title: Sources and fate of high levels of ammonium in surface water and shallow groundwater of the Jianghan Plain, Central China.
abstract: High levels of ammonium from anthropogenic sources threaten the quality of surface waters and groundwaters in some areas worldwide, but elevated ammonium levels of natural sources also have been identified. High levels of ammonium have been detected in both surface water and shallow groundwater of the Jianghan Plain, an alluvial plain of the Yangtze River. This study used N isotopes coupled with ancillary chemistry to identify ammonium in this region. Ammonium in the Tongshun River (up to 10.25 mg L-1) showed a sharp accumulation in the upstream and gradual attenuation in the downstream. The δ15N values of ammonium in the TSR were high and ranged narrowly from +12.5 to +15.4‰, suggesting an anthropogenic source that was septic effluent from industrial waste discharge. Sorption and nitrification were likely to respectively serve as the principal processes contributing to ammonium attenuation in different reaches of the downstream TSR. In shallow groundwater, high levels of ammonium (up to 14.10 mg L-1) occurred in a reducing environment. The narrow δ15N variation with low values (+2.3 to +4.5‰) in the lower aquifer suggested a natural source that was organic N mineralization. The δ15N values in the shallow aquitard exhibited a wide range from -1.8 to +9.4‰, owing to various sources. Two types of water in the shallow aquitard could be identified: (1) type-1 water with relatively longer residence time was similar to those in the aquifer where ammonium was mainly sourced from organic N mineralization; (2) type-2 water with shorter residence time was jointly affected by surface input, chemical attenuation and mineralization of organic N. The aquitard prevents prompt ammonium exchange between the surface and aquifer, and the shallower part of the aquitard provides a sufficient reaction time and an active reaction rate for ammonium removal.
authors.affiliation: School of Environmental Studies, China University of Geosciences, Lumo Road 388, Wuhan 430074, China. mateng@cug.edu.cn and State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Lumo Road 388, Wuhan 430074, China.
authors.forename: Yao
authors.initials: Y
authors.lastname: Du
authors.affiliation: School of Environmental Studies, China University of Geosciences, Lumo Road 388, Wuhan 430074, China. mateng@cug.edu.cn and State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Lumo Road 388, Wuhan 430074, China.
authors.forename: Teng
authors.identifier: http://orcid.org/0000-0003-2827-9579
authors.initials: T
authors.lastname: Ma
authors.affiliation: Geological Survey, China University of Geosciences, Lumo Road 388, Wuhan 430074, China. yamin.deng@cug.edu.cn and State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Lumo Road 388, Wuhan 430074, China.
authors.forename: Yamin
authors.initials: Y
authors.lastname: Deng
authors.affiliation: School of Environmental Studies, China University of Geosciences, Lumo Road 388, Wuhan 430074, China. mateng@cug.edu.cn and State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Lumo Road 388, Wuhan 430074, China.
authors.forename: Shuai
authors.initials: S
authors.lastname: Shen
authors.affiliation: Geological Survey, China University of Geosciences, Lumo Road 388, Wuhan 430074, China. yamin.deng@cug.edu.cn and State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Lumo Road 388, Wuhan 430074, China.
authors.forename: Zongjie
authors.initials: Z
authors.lastname: Lu
mesh_terms: D000327:Adsorption; D064751:Ammonium Compounds / Q000032:analysis*; D002681:China; D004784:Environmental Monitoring; D060587:Groundwater / Q000032:analysis; D058465:Nitrification; D045483:Rivers / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D064751:Ammonium Compounds; D014874:Water Pollutants, Chemical