三峡库区石盘丘小流域氮磷输出形态及流失通量

小流域作为三峡库区非点源污染源头,是缓解水体水质恶化的重点防控对象.在三峡库区选取具有多种土地利用类型的石盘丘小流域为研究对象,对流域出水口断面水量水质进行连续监测,分析了小流域氮、磷污染物随降雨径流流失的浓度及形态变化特征,并计算小流域的污染物流失通量,分析影响氮、磷养分流失的主要人为和自然因素,对农业非点源污染特别是三峡库区的农业非点源污染研究具有相当重要的现实意义.结果表明,流域降雨量随季节变化明显,降雨多分布在4～6月,为小流域氮、磷流失的主要输出时期,占全年总氮、总磷负荷的58.94%和67.60%.石盘丘小流域年径流总量为8.02×10~4 m~3,总氮年流失通量为5.04 kg·hm~(-2),其中以硝态氮(2.54 kg·hm~(-2))为流失主体;输出总磷为0.534 kg·hm~(-2),可溶性总磷(0.422kg·hm~(-2))占总磷流失通量的79.00%.因此,对于石盘丘小流域来说,需要注意防范施肥和降雨期重合时水田氮磷流失.

Characteristics of Nitrogen and Phosphorus Output and Loss Flux in the Shipanqiu Watershed, Three Gorges Reservoir Area

As the source of non-point pollution in the Three Gorges Reservoir Area, small watershed is a key control object in alleviating deterioration of water quality. In the Three Gorges Reservoir Area, the Shipanqiu small watershed with various land-use types was selected as the research object, and the water quantity and quality of the outlet section of the watershed were continuously monitored. We carried out analysis of the small watershed runoff loss and nitrogen and phosphorus pollutants with concentration, analyzed the morphology change characteristics of runoff erosion, calculated the small watershed of pollutant emission flux, and analyzed the nitrogen and phosphorus nutrient loss and main human and natural factors, especially in the Three Gorges Reservoir Area of agriculture where nonpoint source pollution research has important practical significance. The results showed that the rainfall in the watershed varied significantly with the seasons, and the rainfall was mainly distributed from April to June, which was the main output period of nitrogen and phosphorus loss in the small watershed, accounting for 58.94% and 67.60% of the total nitrogen and phosphorus load, respectively, in the whole year. The total annual runoff in the Shipanqiu small watershed was 8.02×10⁴ m³, and the annual total nitrogen loss flux was 5.04 kg·hm^-2, of which nitrate nitrogen (2.54 kg·hm^-2) was the main part. The total phosphorus output was 0.534 kg·hm^-2, and the soluble total phosphorus (0.422kg·hm^-2) accounted for 79.00% of the total phosphorus flux. The loss flux of total nitrogen was 9.51 times that of total phosphorus, and the non-point source pollution risk of nitrogen was much greater than that of phosphorus. Therefore, for the Shipanqiu small watershed, it is especially important to prevent nitrogen loss in paddy fields when fertilization and rainfall coincide.