红壤丘陵区小流域典型土地利用的面源氮磷输出特征

Output Characteristics of Nitrogen and Phosphorus from Non-Point Source Pollution of Typical Land Use in A Micro-Watershed in Hilly Red Soil Region

科学识别不同土地利用方式下的径流污染输出特征是治理流域面源污染的前提.以南方红壤丘陵地区小流域为例,野外实地观测对比了不同降雨特征下林地、种植用地和建设用地的水文过程和面源污染物输出过程.结果表明,土地利用方式影响着地表径流的水文水质过程,典型降雨下3类用地类型产流时间及产流累积雨量的特征为:建设用地(9 min,2.0 mm)、种植用地(35 min,11.4 mm)和林地(108 min,24.0 mm);而3种用地类型的总悬浮物(TSS)、总氮(TN)和总磷(TP)的污染物浓度、形态、氮磷比变化及输出强度等污染输出过程特征也呈现明显差异.典型降雨下不同用地类型具有相似的污染输出阶段,径流初期的TSS、TN和TP质量浓度均偏高,之后逐步趋于稳定;产流过程的前30 min贡献TSS、TN及TP负荷的范围均在23%~43%之间.年尺度下,各用地类型对TN和TP负荷的贡献率及单位面积负荷比存在明显差异,表现为种植用地污染负荷贡献最高(57%和45%),而建设用地单位面积负荷比最高(9.50~12.50).结果亦表明小流域面源污染关键源区的分布具有时空动态变化特征,由汇水单元内的用地类型组成和年降雨特征等综合决定;随着次降雨量的增加,主要贡献源由建设用地向种植用地动态转变,治理时需要根据关键源区的分布特征及下垫面产流过程规律进行针对性生态拦截.

Scientific identification of runoff output characteristics of different land use patterns is the premise of controlling non-point source pollution in watersheds.The hydrology and output process of non-point source pollutants of forest,planting,and construction land with different rainfall characteristics were observed using a microwatershed in a low mountain and hilly region of Southern China.The results showed that land use affected the hydrological characteristics and water quality processes of runoff.The characteristics of runoff generation time and cumulative rainfall under typical rainfall conditions were as follows:construction land(9 min,2.0 mm),planting land(35 min,11.4 mm),and forest land(108 min,24 mm).There were significant differences in the three land use types in the pollution output process characteristics,such as pollutant concentration of total suspended matter(TSS),total nitrogen(TN)and phosphorus(TP),their components,N/P ratio change,and output intensity.Under typical rainfall,different land use types had similar pollution output stages,the mass concentrations of TSS,TN,and TP in the initial runoff were high,and then gradually stabilized.In addition,the first 30 min of the flow generation process contributed to the TSS,TN,and TP loads within the 23%-43%range.At the annual scale,there were significant differences between the contribution rate of each land use type to TN and TP load and ratio per unit area;the highest contribution to total pollution load was planting land(57%and 45%),while the highest in pollution load per unit area was construction land(9.50-12.50).The results also showed that the distribution of key non-point source areas had different spatial and temporal dynamics,which was comprehensively determined by the land use types in catchment units,the characteristics of annual rainfall,among other factors.With the increase in rainfall,the main contribution non-point source pollution in the micro-watershed changed from construction land to planting land.Targeted ecological interception strategies should be implemented based on the distribution characteristics of key source areas and characteristics of underlying surface runoff production process.