水蚀过程中土壤重金属元素的迁移特征

Migration Characteristics of Heavy Metals in Soil During Water Loss Process

[目的]探索水蚀过程坡耕地表层土壤重金属元素迁移特征,为中国喀斯特水土侵蚀地区的土壤质量保护和防控重金属元素迁移扩散研究提供指导。[方法]用人工模拟降雨试验,研究不同雨强(50,70,90,120 mm/h),不同坡度(10°,15°,20°和25°)下坡耕地表层土壤重金属元素(Cu, Ni, Cd和Cr)随径流及侵蚀过程中的迁移特征。[结果](1)产流产沙量随降雨强度、坡度的增加而增加并逐渐趋于稳定,不同降雨强度和坡度下产沙量临界坡度为20°。(2)表层土壤重金属在侵蚀过程中主要以颗粒态形式存在,且迁移量与降雨强度成正比。在雨强120 mm/h和坡度20°下,颗粒态重金属最先达到流失量峰值;溶解态重金属随降雨强度呈波动变化,除溶解态Ni在50 mm/h下达到最大变化范围0.004 4 mg/L,Cu, Cd和Cr均在70 mm/h达到流失最大变化范围,其中Cr变化范围最大(为0.009 8 mg/L)。溶解态重金属流失量随坡度变化无明显规律。(3)颗粒态重金属流失量与产沙量拟合结果显示Cr(R^(2)=0.99)的拟合度好,因此产沙量可以较好地预测颗粒态Cr的流失量。[结论] 20°是产沙量的临界坡度,重金属迁移主要以颗粒态形式迁移且产沙量与重金属元素(Cu, Ni, Cd和Cr)拟合效果好,说明重金属元素(Cu, Ni, Cd和Cr)与产沙量之间存在较强的相关性。

[Objective]The migration characteristics of heavy metals in the surface soil of sloping farmland during water erosion process were analyzed in order to provide guidance for soil quality protection and for defense strategies against heavy metal migration and diffusion in karst soil erosion areas in China.[Methods]A simulated rain experiment was used to study loss characteristics of heavy metals(Cu,Ni,Cd,and Cr)from runoff and erosion in farmland under different slope conditions(10°,15°,20°,and 25°)and rainfall intensities(50,70,90,and 120 mm/h).[Results]①Initial runoff and sediment yield increased with increasing of rainfall intensity and slope,then tended to gradually become stable.The critical slope for sediment yield was 20°under different rainfall intensities and slopes;②Heavy metals mainly existed in granular form in the erosion process of topsoil,and migration amount was proportional to rainfall intensity.Heavy metal loss in granular form first reached a peak value under a rainfall intensity of 120 mm/h and a slope of 20°.Dissolved heavy metals varied with rainfall intensity,except for dissolved Ni that reached a maximum variation range of 0.0044 mg/L at 50 mm/h.Cu,Cd,and Cr all reached a maximum variation range of loss at 70 mm/h,and the maximum variation range of Cr was 0.0098 mg/L.The loss of dissolved heavy metals had no obvious relationship with slope change.③The heavy metal particle loss was related to sediment yield,and the high coefficient of determination for Cr(R^(2)=0.99)indicated that sediment yield could well predict Cr particle loss.[Conclusion]20°is the critical slope for sediment yield,and that migration of heavy metals is mainly in granular form.The fitting effect between sediment yield and heavy metal elements(Cu,Ni,CD,and Cr)is good,indicating that there is a strong correlation between heavy metal elements(Cu,Ni,CD,and Cr)and sediment yield.