Eco-hydrological Effects Of Clay Sand Barrier In Minqin Oasis Fringe

It is a debated problem with so much academic concerns all along that how soil crusts affect on the soil hydrological process and the growth of the plant distrubtion. This paper synthetically analyzed the effect and mechanisms of soil crusts with different development on soil hydrological processes through a series of field ecological investigation on soil crusts, experimental analysis on soil crusts’ hydrological properties, as well as dynamic monitoring to soil water content after natural and simulated precipitation; preliminaryly summerized the succession rule of desertvegetation ecosystem with soil crusts of different develpoments combined with the growth status and species diversity of vegetation in different sandfixing areas. The primary conclusions were as follows:(1) In recent 50 years, the average annual precipitation in Oasis fringe of Minqin is 115.6mm, and the monthly distribution vary widely. The local rainy season concentrated in June to September, accounting for 73.92% of annual precipitation. According to the distribution of rainfall in recent 10 years, the rainfall frequency of the level of 0.1~5.0mm and 5.0~10.0mm are the top two, respectivly accounting for 81.9% and 12.6% of the number of annual rainfail. For the precipitation more than 10 mm, the frequency is less than 5%, while the proportion accounting for 35.1% of annual rainfall. From the view of precipitation intensity and capacity, the rainfall in MinQin can be divided in to the weak precipitation intensity but strong capacity and strong precipitation intensity but weak capacity.(2) Soil crust at the artificial sand-fixing vegetation areas of Minqin Oasis can be divided into biological and physical crust, in which the crust of early 1960 s, mid 1960 s and 1970 s are mainly biological crust, however the crust of 1980 s, 1990 s and 2000 s are mainly physical crust. According to the analysis of physical and chemical properties of soil crust, its thickness, tightness, clay and silt content, organic matter, total nitrogen content increases with the increasing of the sand-fixing age, but the impact on the density are on the contrary.(3)The precipitation interception caused by crust layer and 2-10 cm soil layer are different. The precipitation interception caused by crust layer and sand-fixing age are positively correlated(r = 0.961), and the longer of the crust developmental age is, its influence on the precipitation interception and water movement in the soil are greater. The precipitation interception caused by 2-10 cm soil layer under the coverage of biological crust decreases with the increasing of the sand-fixing age, but under the coverage of physical crust is vice versa.(4)According to the continuous observation of 28.4mm natural precipitation, the crust can indeed lead to soil water redistribution toward top layer. With the increasing of the sand-fixing age, the precipitation infiltration depth showed that early 1960 s < mid 1960 s < 1970 s < 1980 s < 1990 s < early 21 st. Under the condition of weak precipitation intensity but strong capacity, the infiltration depth decreases with the increasing of the sand-fixing age, however Under the condition of strong precipitation intensity but weak capacity, the infiltration depth increases with the increasing of the sand-fixing age. The performance of the impeding effect of infiltration caused by crust of diffrent ages shows that 1960s> 1970s> 1980 s, and impeding effect deteriorated with the increasing of the precipitation capacity.(5) The impact of crust on the soil moisture redistribution has differences and stages. At the stage of mainly soil water infiltration, soil moisture redistribution of 0-10 cm and 10-20 cm layer increases with the increasing of the sand-fixing age. At the stage of infiltration-evaporation stage, moisture difference of 0-10 cm and 10-20 cm layer decreases. Considering 0-10 cm layer, setting the 1980 s as the boundary, biological crust moisture redistribution increases with the increasing of the sand-fixing age, but the physical crust moisture are on the contrary. At the stage of mainly evaporate, soil moisture of 10-20 cm layer is higher than that of 0-10 cm layer, and the moisture content of both decrease to both sides of the the 1980 s.(6) Different types of crust have different effects on evaporation. After precipitation of 28.4mm, physical crust perform a single promoting role on evaporation, but biological crust show to restrain first and then promote. The age gradient of soil crust evaporation only performance on the cumulative evaporation, which increases with the increasing of the sand-fixing age. Over time, the evaporation process of each era tends to slow down, but the age gradient of cumulative evaporation have larger diffrence, and the overall performance show that biological crust> quicksand> physical crust.(7) The height, diameter and breath of Halxylon ammodendron of different ages are all increases with the increasing of the sand-fixing age, but the new length are on the contrary. The density and coverage of Halxylon ammodendron have both been plunged in the 1980 s, but herbaceous diversity reach the highest. The number of species per unit area, vegetation cover and diversity index shows that fixed sand vegetation(1960s, 1970s)> semi-fixed semi-mobile sand vegetation(1980s, 1990 s, early 21st)> mobile sand vegetation. The appearance of Eragrostis pilosa, Limonium aureum and other evidence plant also indicates that the soil moisture conditions has been improved.