title: Nitrogen sink in a small forested watershed of subtropical China.
abstract: Global nitrogen (N) emission and deposition have been increased rapidly due to massive mobilization of N which may have long-reaching impacts on ecosystems. Many agricultural and forest ecosystems have been identified as secondary N sources. In the present study, the input-output budget of inorganic N in a small forested watershed of subtropical China was investigated. Inorganic N wet deposition and discharge by stream water were monitored from March, 2007 to February, 2009. The concentrations and fluxes of inorganic N in wet precipitation and stream water and net retention of N were calculated. Global N input by dry deposition and biological fixation and N output by denitrification for forested watersheds elsewhere were reported as references to evaluate whether the studied forested watershed is a source or a sink for N. The results show that the inorganic N output by the stream water is mainly caused by NO3(-)-N even though the input is dominated by NH4(+)-N. The mean flux of inorganic N input by wet precipitation and output by stream water is 1.672 and 0.537 g N/(m2 x yr), respectively, which indicates that most of inorganic N input is retained in the forested watershed. Net retention of inorganic N reaches 1.135 g N/(m2 x yr) considering wet precipitation as the main input and stream water as the main output. If N input by dry deposition and biological fixation and output by denitrification are taken into account, this subtropical forested watershed currently acts as a considerable sink for N, with a net sink ranging from 1.309 to 1.913 g N/(m2 x yr) which may enhance carbon sequestration of the terrestrial ecosystem.
authors.affiliation: State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China. Imhuang@issas.ac.cn
authors.forename: Laiming
authors.initials: L
authors.lastname: Huang
authors.forename: Jinling
authors.initials: J
authors.lastname: Yang
authors.forename: Ganlin
authors.initials: G
authors.lastname: Zhang
mesh_terms: D002681:China; D017753:Ecosystem; D004784:Environmental Monitoring / Q000379:methods; D009584:Nitrogen / Q000378:metabolism*; D012621:Seasons; D014197:Trees / Q000378:metabolism*; D014329:Tropical Climate; D014872:Water Movements; D014881:Water Supply
chemical_list: D009584:Nitrogen