To investigate the spatiotemporal variations of the nitrogen pollution in the tableland-gully region of the Loess Plateau,the surface water and groundwater in the Heihe watershed( tributary of the Jing River catchment) have been sampled in the dry and flood seasons for the period of 2013—2014to determine the concentration of NO_3~--N and NH+4-N. The major water type is Na +K-Cl-SO4 during the dry seasons and Ca-Mg-HCO3 during the flood seasons. Na+is the major cation for both dry and flood season,while the ...