紫色土小流域土壤及氮磷流失特征研究

Nitrogen,phosphorous and soil losses by runoff in a farmland-dominated watershed in purple soil region

紫色土区土壤及其养分流失对长江水环境产生严重威胁。然而,有关该地区自然降雨侵蚀下土壤及氮磷流失规律的研究却较为少见。以紫色土农田利用为主小流域为研究对象,监测自然降雨侵蚀下土壤及其氮磷的流失过程,以期服务于流域尺度土壤及养分流失的模拟与控制。结果表明,次降雨径流含沙量与流量的变化基本同步,峰值含沙量往往出现在峰值流量处或略有提前,此后,含沙量迅速降低。硝态氮流失浓度与流量的变化成反比,峰值流量处流失浓度一般达到最低,此后,随着流量的降低,其流失浓度存在较为明显的升高过程。铵态氮与水溶性磷的流失表现为剧烈波动的变化特征。氮素流失的主要形态是硝态氮,其占到次降雨无机氮流失总量的88%～97%。

Soil and nutrient losses from purple soils have been reported to increase pollution of the Yangtze River.However,few studies addressed their concentration variations in runoff under natural rainstorms.Soil,nitrogen and phosphorous losses by runoff were investigated in a farmland-dominated watershed in the purple soil regions for the purpose of erosion control and simulation.The peak sediment concentrations generally preceded or occurred simultaneously with their peak runoff rates for most of runoff events.Sediment concentration variations usually followed a similar degression trend during the period of decreasing runoff rate.In contrast,nitrate concentration in runoff was inversely proportional to runoff rate,which arrived to the lowest at peak runoff rate.A notable increasing variation of nitrate concentration after peak runoff rate was observed for most of runoff events.The concentrations of ammonium and dissolved reactive phosphorus substantially fluctuated during a runoff event.Nitrate was the main form of inorganic nitrogen loss,which account for 88%～97% depending on various rains.