title: Assessment of the sources and transformations of nitrogen in a plain river network region using a stable isotope approach.
abstract: The great spatial and temporal variability in hydrological conditions and nitrogen (N) processing introduces large uncertainties to the identification of N sources and quantifying N cycles in plain river network regions. By combining isotopic data with chemical and hydrologic measurements, we determined the relative importance of N sources and biogeochemical N processes in the Taige River in the East Plain Region of China. The river was polluted more seriously by anthropogenic inputs in winter than in summer. Manure and urban sewage effluent were the main nitrate (NO3-) sources, with the nitrification of N-containing organic materials serving as another important source of NO3-. In the downstream, with minor variations in hydrological conditions, nitrification played a more important role than assimilation for the decreasing ammonium (NH4+-N) concentrations. The N isotopic enrichment factors (ε) during NH4+ utilization ranged from -13.88‰ in March to -29.00‰ in July. The ratio of the increase in δ18O and δ15N of river NO3- in the downstream was 1.04 in January and 0.92 in March. This ratio indicated that NO3- assimilation by phytoplankton was responsible for the increasing δ15N and δ18O values of NO3- in winter. The relationships between δ15N of particulate organic nitrogen and isotopic compositions of dissolved inorganic nitrogen indicated that the phytoplankton in the Taige River probably utilized NH4+ preferentially and mainly in summer, while in winter, NO3- assimilation by phytoplankton was dominant.
authors: School of Environment, Beijing Normal University, Beijing 100875, China E-mail: dingjingtao@163.com. Electronic address: dingjingtao@163.com.
authors: Jingtao
authors: J
authors: Ding
authors: Chinese Research Academy of Environmental Sciences, Beijing 100012, China. Electronic address: xibeidou@263.net.
authors: Beidou
authors: B
authors: Xi
authors: Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
authors: Qigong
authors: Q
authors: Xu
authors: Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
authors: Jing
authors: J
authors: Su
authors: Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
authors: Shouliang
authors: S
authors: Huo
authors: Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
authors: Hongliang
authors: H
authors: Liu
authors: Changzhou Environmental Monitoring Center, Jiangsu 213001, China.
authors: Yijun
authors: Y
authors: Yu
authors: Changzhou Environmental Monitoring Center, Jiangsu 213001, China.
authors: Yanbo
authors: Y
authors: Zhang
mesh_terms: D064751:Ammonium Compounds / Q000032:analysis*; D002681:China; D004784:Environmental Monitoring; D009566:Nitrates / Q000032:analysis*; D009587:Nitrogen Isotopes / Q000032:analysis; D052638:Particulate Matter / Q000032:analysis*; D010839:Phytoplankton / Q000378:metabolism; D045483:Rivers / Q000737:chemistry*; D012621:Seasons; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D064751:Ammonium Compounds; D009566:Nitrates; D009587:Nitrogen Isotopes; D052638:Particulate Matter; D014874:Water Pollutants, Chemical
keywords: Assimilation; Nitrate; Nitrification; Plain river network region; Stable isotopes