| The eastern grassland region is an important base of the coal-electricity production in north-eastern China.The long-term coal resource exploitation with high-intensity has exacerbated the contradiction between energy supply and ecological security in this region.Land reclamation has been a necessary measure to alleviate this contradiction.There are two main problems in the process of land reclamation and ecological reconstruction in this area,including the lack of topsoil and poor water holding capacity of the reclaimed soil.To solve these problems,this study investigated the overlying rock and soil layer,and then conduct the research in four aspects.Firstly,the low-cost topsoil alternatives was developed,which has the similar water holding capacity to topsoil,through mixing different proportions of silty loam and sand.Secondly,it deeply analysed the water holding capacity and principles of different layered soil profiles during the water transport process through soil column experiment and Hydrus-1D simulation,moreover the simulation accuracy and reliability of Hydrus model was improved by optimizing the soil hydraulic parameters using GLUE method.Thirdly,to meet the practical needs of the mining area,the soil profile configuration was selected using TOPSIS and grey correlation analysis.The main conclusions are as follows:(1)When the ratio of the silty loam was 40%-70%,the mixed soil would be close to the properties of topsoil in the field capacity,wilting coefficient and available water content.With the increase of the proportion of silt loam,the saturated hydraulic conductivity decreased as a power function.When the ratio of silt loam reached 50% or higher,the decline trend of saturated hydraulic conductivity slowed down and was close to the saturated hydraulic conductivity of topsoil.Therefore,it was recommended mixed soil containing 40%-70% silty loam as a topsoil alternatives in land reclamation,which colud improve the lack of topsoil in study area.(2)Through the soil column experiment,the soil profiles T3 and T4 were similar to the CK during the infiltration process in the wetting front,cumulative infiltration,average infiltration rate,and stable infiltration rate.After 7 days of drainage experiments,T1 profile had the largest total water holding capacity and T2 profile had the smallest total water holding capacity.T2 has the largest topsoil water holding capacity,and T0 has the smallest topsoil water holding capacity.The order of the total water holding capacity of the profiles was T1> CK> T0> T3> T4> T2.The order of the topsoil water holding capacity of the profiles was T2> T3> T4> CK> T1> T0.(3)Under evaporation conditions,the soil profiles T1 and T4 are conducive to water retention.T4 was the largest cumulative evaporation in 30 days,and the water supplied by the lower was also the largest in all soil profiles.T4 can provide water for surface evaporation through upward capillary water.The results showed that topsoil layer of T4 can hold the largest water holding capacity of all profiles after 30 days of evaporation.The soil profiles T2 and T3 were not suitable for soil moisture retention.Due to the nature of the sand layer,their water holding capacity were poor.Although in the drainage process,the sand layer can improve the water holding capacity of the topsoil layer through capillary barrier.However,the water holding capacity of its topsoil layer was not sustainable and will be lost through evaporation in a relatively short period,which was not conducive to vegetation restoration.(4)Optimized hydraulic parameters of layered soil and its posterior distribution were calculated using GLUE algorithm.Excepting for the residual water content,the remaining parameters are sensitive,which have a great influence on the output of the Hydrus-1D model.There is an interactive relationship between sensitive and non-sensitive parameters,as well as hydraulic parameters at different layers through correlation analysis.It indicated that non-sensitive parameters would have an impact on the model output by the sensitive parameters,and it also showed that the layers of soil profile were not independent but interactively influence during the water movement process.There are many hydraulic parameters of layered soil,and the interaction relationship between model parameters is complex.Calibration and verification of Hydrus-1D model was the premise and guarantee for accurately simulating the water movement process.(5)The water holding capacity of the soil profile was evaluated using TOPSIS and grey correlation analysis.Evaluation indicators included average infiltration rate,cumulative infiltration volume,wetting front penetration time,total water holding capacity of 30-day evaporation profile,surface water holding capacity of 30-day evaporation layer,and cumulative evaporation capacity.The weight value of each index was calculated using the entropy weight method,and the weights were ranked from large to small as following: topsoil water retention after 30-days evaporation> total water retention after 30-days evaporation > accumulate infiltration> the penetration time of wetting front > cumulative evaporation> average infiltration rate.Through TOPSIS and grey correlation analysis,it is confirmed that T1 had the best water holding capacity with the highest evaluation coefficient,followed by T4.T0 was closest to the CK in the water holding capacity,but T0 requires a large amount of the topsoil layer,which was not suitable for practical application in the research area with scarce topsoil.Besides,the evaluation coefficients of T2 and T3 were low,which were also unsuitable for soil cover in the study area.According to the above discussion,T1 and T4 were suitable for the soil reconstruction profile in the study area. |
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