重庆典型地区大气湿沉降氮的时空变化

验连续3a采集雨样研究了重庆市郊区和林区大气湿沉降氮的时空变化.结果表明,重庆市近郊区、远郊区和林区3个采样点雨水总氮浓度范围为(3.94±0.50)～(4.56±1.01)mg L-1,平均(4.27±0.73)mg L-1.NH+4-N、NO-3-N和DON占TN百分比例分别为44.9%、27.4%和27.5%.降雨中NH+4-N对氮沉降量的贡献率最大.在时间尺度上,不同季节降雨中氮浓度呈现明显的季节性差异,以冬季最高,依次是夏季、春季和秋季.在空间分布上,近郊区、远郊区和林区的TN平均浓度分别为4.56 mg L-1、4.32 mg L-1和3.94 mg L-1,从近郊区到林区有逐渐降低的趋势.降雨中的NH+4-N、NO-3-N、DON和TN浓度与降雨量无显著相关性.但是,降雨量与氮沉降量呈显著正相关.大气氮湿沉降时空差异与降雨量和氮排放直接相关.重庆市随降雨到达地面的氮沉降量较高,远远超过了水体负荷的临界值,可能对三峡库区的水资源产生不利影响.

variation in wet deposition of nitrogen from atmosphere in typical areas of Chongqing

The present experiment was carried out to investigate spatio-temporal changes in wet deposition of nitrogen from atmosphere in Chongqing area. Rainfall in successive three years was collected from three test sites, including a forestry site and two urban sites near and far from city, and analyzed for variable nitrogen concentrations. Total nitrogen (TN) in rainfall ranged from (3.94±0.50) mg L~(-1) to (4.56±1.01) mg L~(-1),averaged (4.27±0.73) mg L~(-1). NH_4~+-N accounted for 44.9%, NO_3~--N for 27.4% and DON (dissolved organic nitrogen) for 27.5% of TN in rainfall, respectively, indicating largest contribution of NH_4~+-N to wet deposition of nitrogen from atmosphere. The concentrations of nitrogen in rainfall varied seasonally, I.e. Winter > summer > spring and autumn. Nitrogen deposition in rainfall tended to decrease from the urban area near the city to forestry site far from city. TN concentrations in rainfall were 4.56 mg L~(-1)(urban area near the city), 4.32 mg L~(-1)(urban area far from city) and 3.94 mg L~(-1)(forestry area), respectively. Even though there were no correlations between nitrogen concentrations (NH_4~+-N、NO_3~--N、DON and TN) in rainfall and the amount of precipitation, wet deposition of nitrogen from atmosphere were positively correlated to the amount of rainfall. The amount of nitrogen deposition from rainfall in Chongqing, which was higher than critical index of nitrogen load in water and probably harmful to water resources in Three Gorge′s Area, varied spatio-temporally due to ground nitrogen emission and the amount of rainfall.