Study On Soil Hydrology Effect Of Vegetation Restoration In Dump Of Open Pit Coal Mining

Coal mining will destroy land resources,especially in open pit mining.Dump,which is formed in the open pit mining platform-the slope of the pagoda-like giant artificial loose accumulation,has destroyed the vegetation and the natural of hydrology,geology and geomorphology conditions.Dump has a poorly structured or unstructured soil,a large number of soil macropore,and prone to soil preferential flow of precipitation infiltration.These processes can affect soil moisture utilization efficiency and the formation of rapid water migration channel may be to a certain extent,induced collapse,landslides and other soil erosion.Dump is the most serious areas of soil erosion in the industrial and mining areas.How to quickly restore vegetation is the primary problem facing the reclamation of the dump.In the past,the study on the vegetation restoration mainly focused on the selection of plant species and their adaptability and ecological reconstruction and restoration.The degree of vegetation restoration from the perspective of soil hydrological effect is also limited to the general comparison soil property index,the evaluation index system of soil hydrological effect has not been established and the systematic research is lack.This paper taking Robinia pseudoacacia land,Ulmus pumila land,mixed forests land,shrub land,farmland and weeds land of dump reclamation area of Haizhou open pit coal mine in Fuxin City,Liaoning Province as the research object and through field investigation,field test and indoor analysis,and the characteristics of litter layer hydrological,root distribution,soil water physical properties,infiltration characteristics and their influencing factors under different vegetation restoration modes were obtained.The range and density of soil macropores were obtained by soil water breakthrough curve and the main influencing factors of soil macropores distribution were determined.Taking the method of brilliant blue staining solution tracer test,the morphological characteristics and changing regularity of soil preferential flow under different vegetation restoration modes were studied.For the first time from the perspective of soil preferential flow,the environmental factors,which were most relevant with soil preferential flow area,such as soil factors?total porosity,capillary porosity,soil macropores radius,gravel content,clay content,the proportion sand and silt content?,water factors?Soil water content and saturated hydraulic conductivity?,vegetation factors?root weight density,<1 mm,1² mm,2⁵ mm root length density?,has been used as soil hydrological effect evaluation index of dump vegetation restoration.Using the AHP method,a reasonable evaluation index system of soil hydrological effect was established and quantitative evaluation,and the best model of vegetation restoration was selected.The main conclusions of the study are as follows:?1?The range of diameter at breast height,tree height and crown width in Robinia pseudoacacia land,Ulmus pumila land,mixed forests land are 4.03⁶.53 cm?4.62⁶.14 m?1.95³.92 m and there are various kinds of herbaceous plants in 2⁶ species.The plant root under different vegetation restoration models was concentrated in 0-40 cm,the root length accounted for 95.1%,93.55%,92.21%and 95.1%of the total length of the root system in Robinia pseudoacacia land,Ulmus pumila land,shrub land and weeds land.?2?The litter thickness and litter accumulation of forest land was larger than the grassland,and different vegetation restoration models were mainly in the non decomposition layer,and the reserves were 1.68².08 times of the decomposition layer.The natural moisture content,m aximum water holding rate and maximum water holding capacity of litter between decomposition and decomposition layers was significantly different.The maximum water holding rate of litter is between 155.58%and 206.58%.Litter interception rates between the119.74%¹66.05%,effective retaining content between the 10.84⁹8.76 t·hm^-2,were showed strongest impoundment ability for Robinia pseudoacacia woodland.The water holding capacity of the litter under different vegetation restoration models decreased with the time increasing,the change range was 1414.85²247.41 g·kg^-1.The water holding capacity and water absorption rate under different vegetation restoration models were all higher than those of the non decomposition layer,which showed that the forest land was more than the grassland;The fitting results of water absorption rate of each sample were better than that of the time with power function(V=at^-b),and the coefficient of determination of R² was above0.99.?3?The soil bulk density under different vegetation restoration models is farmland>weeds>forest land.Soil porosity is dominated by capillary porosity and the value is24.41%⁵0.92%;Soil relative water content in different soil layers is difficult to effect water and soil moisture in the soil dump is difficult to be absorbed and utilized by vegetation.There are different levels of water deficit of each plot with 0⁶0cm soil layer during the observation period.The saturated soil water storage capacity and the maximum water storage capacity of the surface soil of forest land were more than that of grassland,while the maximum retained water storage capacity was higher than that of forest land.The total amount of gravels under different vegetation restoration models in dump increased with soil depth and the mean content of total gravels in soil profile was the lowest in farmland;In terms of relative mean content of gravels by particle size,the gravels in the dump exhibited an order of?2¹0 mm?