| The coal gangue had become one of the biggest solid waste emissions in our country which caused serious environmental problems. How to restore the ecological system of coal gangue that had been one of the hot topics in today’s society. Due to the spontaneous combustion tendency in coal gangue, we usually take cover rolling method of governance. However the compacted soil structure is poor that vegetation can grow normally or not, and how to influence the vegetation on soil compaction, which directly related to the success of ecological restoration of coal gangue.The ecological restoration project had been implemented in Lu’an mining area in 2007 that 10 kinds of typical vegetation measures had been implemented under covering layer with soil. These measures were natural recovery A1, herb C1(Cosmos bipinnata Cav.), herb C2(Lolium perenne L.), herb C3(Astragalus adsurgens Pall.), tree-herb H1(Rhus Typhina Nutt.+Medicago sativa L.), tree-herb H2(Robinia pseudoacacia Linn.+ Lolium perenne L.), tree-herb H3(Platycladus orientalis(L.) Franco + Medicago sativa L.), tree-shrub-herb T1(Rhus Typhina Nutt.+Amorpha fruticosa Linn.+ Medicago sativa L.), tree-shrub-herb T2(Platycladus orientalis(L.) Franco +Amorpha fruticosa Linn.+ Medicago sativa L.), tree-shrub-herb T3(Robinia pseudoacacia Linn.+ Pinus tabulaeformis Carr.+Amorpha fruticosa Linn.+Lolium perenne L.). Plots were conducted aiming at different restoration methods as well asnatural slopes and damaged ones in 2012. Investigation including community structure of vegetation, physicochemical properties of soil and evaluation comprehensively on soil quality, water retention was analyzed. This research was aimed to provide technical basis and guidance for the re-vegetation construction, and provide a theoretical basis for the fire control in coal gangue. Results were as follows:(1) After 5 years of revegetation restoration, 10 species of typical vegetation measures had undergone some changes in structure. Artemisia annua Linn.was the dominant in the natural recovery; woody plant species did not change with no succession of species in 10 measures. In addition, single species in family and single species in genera was dominant in the process of coal gangue dump in study area.The differences in community characteristics of herb layer in 10 revegetation measures were significant. The herb C2 was the highest with 1.78 in Shannon-Wiener index as well as the highest index of 0.76 in Simpson, but the Pielou index was medium of 0.81. The index of Shannon-Wiener in natural measure A1 was 1.55 while the Simpson index was 0.73, but the Pielou index was medium(0.80). The tree-herb H2 was highest for 0.98 in Pielou index, but the Shannon-Wiener and Simpson index was low. The changes in 10 measures of the indexes of the biomass of herb was different. A1 and C3 were the highest, while tree-herb and tree-shrub-herb measures were lower. In addition, underground biomass was higher than that of aboveground at the early stage of revegetation restoration.(2) The analysis of M.Godron index resulted: the intersection of axises for 10 plantation communities were away from the point of 20/80 an indicator of stability, and the relative distance of euclidean distance in square were large. Overall, 10 vegetation measures of vegetation communities were in a state of instability. The herb C3 and natural measure A1 were relatively stable.(3) The effect of revegetation on physico-chemical properties of coal gangue were obviously improved. Compared with the bare land, bulk density and percentage of aggregate destruction(PAD) decreased significantly; soil clay and the mean weight diameter(MWD) increased significantly; the content of soil organic matter and N, P, K nutrients increased significantly; the nutrient content of 0-20 cm soil was higher than that of the 20-40 cm soil layer, but there were not significant differences in physical properties.Through the correlation analysis and sensible analysis, 5 soil quality indicators which included soil bulk density, sand content, MWD, organic matter and available phosphorus were selected. With the comprehensive assessment method, 0-40 cm soil index value was 0.357-0.668 that the soil quality was overall in the middle level. The herb C3(Lolium perenne L.) and the tree-shrub-herb T3(Robinia pseudoacacia Linn.+ Pinus tabulaeformis Carr.+Amorpha fruticosa Linn.+Lolium perenne L.) were the highest value in soil quality.(4) The water infiltration processes were basically the same and the time of steady inflitration was about 32 min. The initial infiltration rate and the steady infiltration rate of 10 measures were significantly different. The re-vegetation measures of soil saturated hydraulic conductivity were between 0.012-0.143cm/min. In addition to H2, H3 and T1, soil saturated hydraulic conductivity in other measures were quite low in depth which indicated the effect of supported water was better while it could reduce the water infiltration to the mountain in the coal gangue.Among the re-vegetation measures, soil water property were significantly different. On the 0-20 cm layer, the improvement function that included C3(Lolium perenne L.), H3(Platycladus orientalis(L.) Franco + Cosmos bipinnata Cav.) and T1(Rhus Typhina Nutt.+Amorpha fruticosa Linn.+ Medicago sativa L.) on soil saturated water storage and water-holding capacity in capallary were in better effect. The natural measure A1 and C3(Lolium perenne L.) had a better effect on water-holding capacity in non-capallaryIn summary, different re-vegetation measures showed some differences in vegetation community stability, soil quality and soil moisture characteristics. The herb measure C3(Lolium perenne L) with bag technology met the above three conditions with the relatively stable community structure, high soil quality(soil quality index value of 0.634), high soil saturated water storage and the low saturated hydraulic conductivity rate(0.043 cm/min). In the absence of the bag technology in other measures, T3(Robinia pseudoacacia Linn.+ Pinus tabulaeformis Carr.+Amorpha fruticosa Linn.+Lolium perenne L.) met the above conditions with relatively stable community, high soil quality(soil quality index value of 0.668), high soil saturated water storage and the low saturated hydraulic conductivity rate(0.024 cm/min). |
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