Study On Vegetation Recovery Potential Of Coal Mine Spoils In An Alpine Coal Mining Area

The muli coal mining area is a concentrated distribution area of coal resources in Qinghai province,which is located in the northeast of Qinghai-Tibetan Plateau.This region is characterized by a high altitude and a cold weather meaning an extremely fragile ecological conditions.After years of opencast mining activities,a large number of coal mine spoils are accumulated,which seriously affects the regional ecological and environmental security.In recent years,the artificial restoration practices have been carried out in this area,and some ecological benefits have been achieved to a certain degree.However,different cultivated plant species and restoration measures often result in great difference of the recovery effects,and some even lead to recovery failure.For the reasons mentioned above,it is urgent to study on the environmental adaptability of different cultivated species,the vegetation and ecosystem recovery potential of coal mine spoils under the different restoration measures.It is of great significance to guide the ecological restoration of this area by these efforts.In this study,the coal mine spoils in Jiangcang and Juhugeng coal field of mili coal mining area in Qinghai province were selected as the experimental field.The effect of the temperature drops in autumn?natural temperature reduction?on the cold resistance capability of different cultivated species were investigated.At the same time,a variety of artificial restoration measures were designed to estimate the recovery effects of vegetation and soil under the different artificial restoration measures and restoration times.On this basis,the evaluation model of health and recovery potential of vegeration and ecosystem of coal mine spoils were established.Byusing this model,we estimated the recovery potential of the different restoration measures,and found the most suitable ecological recovery measures and means of coal mine spoils in muli coal mining area.The main results were as follows:1.With the decrease of temperature in autumn,the free proline,Na⁺and malondialdehyde content of three plants?Elymus nutans,Poa crymophila and Puccinellia tenuiflora?increased gradually.Meanwhile,the soluble sugar content and the superoxide dismutase activity first increased and then decreased,the catalase activity showed different variation regularities,the K⁺content decreased gradually and the Ca²⁺content had no significant change.The overwintering survival rate of the three plants reached above 96%,and all of them could overwinter safely.Three cultivated grass species had developed different physiological and biochemical cold resistance mechanisms.By synthetic evaluation,the cold resistance capability of the three plant were as follows:P.crymophila>E.nutans>P.tenuiflora.The seed bank density of the three plants varied greatly.In conclusion,E.nutans and P.crymophila are more suitable than P.tenuiflora for the growth and development under the low temperature conditions.2.There were no significant differences in the community compostion and structure of artificial grassland among the different cold resistance measures such as mulching measures,spraying salicylic acid,mulching measures and spraying salicylic acid.The values of plant richness,diversity and evenness also showed no significant differences?P>0.05?,which mean a higher degree of community similarity among the different cold resistance measures.The vegetation coverage,density,height and aboveground biomass increased significantly by using the mulching measures,mulching measures and spraying salicylic acid compared with CK,while the spraying salicylic acid had no effect on the growth and development of vegetation.Thus,the measures of covering non-woven fabric in spring can accelerate the process of vegetation and ecosystem restoration.3.There were 4-5 plant species in artificial grassland covering the three different replaced topsoil depths?no replaced topsoil,0 cm;moderate replaced topsoil,20-25cm;heavy replaced topsoil,40-45 cm?by using the permafrost soils in the lower layer.The community compostion,the values of plant richness,diversity and evenness showed no significant differences?P>0.05?,which mean a higher degree of community similarity among the different replaced topsoil depths.There was a distinct difference in the plant community composition and structure between the undisturbed grassland and the other replaced topsoil plots.Vegetation coverage,density,height and aboveground biomass increased significantly?P<0.05?with increasing topsoil depth.The 40-45 cm plot had the highest vegetation coverage that was slightly lower than that of undisturbed grassland plot,and had higher aboveground biomass compared with the undisturbed grassland plot?P<0.05?.Soil properties such as total nitrogen,total phosphorus,available nitrogen,available phosphorus,available potassium increased with increasing topsoil depth,but did not change significantly?P>0.05?.Soil organic matter was significantly higher at the 40-45 cm topsoil depth than at other two depths?P<0.05?.The 40-45cm topsoil depth of replacement should be considered as effective method in reclaiming coal mine spoils.All soil properties,with the exception of total potassium,were positively correlated with the plant growth parameters.Based on the joint consideration of both restoration effectiveness and economy,fertilization especially using the organic fertilizer might,therefore,be used as a substitute for artificial replaced topsoil measures in artificial grassland to quickly improve soil quality and speed up the ecological restoration process of coal mine spoils through plant-soil interactions.4.There were not significant difference in plant species numbers among the different level of fertilizaition such as light fertilization,moderate fertilization,heavy fertilization,no fertilization within one year,no fertilization within 6years.With the increase of the fertilization,the growth and the propagation of E.nutans were promoted,and the proportion of importance value of E.nutans increased