三峡山地不同类型植被和坡位对土壤水文功能的影响

土壤层下渗和贮蓄水分的水文功能是森林保持水土、涵养水源的基础。以三峡山地大老岭林区为研究区,采集常绿林、落叶林和草地覆盖下不同坡位的原状土样,测定其饱和导水率和水分特征曲线,分析植被类型和坡位对土壤水分参数和库容的影响。结果表明:常绿林地的入渗性能最好,饱和导水率为7.80—322.81 cm/d,大于落叶林地(0.33—137.03 cm/d)和草地(0.84—115.80 cm/d);坡位间差异表现为上坡高于下坡。不同样地的饱和含水量差异较小,但毛管持水量和田间持水量差异明显,草地最大,为20.77%—50.39%;不同坡位比较表现为下坡高于上坡。不同样地土壤水库容量差异较大,由田间持水量得到的库容量占总库容量的百分比以草地最大(63.25%),其次是落叶林地,常绿林地最小;坡位上表现为下坡的田间持水库容大于上坡。饱和导水率与土壤总孔隙度、有机质含量呈显著正相关,与容重呈显著负相关;饱和含水量、毛管持水量、田间持水量均与土壤总孔隙度、有机质含量和粉粒含量呈显著正相关,与容重、砂粒含量呈显著负相关。综合以上,草地持水性能最强,利于保蓄水分,常绿林地最弱,更利于水分入渗,补给地下水,下坡位的持水性能强于上坡位。

Influence of vegetation coverage and topographic position on soil hydrological function in the hillslope of the three gorges area

Rainfall infiltration through soil profile forms a key process of water cycle in the critical zone of terrestrial ecosystem. The hydrological function of soil pedons on transporting and accumulating rainwater constructs the foundation of forestland on soil and water conservation in mountainous area. To study impacts of vegetation cover and topographic position on soil hydrologic features of mountain area, three separated hillslopes covered with different vegetation in a typical catchment of the Dalaoling Forest Region were selected as the study area, where just located at 40km upstream of the Three Gorges Dam. Undisturbed soil cores were sampled with cutting rings from upslope and downslope positions. Saturated hydraulic conductivity and soil water characteristic curves of these soil cores were measured indoors, using constant water head method and centrifugal method, to analyze the influence of vegetation cover and topographic position on soil hydrological parameters and water storage. The results indicated that soil infiltration ability of evergreen forest land was the largest, and its soil saturated hydraulic conductivity was 7.8-322.81 cm/d, which was relative greater than that of deciduous forest soil (0.33-137.03 cm/d) and grassland soil (0.84-115.80 cm/d). Variation between different topographic positions revealed that the saturated hydraulic conductivity of upslope sites greater than that of downslope sites. Compared with the less difference between soil saturated water content, capillary moisture capacity and field capacity of six experimental sites varied significantly, and the two capacity parameters of grassland soil (20.77%-50.39%) were greater than that of forestland soil. Soil capillary moisture capacity, field capacity and wilting water content of upslope sites were less than those of downslope sites according to the comparison between the sites under the same vegetation coverage. Soil storage capacity varied apparently among six sites. The percentage of reservoir capacity obtained from field capacity accounting for total soil water storage capacity was largest in grassland sites, at 63.25%, while that of evergreen forestland sites was the least with only 55%. Comparison among topographic positions indicated the result of downslope sites was larger than that of upslope sites. Correlation analysis between soil water characteristic parameters and soil properties showed saturated hydraulic conductivity had significant positive relation with soil total porosity and organic matter content, and significant negative relation with soil bulk density. Soil saturated water content, capillary moisture content and field water capacity were significantly positively correlated with soil total porosity, organic matter content and silt particle content, and negatively correlated with soil bulk density and sand particle content. In conclusion, the soil water holding capacity of grassland was the largest among all observed sites, which was conducive to accumulate soil water, while evergreen forestland had the largest water infiltration rate which was prone to recharge underground water. For different topographic positions, downslope sites had larger soil water storage than upslope sites.