| Take the important pilot of water rights conversion——Shenwu irrigation area in the upper reaches of Hetao irrigation area as the research area.In view of the reduction in the irrigation amount from Yellow River,the irrigation quato in the autumn is reduced accordingly,and the water saving transformation of the canal system's anti-seepage effect is enhanced,the problems of redistribution of soil salt and changes in land use types.Combined with 3S technology,the distribution of soil salt and its changing rules on the regional,spatial and time scales were investigated.Grasp the differences in soil salt under different types of land use and evaluate and predict soil salt in detail.It is not only of great significance for the sustainable development of agriculture in Hetao irrigation district,but also provides a certain scientific basis for water resources management,continued construction and water saving transformation,and soil salt control in the irrigation district and surrounding areas.This paper uses regional soil information monitoring,combined with classical statistics,spatial interpolation,buffer analysis,and spatial autocorrelation analysis methods to study the spatial variability,temporal and spatial distribution of soil salt in irrigation districts after water saving transformation,and the differences in soil salt variation in different years of reconstruction.Based on the CART decision tree method,the land use types in the irrigation area were interpreted,and the spatial and temporal changes of soil salt under different land use types were further understood,and the degree of salt deposit in different land types was quantified.Using an effective means of large-scale remote sensing monitoring,combining hyperspectral and Landsat 8 OLI multispectral data to construct a soil salt inversion model,application of CA-Markov model to evaluation and prediction of regional stability and distribution characteristics of soil salt in irrigation areas.The following conclusions are obtained through research:1.After the water saving transformation,the annual average soil salt content in the top soil decreased by 10.67%,and the deep soil increased by 27.12%.The Moran's I index of the two soil layers increased by 6.06%and 32.34%,respectively.During the year,due to the decrease of the irrigation amount from Yellow River,the irrigation quato in the autumn decreased sharply,and the soil salt leaching effect after the fall was reduced by 9.26%.In space,the high value soil salt area(>6g/kg)is mostly located in the Dongfeng sub-canal and the first canal area where the groundwater depth is shallow,and the low-value area(<2g/kg)is located in the southwest and eastern sand areas.From the analysis of LISA agglomeration,it can be known that the Dongfeng sub-canal and the head of a main canal are still the key areas for salinization prevention and control after the transformation.In addition,the radius of the long-term and short-term transformation areas affected by the channel is 1.5km and 0.7km,respectively.The average annual soil salt content of cultivated and deep layers in the buffer zone in the long-term reconstruction zone decreases at a rate of 0.03245g/kg and 0.00282g/kg respectively compared with the short-term reconstruction zone.2.Verify that the CART decision tree interprets the land use type model with high accuracy(overall accuracy>90.00%,use accuracy>80.00%,Kappa coefficient>0.90).Statistical analysis found that the average soil salinity in the cultivated and deep layers from large to small in the three years was saline-alkali land,water body,vegetation,sandy land and others.The average total soil salt deposit in the irrigation area is 884.56t and 531.04t,respectively.Salt deposit per unit of soil decreased by 11.54%,27.46%,and 2.38%,and soil salt deposit per unit of soil increased by 13.11%and 9.83%before spring sowing and during the growth period,and decreased by 1.02%after autumn harvest.The area of sandy land is reduced and the soil salt storage in the cultivated layer is decreasing.Vegetation,water body and saline-alkali land have different soil salt migration at different times.3.Band correlation analysis of hyperspectral and multispectral data(R2>0.800)proves the validity of quantitative inversion of soil salt from multispectral data.Based on the BP neural network,the accuracy of the soil salinity inversion model(R2:0.8751,RPD:2.201)has been greatly improved,which provides a basis for the soil salt inversion in the Hetao irrigation district.Using CA-Markov model(quantity and spatial accuracy>85.00%)to predict the spatial and temporal distribution of soil salt,it was found that the soil salt stable area,salt reduction area,and salt increase area accounted for 2013-2018 respectively.50.04%,42.65%,and 7.32%.The reduction areas are mostly distributed near the sandy land,which indicates that the impact of human activities such as sand drainage canals,water-saving irrigation,and turning waste into wasteland in irrigation areas has led to an increase in salt reduction areas.During the period 2018-2028,the soil salt stabilization area increased by 27.43%compared with 2013-2018,and the increase in the salt reduction area decreased.In addition,the transition probability matrix shows that the probability of conversion from heavy to non-light salt is 2 to 5 times greater than the probability of conversion from non-light to heavy salt.The irrigation and drainage system is desalination,and the type of land use is also an important reason for its change.4.After the implementation of the water saving transformation project,the annual salinity of the soil in the plow layer decreased by 10.67%,the area of the crop growth safe area increased by 6.29%,the surface aggregation was weakened,the irrigation quato in autumn was reduced,and the soil salt leaching effect was reduced by 9.26%.The environment has improved.The land mainly relied on irrigation and drainage system conducts salt removal,and the salt deposit capacity of different types of land use is different.During the year,different types of land use have different dynamics of salt migration.The changes in the spatial pattern of land use types also affect the spatial distribution of salinized soil.It is expected that the salinized stable area will increase by 27.43%from 2018 to 2028.Special salvage areas and chemical modifiers are recommended for specific salinity risk areas. |
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