Dynamic Change And Prediction Of Soil Water Of Dunes Paving Eco-mat At Eco-tone Between Oasis And Desert

The soil moisture is regarded as a key factor of the SPAC; it not only influences the characteristics of the soil and the growth of the plants directly, but also influences the distribution of plants and the changes of the local conditions to a certain extent indirectly.With the development of the vegetation in harnessing sand, soil moisture of sand dune appears obviously downward trend; moisture enough becomes the most baffles.The whole system has presented an unstable phenomenon, and the vegetation becomes weak ahead of time.So, the soil moisture state is the important condition of the success or failure in the vegetation recovery and controlling sands.It is the key point of fixing the sand for a long time and the vegetation restoration that taking measures to raise the content of the soil moisture and improve the utilization ratio of the limited precipitation, and it is of very important realistic meaning.The eco-tone between oasis and desert is an important zone for vegetation restoration. The key for vegetation restoration is to know the soil water content of dune.In this study, the temporal and spatial variation of soil water content in sand dunes in Zhangye City was measured continuously from October in 2004 to October in 2005, and the application of eco-mat to combating desertification was studied initially.The main research results as following:1. The eco-mat could inhibit soil water evaporation in sunny days and reduce precipitation infiltration in rainy days, so it could reduce spatial variability of soil water (CV=4.61%).Soil water content of mobile sand dune in 0~40cm (1.19%~1.27%) was lower than that of fixed dune (1.61%~1.75%), while under the 40cm layer, the case was reversed. Soil water content of mobile dune (1.27%~1.73%) reduced from the top to the bottom of sand dune profile, while for fixed sand dune (1.75%~1.11%), the case was reversed. The main reason was that there was sparse vegetation canopy, strong wind and large disturbance on the surface of mobile sand dune, while the fixed sand dune's crusts decreased soil water evaporation and its developed plant roots consumed the soil water of deep layer of the sand dune.2. By using standard deviation and variation coefficient, the vertical layers of soil water content were divided into three layers, i.e., rapid change layer, relative stable layer and stable layer, respectively. The division of profile layers had relationship to the types of dunes and sand-fixing models, and the different layers had different characteristics.3. Correlation analysis was applied to analyze the relationship of soil water content among different layers and coefficients of soil water content and means of all layers under eco-mat condition.The study showed that the soil water content of upper layer has the most closed relationship with that of middle layer, while with the barrier function of eco-mat, the soil water content of upper layer has weak correlation with that of deep layer. The correlation of soil water content between middle layer and upper layer was closer than that of deep layer, and the one between deep layer and middle layer was closer than that of upper layer.4. The dynamic variation of soil water content was affected by the precipitation, vegetation, surface coverage and so on.The monthly change of soil water content lagged behind the precipitation, and it's mainly because the vegetation, surface canopy, crusts and plant roots limited the soil water infiltration.5. Using eco-mat to control mobile sand dune effectively reduced soil temperature of the soil layer from 0cm to10cm, and slowed down variation amplitude of soil temperature, which was benefit to reduce soil evaporation in high temperature.6. On the basis of dynamic simulating and forecasting the soil moisture content with the methods of the exponent smooth and self-regression model, some conclusions as follow: the modeling precision of exponent smooth model was higher than that of self-regression model, but the forecasting precision of self-regression model was higher than that of exponent smooth. All in all, for the dynamic simulating and forecasting the soil moisture content, we should take different models.By and large, ecological mat, a new kind of environment protective material, not only didn't lead to environment pollution, but could improve the soil water condition of sand dunes. For ecological mat, it was a slow course to decompose in the arid area of north China, especially in the desert region.In the process of studying, the eco-mat on the sand dunes hadn't decomposed, but it had played very outstanding roles in preventing wind erosion, improving the condition of soil moisture and temperature of sand dunes. After covering eco-mat, soil water was departed from exchanging with the atmosphere, and further lead to the internal water circulation and changed the distribution of soil water.Therefore, the results of this research have been showed that in the process of sand fixation and vegetation restoration, the eco-mat could maintain soil water content of dunes effectively, create good conditions for the growth of sand-fixing plant and improve the vegetation surviving rate. So, it provided a new model of desertification combating.