Study On The Transport Of Soil Water And Salt

Soil salinization and desertification are the major types of land degradation inChina.Soil salinization is usually appear in the soil evaporation intensity big, dry littlerain, high underground water level and area containing a higher proportion of solublesalts. Soil salinization is the result of a particular climate, topography, geomorphology,hydrogeology and other natural factors produced.Soil salinization harm is serious, notonly easy to cause the destruction of land resources and waste, cause huge losses toagricultural production and development of oases in arid areas, but also to the oasisstability constitute a great threat to the survival of humans.Therefore, soil salinizationoases in arid areas is always related to the quality of ecological environment in aridareas and the sustainable development of the important problems.The current remote sensing is widely used in monitoring of soil salinization,remote sensing technology can read fast and efficient to get salinization changeinformation, but its drawbacks are the use of remote sensing images only directextraction salted characteristics of information, lack of consideration of salinizationmechanism, it is difficult to salinity changes in a more accurate simulation forecasts.Solute transport model for monitoring soil salinization salinization can occur from thestarting principle, the use of mathematical modeling approach to soil salinizationtracking simulation case study area, high simulation accuracy, but the the dataacquisition is more complicated, we need for a large number of laboratoryexperiments.So it always have a smaller scale studies. And generally the studies aresmall-scale farm or a specific test site. Remote sensing and solute transport modelcombining both from salinization mechanism to explain its occurrence and developmentof numerical simulation, but also for large-scale information extraction to its tendencyto expand the research scale, multi-source data assimilation lay foundation.In the Oasis of arid areas, develop the remote sensing technology based on regional water and salt migration change process simulation and prediction research, quantitativedescription of salt and water movement law, provide the basis for forecast and preventsoil salinization, is of great significance in the study of soil salinization in aridareas.Taking WeiGanRiver-kuqa river oasis as the study area, with Landsat8images asdata sources, to salinization information extraction in the study area, the mild salineland, moderate in brine, heavy saline soil samples of indoor experiments, measured themoisture movement parameters including soil water characteristic curve, andunsaturated hydraulic conductivity of soil K (θ), unsaturated soil water diffusivity D(θ);Solute transport model for computing the parameters of the hydrodynamicdispersion coefficient D (v, θ), in the study area meteorological data, measured data onthe basis of underground water level and so on, using the HYDRUS model for the studyarea on September3,2013to December9,2013, to simulate the water salt dynamic lawcarries on the discussion on the development of the oasis area salinization, oasis forevaluation and improvement of soil salinization and soil secondary salinizationprevention and control, provide certain theory reference and scientific basis.Mainly withthe following conclusion:(1) the use of remote sensing images in the study area, the image of the normalizeddifference vegetation index (NDVI), improved normalized difference water index(MWDWI) is extracted, K-L transform for image reflectance, combined with sand andsevere salinization in the studied area is relatively sensitive Band7band and Band2blueband, using decision tree classification method, to extract information of salinization inthe study area are classified, classification accuracy is higher.(2) the solute transport parameters of soil samples in the studied area, the soilmoisture feature curve, soil water diffusivity, hydrodynamic dispersion coefficient ofunsaturated soil hydraulic conductivity, etc were determined.Soil water characteristiccurve using the actual test data using the Van Genuchte RETC software to fitting, getsoil saturated θr θs, soil residual moisture content, soil water characteristic curve and other parameters in the shape of alpha, n, m, etc.;Unsaturated soil water diffusivityusing experiment data obtained by exponential fitting test;Unsaturated soil hydraulicconductivity by using mathematical method of soil water characteristic curve iscombined with the special mathematical relationship between the bulk density thanwater has been saturated theta s, soil residual moisture content, alpha, theta r n, m) data.(3) of salt and water movement of the current theory, the development of water andsalt migration model are summarized.The HYDRUS model software development,application and development course, software modules made detailed instructions,applicable conditions, etc.: the basis of numerical simulation of the model of soil watermovement equation and the soil solute transport equation, has carried on the detailedexplanation, on the model of the formula is derived.(4) according to the characteristicsof the study area to define the initial conditions and boundary conditions of thesimulation, using the simulated prediction model, the output of the correspondingsimulation results, the test and numerical simulation results using the site.The resultsshow that the HYDRUS model can better simulate the soil moisture content and salinitydata in the study area in vertical scope change in trend, reflects the soil water and saltchange rule in the study area, water and salt monitoring of oasis is practical, as toprovide theoretical basis for salinization assessment and prevention and control of oasesin arid areas.