Processes, Patterns And Reclamation Of Soil Salinization At Manas River Basin, Xinjiang, China

Xinjiang is located in the northwest of China, is a national ecological barrier, fragile ecological environment in most areas, especially native salinization of inland river basin is more common. Manas River Basin is located in the Northern Tianshan Mountains, is one of the most developed economic zones in Xinjiang Province, and is also an important part of eco-fragile zone of northwest arid area. With the development of urban construction and industry and agriculture,there is generate new features in water-salt balance and impact factors because of increasing demand for water, changing land use patterns and water resources allocation, and using water-saving new technology in the region. In this paper, irrigation district of Manas River Basin as the research object, through the background data of many years collected, the combination of different remote sensing images were analyzed soil salinization processes and patterns characteristic of nearly40years in the study area; confirmed the main factors and influencing mechanism of soil salinization by multi-point and long-term monitoring data, estimated the distribution of regional soil profiles salinity combined with EM38electromagnetic induction technology and remote sensing technology, divided water-salt movement type units to irrigation district with natural conditions and human factors, and dynamic forecasting and improvement to representative unit.(1) Based on a lot of collected data, combined1976,1989,1998and2010remote sensing images, arable area of irrigation district was increased from3477.99km2in1976to4868.56km2in2010,70-90s increasing trend, after90years stabilized, woodland, grassland area is different degree of reduction, woodland decreased from674.19km2in1976to489.34km2in2010, lawn nearly40years decreased by nearly70percent, the most dramatic change, land for construction is also showing larger trend of increase, the main reason of soil salinization pattern change is land use type change in Manas River Basin. Surface water was mainly used in water resources development and utilization, the irrigation canal and seepage works at all levels of the active construction after1980years, the new technology of the canal, irrigation reservoirs and shaft irrigation and drainage has been forming after2000. Development of field irrigation and land use change has a greater impact on the water-salt balance and saline soil pattern characteristics, the saline soil mainly in the piedmont alluvial fan, north alluvial plains and low-lying desert region fringes of irrigation district.(2) Landform as a mainly factor that affect soil salinization, the highest soil salt content in the alluvial fan, its surface and bottom were higher than middle layer in the vertical soil profile. Shallow groundwater depth caused by unreasonable irrigation methods and quota, driving on soil salinization of irrigated happen obviously, the coefficient of determination of soil salt content and groundwater depth reaches0.6076. Low salt content in arable, the highest content in wasteland, woodland is higher than grass, soil salinity showed significant higher in surface and bottom than middle in wasteland;1year,3years,5years,8years and10years of farmland planted years longer exhibit lower levels of soil salinity, soil salinity of8years and10years was not significant in each soil layer. When the groundwater table below the critical level, the greater the leaching irrigation quota on soil salinity, on the contrary trend of farmland irrigation and soil salinity in growth period, soil salinity significantly lower after irrigation; within Irrigation most seepage canal, canal also have an impact on soil salinity at a short distance because of most preventing seepage construction.(3) EM38apparent conductivity measured with the salt content of different growth stages and different soil layers are high fitting accuracy, its R2greater than0.8, soil salinity were measured using EM38semivariogram characteristic parameters nugget CO/sill (CO+C) range at2.13%-35.07%in the typical field,0-20cm soil layer mostly moderate spatial autocorrelation, the bottom strong spatial autocorrelation. The characteristics of soil salinity were extracted by hyperspectral technology, good correlation bands with the salt content were483nm,597nm,694nm,815nm,969nm,1373nm,1694nm and1849nm, constructed spectral index SI2and0-80cm soil salt content was significantly correlated, R2is0.71; the spectral index SI2and EM38salt content (0-80cm mean) fit better, best fit equation was Y=0.1082X-6.3946in the typical field, its determination coefficient R2is0.83, combine measured spectral indices with regional remote sensing images to inversion soil salinity, the fitted value R2of remote sensing images inversion and EM38is0.49, reached a significant correlation.(4) Based on the geographical condition and human factors in Manas River Basin, regional water and salt movement type units were divided into strong upward type, weak upward type, up and down relatively balanced type, weak downward type, stable downward type and wind sand types.(5) Strong and weak upward type of regional water and salt movement type units were established BP-ANN prediction and predictive accuracy of the model was evaluated. Using correlation analysis of the factors affecting soil salinity were screened to determine the groundwater depth, monthly evaporation, mineralization of ground water, artificial irrigation and planting years as BP artificial neural network input factors, soil salt content as the output factor, the nonlinear BP neural network prediction model of water and salt dynamic, predictive value and the error value within the allowable range, the prediction accuracy is better.(6) Comparison experiment of different improvement measures on saline soil was carried out in the strong upward movement unit in the study area farmland, from the desalination effects of three years, the first-year results are not satisfactory, the highest desalination rates of salt-isolation to root zone was17.25%, the second-year was significantly improved, the desalination rates of, salt-isolation to root zone, subsurface pipe drainage and chemical improvement were31.24%,64.14%,53.62%and37.61%; salt-isolation to root zone and subsurface pipe drainage measures can significantly reduce soil salinity in0-80cm soil layer, the desalination rate of each soil layer greater than50%, the desalination rates of agricultural measurement was little difference between soil layers, surface desalination was45.42%slightly higher than the bottom; the desalination rates of surface was significantly better than the bottom in the chemical improvement,0-40cm soil desalination rate of55.32%on average.