gradually,while the opposite trend were observed for P.crymophila and P.tenuiflora.Fertilization did not cause changes in community richness of artificial grassland,while community richness index decreased significantly after years without fertilization?P<0.05?.In addition,moderate fertilization measures are more conducive to the increase of vegetation coverage,density,height and aboveground biomass compared with other levels of fertilization.The application of too much or too little fertilizer is not benefit to plant growth,and non-fertilization especially for many years,will cause serious degradation of artificial grassland.With the increase of fertilization,soil total nitrogen,total potassium and available potassium did not change significantly,but available nitrogen,total phosphorus and available phosphorus increased in varying degrees.Soil organic matter first increased and then decreased,and soil pH value gradually decreased?P>0.05?with increasing fertilization.Thus,the application of moderate level or above the level of moderate fertilization is an effective measure to improve soil properties.5.Artificial grasslands were formed and developed,but the different vegetation community compositions,and the significant variations in plant growth characteristics?P<0.05?including vegetation coverage,height,density and above-ground biomass were observed among the three artificial restoration measures?revegetation,revegetation and replaced soil,revegetation and fertilization?.Soil organic matter content increased significantly?P<0.05?in three restoration measures plots than in the coal mine spoils plot.Compared with natural undisturbed grassland,there were not effective improvement of soil quality including soil fertility and pH value founded in the artificial grasslands by only 5-year restoration of three artificial measures.Single method such as artificial revegetation used alone is not conducive to ecological restoration.The combined methods by using artificial revegetation in combination with replaced soil or fertilization,have been proved to be effective to restore the ecological environment of coal mine spoils in alpine coal mining areas.6.There were not significant difference in species composition,which be characterized by simplicity and low species numbers,among the different recovery time plots.The important value of E.nutans and Pedicularis kansuensis increased gradually,while the opposite trend were observed for P.crymophila and P.tenuiflora with the increase of recovery time.Meantime,The community richness index increased?P>0.05?,the community diversity index decreased gruadually with increasing recovery time and reached significant level after 4 years restoration?P<0.05?.There were not significant difference in vegetation coverage,density,height and aboveground biomass among the different measures of recovery time plots?P>0.05?.In the short term,the plant growth of artificial grassland is relatively stable.With the increase of recovery time,soil total nitrogen showed no significant change,but soil total phosphorus increased and soil total potassium decreased to a certain degree.Soilavailable nitrogen,available phosphorus and available potassium decreased significantly by 49.68%?66.07%?18.67%respectively in the first 4years restoration?P<0.05?.Soil organic matter content increased significantly after 2 and 4 years restoration?P<0.05?.The soil pH value increased as a result of the slow transition from acidic to neutural soil.7.According to the regression equation and prediction model,with the increase of succession years of artificial grassland,soil total nitrogen remained unchanged,total phosphorus increased gruadually,total potassium decreased gruadually,soil organic matter increased significantly,soil acid-base property amended,soil available nutrient content such as available nitrogen,available phosphorus,available potassium decreased significantly,and vegetation coverage,density and aboveground biomass of artificial grassland had potential risks of decline.With the increase of restoration,it is still necessary to take measures such as fertilization and supplementary seeding to maintain soil nutrient status,vegetation coverage and community diversity,and to prevent artificial grassland degradation after soil amendment by replaced topsoil and revegetation in coal mine spoils.8.On the basis of establishing VOR/CVOR model,the vegetation,ecosystem health level and recovery potential of coal mine spoils in an alpine mining area were evaluated.In the process of applying this model,aiming at the ecosystem restoration characteristics of coal mine spoils,the CVOR model was optimized and OCVOR model including its concept and calculation method were introduced.Through a comprehensive comparison of the 18 restoration measures,we observed that the aboveground vegetation could be rapidly restored after the artificial restoration measures were applied.Under the same restoration conditions,although the vegetation growth condition was relatively good,but the ecosystem health level and restoration potential were still low and weak.During or after revegetation,the vegetation and ecosystem restoration potential were both higher by application of measures such as replaced topsoil by using soil in the upper layer or above the level of moderate fertilization.These methods are considered as the effective measures for vegetation and ecosystem restoration of coal mine spoils in muli coal mine region.The results obtained by cluster analysis are consistent with the 5 grades of VOR and OCVOR health level and recovery potential of the 18 measures.The results of cluster analysis are correct and can meet the actual situation.Based on the consideration of reducing economic input,the restoration measures,that was revegetation+mulching measures+above the level of moderate fertilization,should be applied as a priority adoption measure.Meantime,the use of this measure should be noted to avoid excessive fertilizer application to damage plant growth.In addition,supplementary seeding should be adopted to increase the coverage and biodiversity of artificial grassland.