降雨过程中香溪河流域非点源氮素入库特征研究

在香溪河流域主要支流开展了典型降雨事件过程中的水质水量同步监测,采用数字滤波法得到的基流指数分割了次降雨中的直接径流和基流,并用流量加权平均法估算了基流和直接径流中的氮素浓度,估算了降雨径流过程中点源和非点源氮素的入库(香溪河库湾)变化特征。结果表明:氮素浓度与流量的动态变化趋势基本一致,在降雨初期径流冲刷效应使浓度升高,在流量峰值到达的同时出现浓度最大值,之后随流量的减小而减小,并逐步趋于稳定;各形态氮素直接径流的浓度均大于基流,输出负荷以非点源为主,所占比例均达到70%以上,负荷贡献率表现为:TN>DTN>NO3--N>NH4+-N,TN的输出以DTN为主,DTN的输出以NO3--N为主;氮素输出负荷与径流量存在显著的相关性,TN、DTN、NO3--N、NH4+-N输出负荷与径流量的相关系数R值分别为0.93、0.95、0.98、0.88。有效控制农业非点源氮素输出是防治香溪河流域水体富营养化的关键。

Characteristics of Non-point Source Nitrogen Pollution Load in Xiangxi Basin during Raining

Water flow capacity and its quality were monitored synchronously at chief tributaries of Xiangxi River in Three Gorges Reservoir during typical raining.Surface flow and baseflow of rains were divided by use of baseflow index resulted from digital filter method.Mean nitrogen concentrations of direct surface flow and baseflow were estimated with weighted average method,and variation of nitrogen output from point source and non-point source during rains was analyzed.It indicated that the flow rate showed the same variation tendency of nitrogen concentration,the concentration rose at the beginning raining root in initial ground surface flushing and peak occurred at the same time as the flow peaks,then decreased with flow and finally kept in steady state.Various species of nitrogen concentrations all showed direct surface flow higher than baseflow.Non-point source pollution is the dominant output load,with load ratio all over 70%,and the contribution rate of load ranked from high to low as TN,DTN,NO3--N,NH4+-N,TN output mainly by DTN,DTN mainly by NO3--N.Runoff volume has prominent correlation with nitrogen output load,TN,DTN,NO3--N,NH4+-N correlation of load and flow are 0.93,095,0.98,0.88.The effective control of agricultural non-point source is the key to combat eutrophication in Xiangxi Basin.