喀斯特地区坡面不同土地利用方式水土流失及磷素输出对次降雨特征的响应

Response of soil erosion and phosphorus losses to individual rainfall under different land uses at Karst slopes

为探究喀斯特地区坡面不同土地利用方式下水土流失及磷素输出对次降雨特征的响应,对喀斯特地区不同土地利用方式(水保林、耕地、自然草地、裸地、经果林)坡面场次降雨的水土流失和磷素输出进行了分析。结果表明:5种土地利用方式的径流系数由大到小整体表现为裸地>自然草地>耕地>水保林>经果林,而单位面积产沙量、单位面积磷流失量整体表现为耕地>裸地>经果林>水保林>自然草地。其中耕地和裸地在大雨量、高强度降雨事件的影响下径流系数、单位面积产沙量、单位面积磷流失量急剧增大。雨强是影响水土流失、磷素输出的重要因素,可以很好地拟合水土流失量。径流中磷素输出以颗粒态磷(PP)为主,占总磷(TP)的比例介于75.47%~97.91%之间。降雨引起的耕地径流[0.73 mg·L-1<ρ(TP)<2.49 mg·L-1]、裸地径流[0.10 mg·L-1<ρ(TP)<0.50 mg·L-1]和经果林径流[0.13 mg·L-1<ρ(TP)<0.46 mg·L-1]磷输出对受纳水体磷的含量有增加的风险,而自然草地径流[0.03 mg·L-1<ρ(TP)<0.09mg·L-1]影响较小。坡面水土流失和磷素输出与降雨过程、土地利用方式关系密切,可以通过优化土地利用结构、减少人为扰动有效防治水土流失,减轻流域面源污染。

In order to understand the response of soil erosion and phosphorus losses to individual rainfall under different land uses at Karst slopes, water and sediment samples were collected from different Karst slopes. These samples comprised conservation forest, farmland, natural meadow, bare land, and economic fruit forest land uses. The results indicated that the descending order of runoff coefficients for the five land-use types were as follows：bare land 〉natural meadow 〉farmland 〉conservation forest 〉economic fruit forest. The sediment yield and phosphorus losses per unit area were（ in descending order） as follows：farmland〉bare land〉economic fruit forest〉conservation forest〉natural meadow. Under large rainfall and high-intensity rainfall conditions, runoff coefficients, sediment yield per unit area, and phosphorus losses per unit area of farmland and bare land increased sharply. Rain intensity was a significant factor that affected soil erosion and phosphorus losses, which fitted well with the amount of soil erosion. Particulate phosphorus （PP） was the main loss of total phosphorus （TP）, ranging from 75.47% to 97.91%. Farmland runoff[0.73 mg·L^-1 〈p （TP）〈2.49 mg·L^-1], bare land runoff[0.10mg·L^-1〈p（TP）〈0.50 mg·L^-1] and economic fruit forest runoff[0.13 mg·L^-1〈p （TP）〈0.46 mg·L^-1] could lead to phosphorus loadings increasing in receiving waters, while that of natural meadow runoff[0,03 mg·L^-1〈p（TP）〈0.09 mg·L^-1] had minor impacts on pollutant loadings in receiving waters. Soil erosion and phosphorus losses correlated strongly with precipitation processes and land uses, suggesting that land-use structure optimization and human disturbance reduction could be an effective method to mitigate soil erosion and non-point source pollution.