| Soil salinization,as an important environmental disaster,is an important cause of soil degradation and brings huge losses to human production activities and ecological environment.China's northwestern region is rich in land resources and has sufficient light and heat conditions.With the implementation of the western development strategy,Gansu Province invested in the construction of Jingtai high lift irrigation project,which caused serious soil salinization due to unreasonable irrigation methods.In this study,9 remote sensing images of the Jingdian Irrigation District in 1976-2018were selected,and classified the salinized soil by visual interpretation and supervised classification.Carry out classification post-processing and accuracy evaluation.By classifying the salinization of different typical terrain areas in the first and second stage projects of Jingdian Irrigation District,the spatial distribution and area change of each type of salinization,the changing trend of soil salinization and its changing rate are obtained.The main driving factors of soil salinization in typical areas were discussed.The main conclusions as follows:(1)In recent 42 years,salinization in Jingdian Irrigation area showed an aggravating trend,and the total area of saline-alkali land increased significantly.The soil area of each type of salinization changed greatly.By 2018,the total area of saline-alkali land is 112.97 km~2,which is mainly moderate saline-alkali land and heavy saline-alkali land,the proportions are 25.57%and 34.61%respectively.The change dynamic degree of extremely severe saline-alkali land was higher than that of other saline-alkali land,mainly for the transfer of heavy saline-alkali land and moderate saline-alkali land.(2)The light saline-alkali land and moderate saline-alkali land in the first-stage irrigation area are mainly distributed in the Sitan-Luyang Basin and the Caowotan Basin.The proportion of light saline-alkali land area in the early stage of the project is large and the area reached the largest in 2009.From 1976 to 2009,it expanded to the west of the Luyang Basin and the northern and western parts of the Caowotan Basin,and the area gradually decreased in 2009-2018.The formation of severe saline-alkali land in the Luyang Basin and the Caowotan Basin was relatively late,and its area increased first and then decreased.The center of gravity extends to the west and north of the Luyang Basin and the western and northern part of the Caowotan Basin.In 2009,the heavy saline-alkali land disappeared in the Luyang Basin,and the degree of salinization in the Caowotan Basin weakened.(3)The extremely heavy saline-alkali land is mainly distributed in Caowotan basin and Baidunzi basin.Among them,the Caowotan Basin has a small area,and the area reached a maximum of 0.87 km~2 in 2009.The change trend of extremely heavy saline-alkali land in the closed-type Baidunzi basin is obvious,showing a continuous increasing trend,and the change dynamic degree is the largest in 1995-2000,which is37.8 percent.The area of extremely heavy saline-alkali land changed slightly in2009-2018.The results showed that the area restricted by terrain factors increased less,but the salinization degree deepened with the accumulation of salt.Due to the occlusion of the topography of the Baidunzi Basin,the continuous accumulation of groundwater has led to a deepening of soil salinization.The area of moderate saline-alkali land transfer to heavy saline-alkali land and extremely heavy saline-alkali land is large,and the severity of the severe saline-alkali land is decreasing to the west and the area is increasing westward.(4)Both natural and human factors act on the temporal and spatial evolution of soil salinization in irrigated areas.The natural factors are mainly due to the rise of air temperature,which promotes the development of soil salinization.Large-scale land development and utilization by humans in irrigation districts and unreasonable irrigation methods are external factors that lead to increased soil salinization. |
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