| Hulun Lake is the fifth largest freshwater lake in China, and also the one with the most widespread basin area in Inner Mongolia. The lake, together with the Great Khingan, has built up an ecological barrier for the north China in prevention of its ecological security. The ecological vegetation change of grassland does affect the ecological and hydrological processes of the whole basin. So, we need to find out the reason why certain indexes have changed and the differences in hydrologic process caused by the changes in vegetation in order to make clear about the influence vegetation has on the hydrologic process.In this paper, the Hulun Lake basin is taken as the study area. First,The scope of the pasture was determined by different grazing systems. Then, the field observation experiments were carried out under various grazing systems. Hereafter, I began to monitor the condition of vegetation growth and the process of rainfall interception within the trial districts. In the end, data from both outside observations and indoor tests are used to analyze the vegetation intercept, rainfall and soil hydrological characteristics of the area. The outcome shows as below.I. There are significant differences in physical properties and chemical properties of the three grazing kinds of pasture soil in depth of0-80cm (P<0.05). However, the differences are less significant in the same pasture soil of different depth. Porosity and moisture content generally go down along with the increase of the soil depth.Vertical distribution of the chemical indicators is apparent that they basically decreases with the growing depth, except the versa PH.II. Rainfall simulation experiments on the three grazing pastures indict the comparative results of rainfall runoff and sediment concentration should be:rest grazing> rotation grazing> free grazing(constant rainfall intensity and slope). While, the addition of soil moisture after the rainfall is that:rest grazing> free grazing>rotation grazing.The main erosion soil for the three pastures are:sandy loam soil for the rest grazing one; half silty loam along with half sandy loam soil for the rotation grazing one; silty loam soil for the free grazing one.Ⅲ. Under the rest grazing, rotational grazing and grazing systems, the intercept out of water immersion method is respectively:0.468mm;0.320mm;0.271mm. Meanwhile, the results out of rainfall simulation method are respectively:0.957mm;0.613mm;0.431mm. Still, Leaf area index, coverage, density, biomass and other indicators among the three kinds of grazing pastures have significant differences(P<0.05). What’s more, the height and fresh weight of single vegetation have a significantly linear and positive correlation related to intercept quantity.IV. The areas of the three grazing grassland were determined by the NDVI indexes extracted from Landsat5TM images. Ignoring the rainfall inhomogeneity, I make an estimation on the total rainfall intercept of the whole basin in combination of the relationship between vegetation coverage and intercept quantity. If the rainfall to the whole basin is greater than or equal to30mm, the interception quantity of rest grazing, rotational grazing and free grazing pastures are respectively about4.995×105m3;3,283×106m3;2.679×106m3. The total intercept quantity is about6.462×106m3. |
