石漠化区薄土层坡地雨水转化及土壤侵蚀影响因素分析

Influencing factors of rainwater transformation and soil erosion in thin soil hillslope of rock desertification regions

为了探究影响喀斯特坡地雨水转化及土壤侵蚀的影响因素,该研究采用人工模拟降雨方法,降雨强度选取50、75和100 mm/h,降雨次数为相同降雨强度下的连续3次降雨,坡度为5°、15°和25°,坡地包括地下基岩具有裂隙的地下裂隙坡地和地下基岩无裂隙的无地下裂隙坡地,研究了不同降雨强度、降雨次数和坡度下喀斯特坡地地表-地下的径流和土壤侵蚀变化。结果表明:1)两种坡地的地表径流率随降雨强度、降雨次数和坡度的增加而增加;壤中流率随降雨强度和坡度的变化也呈相同的趋势,但随降雨次数增加,两种坡地的壤中流率减少;岩土界面流率和地下裂隙流率随坡度和降雨次数增加而减少,随降雨强度增加先增大后减小。2)在降雨强度(50和75mm/h)、降雨次数(第1场)和坡度(5°和15°)较小时,坡地径流以岩土界面流和地下裂隙流为主,分别占总雨水的24%~39%和28%~51%;随着影响因素增强,两坡地径流转变为以地表径流为主,分别占总雨水的30%~50%和25%~43%。3)降雨强度和坡度是驱动两个坡地地表土壤侵蚀的主要驱动力(P<0.01),但降雨强度、降雨次数和坡度对两坡地地下土壤侵蚀的影响较小(R^(2)<0.3,P>0.05);总体上,无地下裂隙坡地和地下裂隙坡地土壤侵蚀以地表土壤侵蚀为主,分别占总侵蚀量的54%~97%和39%~96%;以岩土界面侵蚀或地下裂隙侵蚀为辅,分别占总侵蚀量的1%~45%和2%~60%。研究结果可为理解识别喀斯特坡地雨水转化和土壤侵蚀驱动因素以及喀斯特石漠化防治提供参考。

Karst landforms are characterized by surface-underground double hydrological structure, due to strong karstification.There are very complex rainwater transformations and soil erosion under the double hydrological structure. It is a high demand to clarify the influencing factors of rainwater transformation and soil erosion on karst hillslopes. In this study, a rainfall simulation was performed on karst hillslope to explore the runoff and soil erosion at the surface and below ground under different rainfall intensities, slope gradients, and rainfall times. Among them, the rainfall intensities were 50, 75, and 100 mm/h;while the rainfall time was successive three ones at 24 h interval under similar rainfall intensity(1st, 2nd, and 3rd);the slope gradient were 5°, 15°, and 25°;two types of hillslope were with/without the fissure on underground bedrock(No Underground Fissure Flow(NUF) and Underground Fissure Flow(UFF)). Two hydrological situations were selected, including two soil boxes with/without fissures at the bottom. The length, width, and height of the two soil boxes were 1, 0.5, and 0.15 m,respectively. The Surface Runoff(SR) and Subsurface Runoff(SBR) of two hillslopes treatment were collected through the experimental soil boxes, together with the Soil Rock Interface Flow(SRIF) of NUF and UFF. The results showed that 1) the SR rate increased with the increase of rainfall intensity, slope gradient, and rainfall time;a similar trend was also found in the SR rate under different rainfall intensity and slope gradient. But the SBR rate of the two hillslopes decreased with the increase in rainfall time. The NUF and UFF rate of soil rock interface increased firstly, and then decreased, with the increase of rainfall intensity, whereas, decreased with the increase of slope gradient and rainfall time. 2) The soil-rock interface flow(24%-39% of the total rainwater) of NUF and UFF(28%-51% of the total rainwater) dominated the runoff process of karst hillslopes, where there were small rainfall intensity(50 and 75 mm/h), slope gradient(5°and 15°) and rainfall time(First rainfall). However, the SR(30%-50% of total rainwater and 25%-43% of total rainwater) dominated the runoff processes of two treatment hillslopes with the increase of factors. 3) There was also an important role of drive factor in the rainfall intensity(The NUF and UFF regression coefficient: 0.61 and 0.63,(P<0.01), the same as the slope gradient(The NUF and UFF regression coefficient:0.38 and 0.38) during surface soil erosion process of two hillslopes treatment(P<0.01). There was a very slight effect of rainfall intensity, slope gradient, and rainfall time on the soil erosion below the ground of the two hillslopes treatment. The R^(2) of the regression equation was also less than 0.3, indicating no significant(P>0.05) effect of rainfall intensity, slope gradient,and rainfall time on soil erosion below ground. Overall, the surface soil erosion dominated the soil erosion process of NUF and UFF, where the ratio of surface soil erosion to total soil erosion were 54%-97% and 39%-96%, respectively. The soil-rock interface erosion or underground fissure erosion was the secondary erosion process(1%-45% or 2%-60%). These findings can provide the basic information for a better understanding of the dive factors of rainwater transformation and soil erosion on karst hillslopes.