The Research Of Hydrological Processes Of Micro-region In Minqin Oasis-desert Transitional Zone

Widespread micro-region(Nitraria tangutorum sand inter-dune,clay sand barrier + Haloxylon ammodendron forest,Clay plains) in Minqin oasis-desert transitional zone was selected as research object, through access to rainfall data, field survey, soil sampling, artificial rain, natural precipitation and follow-up observations of soil moisture, soil microprocess research and infiltration water Spatial Dynamic Change, The results showed that:(1)The precipitation in the study area is small and the annual difference between a normal distribution, mainly concentrated in the July to September, the average of monthly rainfall for many years ranged from larged and the differences in the distribution of seasonal rainfall. Rainfall occurred at night, if not considered changes in the month, the precipitation between day and night have a significant correlation and was proportional. Compared to heavy rain on the order of their frequency and magnitude of rainfall over large differences in precipitation frequency decreases with rainfall series.(2)The features of Micro-runoff: The distance of water collection is short, The area of water collection is small, The volume of water collection is low; The features of runoff process: Storage- infiltration and overland flow stage.The topsoil clay and powder content in accumulated area of fixed Nitraria tangutorum sand inter-dune lowland is lower than the runoff generation area, while the fine sand content in deep layer of runoff generation area is greater than the accumulated area; soil in two areas of clay flat land mainly consists of coarse and fine sand, and clay particles are better in runoff generation area than in accumulated area. Soil in the clay sand barrier + Haloxylon ammodendron forest is mainly coarse sand and the structure is single.(3)The rainfall intensity-runoff curves was in liner trend in runoff area of microregion with Clay sand barrier + Haloxylon ammodendron forest and Nitraria tangutorum sand inter-dune.(4)After the 27.4 mm rainfall,The soil moisture infiltration in core area, transition area and margin area of clay sand barrier + Haloxylon ammodendron forest at 0~14h fast; 14~86h decreased; 86 h after infiltration rarely. Nitraria tangutorum sand inter-dune microregion 0~14h rapid infiltration(transition area > margin area > core area), but the result is far less than clay sand barrier + Haloxylon ammodendron forest in the three areas; 14~74 h, infiltration rate slows; 74~254 h, three districts are still continuing infiltration; to 254 h its results depth less than the three areas of clay sand barrier + Haloxylon ammodendron forest.(5)After precipitation in different regions of the two types of micro-region 20 cm surface sampling, analysis studied: The soil moisture evaporation loss is small within 0~8 h in clay sand barrier + Haloxylon ammodendron forest(core zone> transition area > margin area); 8~86h larger loss; 86~254h, three areas of the layer of soil moisture decreased, but the rate slowed. Nitraria tangutorum sand inter-dune 0~14 h loss rate(core area> Margin area> transition area) more slowly; 14~74h the losses results similar process with clay sand barrier + Haloxylon ammodendron forest micro-region 8~86 h, the loss significant of soil moisture(core area> margin area> transition area); 74~254h the soil moisture loss still continue, but the rate slowed, the soil water content: core area> margin area> transition area.(6)Different types of micro-regions(clay sand barrier + Haloxylon ammodendron forest, Nitraria tangutorum sand inter-dune) rainfall gradient micro-lysimeter day water loss in the process of substantially similar. Two micro-regions Third District evaporation process has similarities loss amount: margin area > transition area > core area.The evaporation throughout each day of two types micro-regions: 15 mm precipitation corresponds to evaporation> 10 mm precipitation evaporation corresponds> 5 mm precipitation corresponds to evaporation.(7) The early of 27.4 mm rainfall,three areas for two types of micro-regions on the 0~140 cm soil moisture in the vertical profile was high on low gradient distribution. The maximum infiltration depth of clay sand barrier + Haloxylon ammodendron forest microregion: the core area of 80 cm, and the edge of the transition zone of 60 cm; among Nitraria tangutorum sand inter-dune: the core area of 40 cm, the transition and margin area of 60 cm. clay sand barrier + Haloxylon ammodendron forest micro-region, Soil moisture dynamics at three levels: low level, are about 20 cm; second active layer, the core area of 20~80 cm, the transition and margin area 20~60 cm; stabilizing layer, the core area of 80~140 cm, transition and fringe 60~140 cm. Nitraria tangutorum sand inter-dune microregion: low level, the core area of 0~15 cm, the transition and margin area of 0~20 cm; water active layer, the core area of 15~30 cm, the transition zone 20~40 cm, marginal zone of 20~60 cm; soil moisture stable layer: the core area of 30~140 cm, the transition 40~140 cm and fringe 60~140 cm.(8) The building group vegetations for Nitraria tangutorum sand inter-dune and clay sand barrier + Haloxylon ammodendron forest micro-region are gradual degradating, and then shallow-rooted shrubs(Limoniumau-reum and Reaumuria songarica) and herbaceous vegetation(Eragrostis pilosa, Chloris virgata and Echinopilon divaricatum) entered, The ultimate direction of original vegetation succession: Arbor vegetation to tree and shrub and grass to shrub grass.