高寒草地植被覆盖变化对土壤水分循环影响研究

Study on the Influence of Vegetation Changeon Soil Moisture Cycle in Alpine Meadow

土地覆盖变化对流域水平衡的影响是流域水文学和生态水文学研究的关键问题之一.以黄河源区两个典型小流域为研究对象,通过对流域不同植被类型与植被覆盖土壤的水分含量、入渗过程、蒸散发特征的测定,研究了高寒草地植被覆盖变化对土壤水分循环的影响.结果表明:广泛分布于青藏高原河源区的高寒草甸草地,植被覆盖度与土壤水分之间具有显著的相关关系,尤其是20cm深度范围内土壤水分随植被盖度呈二次抛物线性趋势增加;在保持其原有的植物建群和较高覆盖度时,土壤上层具有较高持水能力,降水通过表层向深层土壤的渗透速度缓慢,且具有较均匀的土壤水分空间分布,水源涵养功能明显;高寒草甸草地退化后的高山草甸土壤趋于干燥,持水能力减弱,即使进行人工改良以后,土壤水分含量与持水能力也不会有明显改善.保护河源区原有高寒草甸草地对于河源区水文过程意义重大.

The influence of vegetation change on the water balance in a drainage area is one of the pivotal problems in the study of hydrology and eco-hydrology. In this paper, two typical small drainage areas in the source regions of the Yellow River were taken as examples. For the alpine meadow widely distributed in the river source regions in the Tibetan Plateau, measuring the soil moisture content, infiltration process and evapotranspiration characteristics under different vegetation types and coverage conditions in the drainage areas shows that there was a significant correlation between the vegetation coverage and the soil moisture. Especially, the increasing of soil moisture with vegetation coverage could be described as a quadratic parabolic equation within the depth of 20 cm. When the original plant community is kept and coverage is higher, the water retention ability would be higher in the upper layers of soil. Meanwhile, the rate of water infiltrating from the surface to deeper and surface evapotranspiration would be lower, so the function of water conservation would be obvious. After the alpine meadow degrading, the meadow is getting dry, water retention ability reduces and surface evaporation becomes higher. Even if the meadow is amended artificially, soil moisture content and water retention ability cannot be improved obviously, and surface evapotranspiration would increase. It is very important to protect the original alpine meadow for the hydrological process in the river source regions.