Abstract: Based on the monthly groundwater sampling and measurements, the seasonal variations and spatial distributions of nitrogen in ground phreatic water were analyzed in the hilly valley plain of Changle River Watershed, Zhejiang Province, China. The area occupation ratios of different land use patterns were extracted in the areas of different radius (50, 100, 250, 500, 1 000, 1 250, 1 500 m) around each sampling site to investigate the correlation within land use patterns and the corresponding groundwater nitrogen concentration. It was shown that the average concentrations of nitrate nitrogen (NO3--N) and total N (TN) were (1.326±0.618) and (2.717±1.614) mg·L^-1, respectively. The temporal and spatial distributions of TN concentration in the plain groundwater showed strong consistency with NO3--N. Both TN and NO3--N concentrations were higher in wet season than those in dry season, and they were always higher under the land use pattern of gardens (vegetables and seedlings) and cultivated lands (rice and rape) than those in others. The average concentration of NH₃-N in the plain groundwater was (0.434±0.158) mg·L^-1, which was only about 16% of the TN concentration. NH₃-N concentrations in groundwater were lower in the wet season than those in the dry season, and it showed an increasing trend nearby the water body (river and pond).

Key words: hilly valley plain, intensive agriculture, ground phreatic water, spatial and temporal distributions, land use pattern