A Study Of The Vadose Zone Water Movement’s Law Under The Influence Of Vegetation

Mu Us Sandland is one of the twelve sandy areas in China, across Shaanxiprovince, Ningxia and Inner Mongolia autonomous regions. It covers NorthernShaanxi energy and chemical base and Inner Mongolia energy base. With theconstruction and development of the energy base, water demand is increasing, andwater shortage becomes a bottleneck, which restricts the local economic and socialdevelopment and energy bases.Because of drought, water shortage and a fragileecological environment in this Region, ecological environment highly depends onwater, especially depends on the vadose zone moisture and groundwater, Therefore,we urgently need to strengthen the study of the groundwater resources developmentand the coordinated development between socio-economic and ecologicalenvironment, it is a great significance to assess the groundwater resources in Mu UsSandland and protect ecological environment.On the basis of summarizing and analyzing the previous results, through fieldinvestigation, in situ tests, the root sample collection, test data analysis and numericalsimulation, I systematically analysis the relationship of the non-exposed and exposedareas of the region’s typical vegetation profile between the vadose zone moisture toobtain the following results and knowledge:1, According to the test analysis, from the point of view the profile of the typicalvegetation of Korshinsk Peashrub, Artemisia and Salix, weather conditions andvegetation root affect the space distribution of the vadose zone moisture, especiallyrestrict the water migration of soil surface0~60cm above, which makes the spatialand temporal distribution’s similarities and differences of the soil moisture contentbetween exposed areas and non-exposed areas of the different vegetation profiles.2, Through the variation characteristics’ analysis of the soil moisture profiles ofthe exposed area and non-exposed areas of the three vegetations, we obtain that soilmoisturel on the exposed and non-exposed areas of different vegetation profiles in the vertica is basically divided into three layers: Ⅰ rapidly changing layer, II smoothlayer and III slowly changing layer, but hierarchical position is different. The Contrastdegree of the soil moisture content’s differences is: Korshinsk Peashrub profile> Salixprofile> Artemisia profile. Korshinsk Peashrub has a large impact on the change ofsoil moisture content in the study area, followed by Salix, Artemisia minimum.3, By analyzing and sorting the vertical one-dimensional total water potential lawof the three vegetations, we obtain: below80cm in depth, Each profile of the totalwater potential trend is the same, I(θ)≈1, Basically it can be divided into2belts,respectively, is the atmosphere-soil moisture active exchange belt and the watertransition change belt, but different vegetations have certain differences of the belts onthe different depths. Different vegetation profiles’ zero flux plane distributions are notthe same at different times, different depths, especially above the soil70cm. Therelationship of the total water potential more frequently change is: Artemisia profile>Korshinsk Peashrub profile> Salix profile. Artemisia has a large impact on the vadosezone vertical water distribution in the study area, followed by Korshinsk Peashrub,Salix minimum.4, Respectively sample Salix profile roots on interdune depressions and sanddunes of the two different landforms by the mining law, and analyse Salix roots’effective root weight and root length in non-exposed areas, sum up the distributionlaw of Salix roots:The distribution of Salix roots in the different landforms have somedifferences, Salix roots on interdune depressions distribute as "inverted triangle",mainly using the shallow water in the depth of0~60cm underground; Salix roots onsand dune distribute as gourd-shaped, not only using the accumulation of soil surfacemoisture, but also mainly using the water in the depth of80~120cm underground.Salix root length density and root weight density are positively correlated, root length,root weight density distribution and soil moisture are negatively correlated.5, Establish vadose zone water transport model about salix profile under theinfluence of vegetation at different landforms by HYDRUS-1D software, fit theprofile’s moisture content and total water potential in the identification period and validation period, the errors are in the error limit, the macro effect is better to lay thefoundation for the quantitative calculation of Salix root water absorption.6, This paper uses the finite difference principle to calculate vegetation rootwater uptake rate of the Salix profile on non-exposed areas under different landforms,the results show that the root always grow to the areas which have sufficient waterand most likely to absorb moisture, when surface water is reducing, root grows intothe lower, water absorption rate increases in the lower; when surface water is enough,the Salix root water-uptake peak goes back to the upper soil.In the vertical partition,the root water-uptake rate of Salix profile’s non-exposed areas on interdunedepressions is divided into: I, root water-uptake is strong(0~40cm); II, rootwater-uptake is slow (40~80cm); III, root water-uptake is weak (80~120cm). Theroot water-uptake rate of Salix profile’s non-exposed areas on dune sand is dividedinto: I, root water-uptake is strong (0~30;70~120cm); II, root water uptake is slow(30~70cm).7, Calculating the Salix evaporation and transpiration using the amendedPenman-Monteith formula which is recommended by FAO, the results showed that:Salix evaporation and transpiration are mainly concentrated in the calculation of the100to150days,that is mid-July to mid-August. From the evaporation andtranspiration point of view, the Salix evaporation and transpiration in interdunedepressions is greater than in the dune sand, which shows that the transpiration ofSalix is showing a weakening trend from the interdune depressions to the dune sand.