Comprehensive Assessment Of The Impact Of Land Withdrawal And Water Reduction Of The Eighth Division Of The Corps On Water And Soil Resources Under The Condition Of "Three Red Lines"

Object:The eighth division of the Corps is located in the northwest hinterland of Xinjiang,China,and is short of water resources.The region is dominated by agricultural production,and the"three red lines"of water resources constrain the region to gradually implement the measures of land withdrawal and water reduction,resulting in new problems of water and soil resources matching and soil quality degradation after land abandonment.In order to ensure the sustainable use of regional water resources and the protection of soil quality,this thesis comprehensively evaluated the impact of the"three red lines"on the regional water and soil resources,which has important theoretical and practical significance for the sustainable use of water resources and the sustainable development of ecology,society and economy in the Eighth Division.Methods:The balance model of water resources supply and demand in the Eighth Division is constructed by using the index analysis method;The soil quality index method and the modified Nemero index method were used to evaluate the soil quality of returning farmland;Finally,based on the"social benefit-economic benefit-ecological benefit",the comprehensive benefit model of water resources is constructed,the comprehensive weight is determined by AHP-CRITIC method,and the TOPSIS model and VIKOR model are selected to evaluate the comprehensive benefit of water resources.Results:(1)Total regional water demand in the base year is 1.313 billion m3,Remaining water is 10.6928million m3;The total regional water demand in 2025 will be 1.306 billion m~3,and the total water demand will exceed the water consumption index by 7%.The irrigation quota in 2025 will be 247.47 m~3/mu,and347000 mu of arable land will need to be reduced or rotated to meet the balance between supply and demand;The total regional water demand in 2030 is 1.289 billion m~3,which exceeds the water consumption index of173.8604 million m3,and the irrigation quota in 2030 is 244.47 m~3/mu.It is necessary to reduce or rotate535700 mu of farmland to meet the balance between supply and dem.(2)Both the farmland conversion plot(RF)and the adjacent farmland plot(CK)are moderately saline soil.The salt content of RF treatment is 10.84%higher than that of CK treatment,and the salt content accumulates after farmland conversion.The soil nutrients of the two treatments have"surface accumulation"phenomenon in the vertical direction,and the soil nutrients of RF treatment are lower than that of CK treatment.According to the statistical characteristic value of soil fertility index,the modified Nemero index method was determined to be more suitable for the study area.The modified Nemero index method showed that the fertility level of the two treatments were lower than the middle(III).The comprehensive index method of soil quality and the modified Nemero index method have the same evaluation on the results of soil fertility change with the soil layer,both of which are that the soil fertility index of CK treatment is higher than that of RF treatment,and the soil fertility of RF treatment 0～60 cm soil layer decreases sharply with the depth,and the soil fertility of 60～100 cm soil layer basically does not change;There was a negative correlation between soil fertility and depth in 0～100cm soil layer treated with CK;The soil fertility index of40～60 cm soil layer has the largest difference,and the soil fertility index of the modified Nemero index method has a difference of 0.08,and the deep soil degradation is serious.(3)TOPSIS model and VIKOR model have the same evaluation results on the comprehensive benefits of water resources in the region from 2011 to 2020,both of which show that the comprehensive benefits of water resources in the region from 2011 to 2013 are poor,below Level III(medium),around Level II(good)from 2014 to 2017,and Level III(medium)from 2018 to 2020;The overall change law of the comprehensive evaluation value of water resources is also consistent,showing an upward trend from 2013 to 2015,a downward trend from 2015 to 2018,and an upward trend from 2018 to 2020.The results of the two models can support each other and have good practicability.The comprehensive benefits of water resources in the region have gradually increased since 2018,indicating that the utilization of water resources in the Eighth Division is developing in an orderly and coordinated way.Conclusion:After 2018,the utilization of water resources in the Eighth Division has improved,and the comprehensive benefits have increased year by year.However,the supply and demand of water resources in2025 and 2030 are still unbalanced.It is necessary to continue to carry out effective management of water resources to make the utilization of water resources develop in an efficient direction.After the implementation of land withdrawal and water reduction,the soil quality of the land to be reclaimed has decreased significantly.In order to prevent land desertification,it is necessary to protect the land to be reclaimed.