>?>20 mm?>?10²0 mm?.There was a significant logarithm correlation between soil saturated water storage and>2 mm gravel content?p<0.05?,a significant linear correlation between2¹0 mm gravel content?p<0.01?,and a significant parabolic correlation between 10²0 mm gravel content?p<0.05?.?4?The stable infiltration rate under different vegetation restoration models in the order of Robinia pseudoacacia land>Ulmus pumila land>mixed forests land>shrub land>farmland>weeds land,its value between 0.2⁵.1 mm·min^-1.Infiltration regression model fitting goodness as Horton model>Kastiakov model>G-P integrated model.There was a closely related between soil infiltration performance and non-capillary porosity,gravel content,root length density,and root surface density.Soil infiltration capacity of dump with different vegetation restoration models is Robinia pseudoacacia land>Ulmus pumila land>mixed forests land>shrub land>farmland>weeds land.?5?The characteristic of water breakthrough curve under different vegetation restoration models differed significantly and the steady effluent rate of surface soil layer was0.0193⁰.0315 mm·s^-1,which was 6.35¹0.22 times of 50⁶0 cm soil layer.The steady effluent rate of arbor forest was higher than shrub land and weeds.The water breakthrough curve showed a trend of increasing sharply first then staying stable and has different characteristics in different periods with active period,fluctuation period and stable period;Gravel and vegetation root system are the main reasons for the fluctuation of water breakthrough curve.The radius of soil macropores ranged from 0.03 to 4.71 mm and mainly concentrated in the 0.11².36 mm under different vegetation restoration models.There was a significant linear correlation between the mean radius of soil macropores and the steady effluent rate and saturated hydraulic conductivity,the soil macroporosity ranged from 0.03%to 16.58%,and the mean radius determined 65%variances of steady effluent rate and 42%of saturated hydraulic conductivity.?6?Soil preferential flow under different vegetation restoration models were focused on the 0⁴0 cm soil layer and the proportion of dye area ratio was more than 93%of 0⁶0 cm soil layer.The 0⁵cm soil layer dye coverage ratio of arbor forest was higher than shrub land and weeds and the order was Ulmus pumila land>Robinia pseudoacacia land>mixed forests land>farmland>shrub land>weeds land.The order of 0⁶0cm soil layer dye coverage ratio under different vegetation restoration models was Robinia pseudoacacia land?26.48%?>Ulmus pumila land?20.12%?>mixed forests land?17.32%?>farmland?15.06%?>shrub land?13.97%?>weeds land?10.07%?.There was a good linear relationship between the dye area ratio and the depth of soil layer.The Spearman correlation analysis was carried out between soil factors,water factors,vegetation factors and dye area ratio has significant positive correlation?P<0.01?with gravel content,mean radius of soil macrospores,soil saturated hydraulic conductivity,root weight density,<1 mm root length density,significant negative correlation?P<0.01?with bulk density,water content,significant positive correlation?P<0.05?with 1² mm root length density,2⁵ mm root length density.?9?The environmental factors,which were most relevant with soil preferential flow area,such as soil factors?total porosity,capillary porosity,soil macropores radius,gravel content,clay content,the proportion sand and silt content?,water factors?Soil water content and saturated hydraulic conductivity?,vegetation factors?root weight density,<1 mm,1² mm,2⁵ mm root length density?,has been used as soil hydrological effect evaluation index of dump vegetation restoration,using the AHP method,a reasonable evaluation index system of soil hydrological effect was established.Comprehensive weight of each evaluation index lies between 0.0318⁰.1462.Robinia pseudoacacia forestland,elm forest,mixed forest,shrub land,corn and grassland soil hydrology effect index size in turn for Robinia pseudoacacia land>mixed forests land>Ulmus pumila land>shrub land>grassland>farmland?0.361?,compared to farmland were increased 53.41%,48.17%,44.4%,18.89%and 3.96%.Therefore,from the perspective of soil hydrological effect,the best pattern of vegetation restoration in Haizhou opencast coal mine is Robinia pseudoacacia.