[Temporal and spatial variation of non-point source nitrogen in surface water in urban agricultural region of Shanghai].

To know the temporal and spatial variation characteristics of non-point source nitrogen in surface water in urban agricultural region, and reveal the effect of non-point source nitrogen pollution on the quality of surface water, the contents of total nitrogen and inorganic nitrogen species in surface water were continuously monitored in Orchard Village, Nanhui District, Shanghai. The results were obtained as follows: (1) Spatial distribution of nitrogen in surface water is affected by hydrological periods and land use type. Mass concentration of nitrate nitrogen (NN) is high and that of ammonium nitrogen (AN) is low in surface water affected by the orchard, and the discrepancy of nitrogen concentration is high in wet season and low in dry season. Mass concentrations of NN and AN in surface water affected by residential region and factories show little difference, and the discrepancy of nitrogen concentration is high both in wet season and in dry season. (2) Winter and summer monsoons may affect the spatial distribution of nitrogen in surface water in the studied area. (3) Spatial variation of total nitrogen (TN), NN and AN is the highest in spring rain period, and it is higher in plum rain period and winter brief rain period than that in autumn rain period and summer brief rain period. Nitrite nitrogen (SNN) shows contrary spatial variation. (4) Dissolved organic nitrogen (DON, mass fraction in TN is 76.1%) is the main species in surface water in orchard region in May, while the dissolved inorganic nitrogen (DIN, mass fraction in TN is 83.2%) in other months. (5) The temporal variation of NN in orchard region is higher than that in residential region, while that of AN and TN in residential region is higher than that in orchard region.