Change And Forecast Of Farmland Water-salt Environment After Water Saving Reform Implemented For Salinity Region

To the question of Chinese large irrigation area:available water is reduced; effective irrigation area ratio is low; engineering services is old; efficiency of irrigated water is low. Since1998, the country started water saving reform and irrigation district reconstruction project, however, when improving the condition of irrigation, improving the irrigation agricultural comprehensive production capacity, farmland rule of hydrologic cycle in irrigation area is changed. The improving of canal lining、field water-saving and conjunctive use of canal and well technique breaks intrinsic farmland water salt dynamic balance, what take farmland water salt balance and farmland water-environment to change. How will the changing impact irrigation agricultural development, which becomes the focuses of attention. For the above problems, against the background of water saving reform project implementation in the northern large-scale irrigation districts, cold-dry Hetao irrigation area of Inner Mongolia in north China is taken as research, the paper discuss the impact on the irrigation area of water saving reform from groundwater chemistry、soil salinity profile type and its distribution characteristics、groundwater depth and the relationship between soil water and salt and groundwater.1. The groundwater samples in Hetao irrigation area of Inner Mongolia are analyzed scientifically and systemically. then the descriptive statistics, the correlation matrices, the ratio coefficient of the main ions and the graphical method(H. HToJicTHXHHr diagram、the piper diagram and Multi-rectangular diagram are applied to Hetao irrigation area) are used to gain the better understanding of the spatial and the temporal variation of the hydrochemistry characteristics and the evolution laws of groundwater in Hetao irrigation area of Inner Mongolia. The followingmain hydro chemical processes are inferred to controll thewater quality of the groundwater system in Hetao irrigation area of Inner Mongolia at earlier stage and later stage of water saving reform:(1)the weather-dissolution,(2)the evaporative condensation,(3)the ion-exchange reactions, and (4)the mixing of the surface waterwith high salinity. The paper come to the conclusion that after water-saving rehabilitation, bicarbonate ion concentration increase, chloride ion concentration and sodium ion concentration decrease: After water saving reform implemented, the bicarbonate ion become the main cation of groundwater; After water saving reform implemented, the groundwater of the irrigation area is freshening, and its harm for crop weaken; Chemical types that the bicarbonate ion is in leading position are more.Seven kinds of irrigation methods used at home and abroad are applied to evaluate the groundwater quality in Hetao irrigation area of Inner Mongolia at earlier stage and later stage of water saving reform. The paper analyse trends in the groundwater quality and come to the the conclusion that groundwater quality is freshening.The paper establish chemical classification of groundwater model based on Bayes discriminant analysis method, provide the new quantification way for evaluation and classification of chemical classification of groundwate in Hetao irrigation area2. The study is supported by GIS technology. Geostatistic、the cluster analysis、the descriptive statistics and the accumulation coefficient are used synthetically. Characteristics and regularity of spatial, horizontal and vertical, distribution of soil EC in different salinity profile types on the middle and lower reaches of Hetao irrigation area of Inner Mongolia at earlier stage and later stage of water saving reform were studied and summarized scientifically, and these regularitieswere then used to explore spatial distribution of different salinity profile type. The paper reveals difference from distribution of soil EC in different salinity profile types and spatial distribution of different salinity profile type at earlier stage and later stage of water saving reform, meanwhile offers scientific support for fall irrigation. Soil salinity profile on the middle and lower reaches of Hetao irrigation area could be obviously classified into normal and even. According to the similarity of different soil layers, a soil profile of100cm in depth in upriver and middle reaches area could be divided into two layers,0～20cm,20～100cm:a soil profile of100cm in depth in lower reaches area be divided into two layers,0～40cm,40～100cm. Compared with the distribution of salinity profile types on the middle and lower reaches of Hetao irrigation area of Inner Mongolia at earlier stage and later stage of water saving reform, salinity profile types are toward the even, and the soil salinity reduce integrally, after water saving reform implemented.3. Using stochastic theory, the prediction of groundwater depth Model Based on Markov Chain with weights was established.The paper introduce memberships and leveled characteristic value of fuzzy set theory into establishment of model, that realized forecast of detailed groundwater depth value, increased function of the model Markov Chain with weights. Using ergodic theorem, the paper forecast the intervalvalue what groundwater depth locate on the middle and lower reaches of Hetao irrigation area of Inner Mongolia, and point out the key control area of groundwater depth in Hetao irrigation area of Inner Mongolia in the future. More Often, the groundwater depth in middle reaches area is between2.380and2.742, and the groundwater depth in lower reaches area is between 2.218and2.506. The value of interval is under critical buried depth of groundwater in Hetao irrigation area of Inner Mongolia (2.0m). In the future, the soil Salinization in middle and lower reaches area is alleviated possibly. But more often, the groundater depth in upriver area is between1.227and1.727, In the future, The lower reaches area of Hetao irrigation area of Inner Mongolia is key area that is controled.4. In LinHe area of Hetao irrigation area of Inner Mongolia Case, the paper discussed the relation between soil water and salt and groundwater after water saving reform implemented, analysed the changing regularity of mineralization in one year, reveals the impact on the soil water content of groundwater under the different depth level, and the relationship between groundwater depth and soil salt content under the conditions that is the mineralization is same. The paper come to the conclusion that groundater effects have an effect on soil volume moisture content of100cm in depth, and the influence on soil volume moisture content of60-100cm soil layer is more.with the change of groundater depth level, the soil volume moisture content of100cm in depth decreased gradually.with the hydrological year (humid year—drought year—Special drought year) under the condition that groundwater depth was deep, soil volume moisture content increased gradually. Under the condition that Groundwater salinity was unchanged basically, the relationship between soil conductivity of root layer and groundwater depth was exponential relationship. To0～20cm%20～40cm and40～60cm, groundater depth have the biggest effect on salt of topsoil (0～20cm). salt contentof surface soil (0～20cm) was the most sensitive to the change of Groundwater salinity.