黄土高原典型切沟土壤水分时空分布特征及其影响因素

研究切沟土壤水分及干层时空分布特征,有利于提高地区水资源利用效率及植被恢复效益。以神木市六道沟小流域典型切沟为研究对象,对土壤水分状况进行定位监测,分析沟底、沟缘和沟岸土壤水分时空分布、干层分布特征及其影响因素。结果表明:沟底土壤含水率由沟头至沟口呈明显增加趋势。沟底、沟缘和沟岸0~480 cm剖面土层平均含水率分别为17.1%、13.5%和14.4%。沟底0~480 cm剖面土层平均储水量为80.54 cm,沟缘及沟岸分别为67.49 cm和71.05 cm。地形和土壤质地是影响土壤储水量的主要因素;土壤储水量与距沟头距离、土壤黏粒、粉粒含量呈极显著正相关。沟底、沟缘和沟岸均有干层出现,且主要集中在靠近沟头位置,平均厚度和起始深度分别为243 cm和257 cm,平均含水率为9.5%。沟底、沟缘和沟岸干层平均厚度分别为100 cm、286 cm和331 cm。研究结果可为该区域土壤水资源管理和土壤水库评价提供理论依据。

Characteristics and Influencing Factors of Spatiotemporal Distribution of Soil Moisture in Typical Gully of the Loess Plateau

Objective] Although large-scale afforestation improves vegetation coverage of the Loess Plateau, it also leads to soil moisture deficit in this region. The emergence of dry soil layers slows down or cuts off the exchange of soil moisture between the upper and lower layers, thus causing deterioration of the soil environment and degradation of the vegetation. As an important part of the slope-gully system on the Loess Plateau, the development and evolution of gullies change the soil moisture on the slope, and the distribution and utilization efficiency of water resources in the catchments. However, so far little has been done on temporal and spatial distribution of soil moisture in gully and its surrounding areas.Method] In this study, a typical gully in Liudaogou Watershed of Shenmu County was selected as the research object for monitoring soil moisture. In the gully three sample strips were laid out at the bottom (along the centerline), the edge (1 m wide) and the gully bank (20 m wide). Following the direction of the gully, 12 observation points were arranged at the gully bottom from the head to the outlet of the gully, and 7 observation points were set up along the gully edge and bank, separately. At each point, a hole was prepared with an auger to the depth of about 480 cm at the bottom section, and approximately 980 cm at the edge and bank sections for insertion of a neutron tube (CNC503DR) for in-situ observation of soil moisture. Measurement was made at 10 cm intervals along the 0-100 cm soil profile, and at 20 cm intervals when it got below 100 cm. Then soil moisture distribution was characterized and dried soil layers were analyzed and compared, as well as its influencing factors. Soil samples were collected while holes were prepared.Result] (1) Soil moisture conditions were better at the bottom than at the edge and the bank, and water deficit was the most obvious at the edge. At the bottom section, soil moisture content increased obviously along the gully from the head to the outlet, and higher in the deep layers than in the surface soil layer, of which the 0-10 cm soil layer was the lowest in moisture content. The mean soil moisture content of the 0-480 cm soil profiles was 17.1% at the bottom, 13.5% at the edge and 14.4% at the bank; (2) In the soil layer above 480 cm, the mean soil water storage capacity was 80.54 cm at the bottom, 67.49 cm at the edge and 71.05 cm at the bank; (3) Topography and soil texture were the main factors affecting soil water storage capacity, and soil water storage was positively related to distance from the gully head, soil clay and silt content; (4) Dry soil layers in the gully area mainly appeared at the gully head, with an average thickness of 243 cm, an average initiation depth of 257 cm, and an average water content of 9.5%. The average thickness of the dry soil layers at the bottom, edge and bank was 100 cm, 286 cm and 331 cm, respectively.Conclusion] The existence of gullies affects distribution of the soil moisture in this area and enhances its variability. Dry soil layers in this region exist stably for long and in case of severe droughts, they are likely to keep on growing. All the findings may serve as a theoretical basis for management of soil moisture resources and evaluation of soil reservoir in this area.