The Saline-alkali Land Analysis Of Landscape Pattern Evolution And Driving Forces In Songnen Plain

The Songnen Plain is an important food production area in China,and it is also one of the areas where saline-alkali land is concentrated in the world.The increasing area of saline-alkali land has a relatively bad impact on local agricultural production and social development.Therefore,understanding and mastering the temporal and spatial changes of saline-alkali land in Songnen Plain since large-scale human activities and the corresponding driving factors are of great significance for inhibiting the expansion of saline-alkali land.Based on the summary of previous studies,this article focuses on the time span,space span and other issues that existed in the past research,and selecting land use types,digital elevation,and hydrology in the Songnen Plain from 1950 s to 2010s(2018),Weather,water conservancy facilities and other data.Studying the temporal and spatial changes and driving factors of soda saline-alkali land in Songnen Plain since large-scale human development,the main conclusions obtained are as follows:The temporal and spatial changes of the landscape pattern of saline-alkali land in the Songnen Plain show a rapid increase in the early stage,a slow increase in the middle stage,and a gradual decline in the later stage.However,the changes of the saline-alkali land in the Songnen Plain in various provinces,cities and counties have obvious differentiation rules,which are specifically expressed as follows:(1)Judging from the provinces,in the 1950 s,Heilongjiang Province accounted for the highest area of saline-alkali land,reaching about 65% of the total saline-alkali land area of the Songnen Plain,and then rapidly dropped to about 33% in the 1970 s.The change trend in Jilin Province was on the contrary,the proportion of saline-alkali land in Inner Mongolia has not changed significantly;(2)From the perspective of counties and cities,the saline-alkali land of Songnen Plain in each period is mainly concentrated in the hinterland(Baicheng City,Da'an City,Jilin Province,Daqing City,Heilongjiang Province,etc.),and the area of saline-alkali land accounts for The ratio is weakening from the inside to the outside.Since large-scale human activities,the transformation law between saline-alkali land and individual land use types in the Songnen Plain has been differentiated in watershed units.The main channel of Nenjiang-Songhua River,Anzhaoxin River and Huolin River Basin showed a trend of rapid increase in the area of saline-alkali land distribution in the early stage,a slow increase in the middle stage,and a decline in the later stage.The basin has been on the rise.The specific performance is as follows:(1)In the early period,the new saline-alkali land in Taoer River Basin was mainly converted from wetland,dry land and grassland in order of area from large to small,while other watershed was mainly converted from grassland,wetland and dry land.(2)In the mid-term,the new saline-alkali land in Taoer River and Huolin River basins was mainly converted from grassland,while other basins mainly came from water body and wetland.(3)In the later period,the decrease of saline-alkali land area in Songnen Plain was mainly converted into grassland and water body.There were two catchments with different overall changes.Saline-alkali land in Uyur River Basin was mainly converted into dry field,while saline-alkali land area in Taoer River Basin increased mainly from grassland.The temporal and spatial changes of soda saline-alkali land in the Songnen Plain are mainly affected by man-made water conservancy projects and cultivated land,and indirectly affected by climatic effects.The details are as follows:(1)Since 1950 s,the population of the Songnen Plain has increased dramatically,and large-scale development has led to a dramatic increase in the area of cultivated land in the Songnen Plain;(2)Reservoirs and irrigation facilities have been built in the upstream of each river basin for consideration of agricultural production and life safety of residents,and dams of rivers have been built in the downstream,resulting in a lack of river water supply in the downstream low plain areas and a large-scale exposure of saline-alkali land during this period;(3)Dry fields,grasslands,wetlands and lower parts of water bodies in low plain areas are buried with dark alkali layers.Due to drought and water shortage,dark alkali layers gradually move up to the surface and become saline-alkali land;(4)Since 1990 s,the Songnen Plain has begun to construct complete water conservancy engineering facilities such as diversion,irrigation,storage and drainage,introducing surface water of rivers with plenty of water for farmland irrigation,wetland recharge and grassland.Regional saline-alkali land is reversed by irrigation,etc.(5)Regional climate has a fluctuating trend for a long time,which promotes the formation and development of saline-alkali land in the catchment.However,compared with the construction of water conservancy projects,climate is only a secondary factor.