| The Loess Plateau of China is located at a transitional area where the semi-humid climate is changing into the semi-arid and arid climate. This makes the eco-environment of the plateau very fragile. Because of both natural and man-induced causes, up to now, the Loess Plateau of China is being a colossal degraded eco-system. In such an area, water is the controlling factor which refrains the growth of vegetation and crop production. So, the study on the water eco-environment of the plateau is significant to vegetation recovery and eco-reconstruction.Based on the achievements of related previous studies on this issue and the unsolved problems, here, four aspects are concentrated in this dissertation for the issue. They are: (1) Background of the soil water environment of the plateau; (2) Reality of the soil water environment of the plateau; (3) Vegetation capacity of the soil water of the Plateau; and (4) Spatial differences study for the soil water eco-environment of the plateau using GIS.The objectives are approached both by field survey and lab analysis. The following results are obtained based on the field data and analyses:1. The spatial heterogeneity of climate and precipitation and the water resources in the Loess Plateau area are analyzed and discussed.The water eco-conditions are derived from the regional precipitation and the water resources of the plateau area. Results show that: (1) The precipitation of the Loess Plateau appears to descend spatially from east to west and from south to north. At the southeast, the maximum average annual precipitation can reach 950mm, and the minimum at the northwest is just 150mm. These reflect an obvious continental climate characteristic. (2) Parts of the area show apparent local climatic properties because of the influence of topography, landcover, and so on. Precipitation in mountainous and forest area is usually more affluent than in vicinity, this creates a typical mosaic structure of precipitation distribution like the islands. (3) Soil water is the most significant form of water resources, which is the only water for vegetation uptake. The utilization of surface water resources in areas of the Loess Plateau is in full extent, so the balance between supply and demand is a serious problem. However theuse of groundwater has rooms to be extended and the water-using efficiency is relatively low.2. The concept of soil water background is developed in this dissertation. Meanwhile, most aspects about this perspective are concerned, which include quantification of the soil water background of the plateau area, the regional spatial variation of soil water background and variation along the slope, mosaic structure and seasonal changes etc. The results show that: (1) For the fundamental circumstance for vegetation development is the original debilitated slope, so the perspective of soil water background specially for the Loess Plateau refers to the soil water conditions on the original slope. (2) The value of soil water background appears to be a descending trend from south to north based on the difference of vegetation zones. In the forest zone, soil moisture contents beneath 3m depth from the soil surface are more than 12% usually; in the forest-pasture zone, the values of soil moisture content beneath 4m depth underground are more than 6% and stable, and tend to be ascending while the depth increases; but the values in the dry pasture zone is lingering between 4% to 6% from the surface layer to sub-layers. Vertically, the values of the upper 3m soil layer in the forest zone and upper 4m soil layer in the forest-pasture zone increase dramatically with depth, and the soil moisture contents beneath the depths seem to be stable, but they vary a little bit along the profile in the pasture zone. (3) The distributions of both regional soil moisture and available soil water are similar, high in the south and low in the north, and have a mosaic structure similar to the regional precipitation distribution. (4) The soil moisture of the original slope is inf...
|
PDF Full Text Request