogen contaminants in recent years, for which constructed wetlands (CW) is a typical and efficient treatment. However, the knowledge about contribution of individual nitrogen removal pathways and nitrogen balance in constructed wetlands is still limited. In this study, a stable-isotope-addition experiment was performed in laboratory-scale constructed wetlands treating slightly polluted water to determine quantitative contribution of different pathways and temporal variation of nitrogen balance using Na(15)NO3 as tracer. Microbial conversion and substrate retention were found to be the dominant pathways in nitrogen removal contributing 24.4-79.9 and 8.9-70.7 %, respectively, while plant contributed only 4.6-11.1 % through direct assimilation but promoted the efficiency of other pathways. In addition, microbial conversion became the major way to remove N whereas nitrogen retained in substrate at first was gradually released to be utilized by microbes and plants over time. The findings indicated that N2 emission representing microbial conversion was not only the major but also permanent nitrogen removal process, thus keeping a high efficiency of microbial conversion is important for stable and efficient nitrogen removal in constructed wetlands.
authors.affiliation: State Key Laboratory of Pollutant Control and Resources Reuse, School of the Environment, Nanjing University, 163 Xianlin Avenue, Nanjing, 210023, People's Republic of China.
authors.forename: Wanguang
authors.initials: W
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Pollutant Control and Resources Reuse, School of the Environment, Nanjing University, 163 Xianlin Avenue, Nanjing, 210023, People's Republic of China.
authors.forename: Qiongye
authors.initials: Q
authors.lastname: Lei
authors.affiliation: State Key Laboratory of Pollutant Control and Resources Reuse, School of the Environment, Nanjing University, 163 Xianlin Avenue, Nanjing, 210023, People's Republic of China. zhkuili@nju.edu.cn.
authors.forename: Zhengkui
authors.initials: Z
authors.lastname: Li
authors.affiliation: State Key Laboratory of Pollutant Control and Resources Reuse, School of the Environment, Nanjing University, 163 Xianlin Avenue, Nanjing, 210023, People's Republic of China.
authors.forename: Huayang
authors.initials: H
authors.lastname: Han
mesh_terms: D001673:Biodegradation, Environmental; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes / Q000378:metabolism; D010944:Plants / Q000378:metabolism; D011849:Radioactive Tracers; D012988:Soil Microbiology; D014871:Water Microbiology; D014876:Water Pollution; D053833:Wetlands
chemical_list: D009587:Nitrogen Isotopes; D011849:Radioactive Tracers; D009584:Nitrogen
keywords: Constructed wetlands; Elodea nuttallii and Iris sibirica; N2 and N2O emission; Nitrogen balance; Stable isotope; Temporal variation