Search

Human activities commonly dominate the water source, such as moisture conditions, even for the surface subsidence, fissure zone, more severe groundwater exploitation, and complex precipitation in the semi-arid areas. This study aims to determine the variation of groundwater level and water content in the vadose zone in typical mining areas of Northern Shaanxi Province in China. The relationship between precipitation and groundwater was established by in-situ observation, statistical and wavelet analysis from the perspective of the water cycle. Some parameters were also measured, including the precipitation, groundwater table and soil moisture content in the vadose zone under the disturbance of coal mining. Particularly, the vadose zone dominated the infiltration, evapotranspiration, groundwater recharge and discharge in the water cycle. The interaction mechanism was also proposed for the response of groundwater level and water content to the changes in precipitation in both unmined areas and mining areas. The self-test system, groundwater observation wells and sensors were used to evaluate the rainfall, phreatic water level, soil moisture, and water potential in the mining areas. The soil water movement was monitored in the depths of about 10, 20, 30, 40, 50, 80, 100, and 150 cm in the unmined areas and in the depths of about 10, 20, 30, and 50 cm in the mining areas. After that, an evaluation was made on the variation of groundwater level under the disturbance of coal mining, the trend of soil moisture content with the depth, and the relationship between soil moisture content and rainfall response before and after coal mining. The results show that there was an outstanding response of groundwater level to precipitation in the unmined areas, where the absolute value of correlation coefficient reached more than 0.7. There was also a lag of about four or five months. There was no effect of small intensity of precipitation (like 50 mm) on the soil water content near the depth below 100 cm in the unmined area, but the larger precipitation (60 mm) infiltrated the depth below 100 cm. The groundwater level continued to decline, indicating the weak relationship between groundwater level and precipitation after the disturbance of coal mining for about several years. The moisture decreased with the increase of depth in the vadose zone, indicating the gentle fluctuation range of dynamic change. The soil moisture was less vulnerable to the external influence, as the farther away from the ground. There was an outstandingly different trend of soil moisture content with the rainfall at different depths, although no significant response of water content to precipitation at the same depth. In addition, the maximum soil moisture content in the mining area occurred earlier than that in the unmined area, indicating a reduced range overall. In particular, the precipitation increased significantly in July and August. The reason was that the fissures caused by coal mining shortened the precipitation time to recharge the shallow groundwater. There was no response at the depth below 50 cm to the small intensity of precipitation (like 30 mm). In general, the coal mining caused the drop in water level, resulting in the thickening of the vadose zone, whereas, the loss of water increased in the vadose zone, resulting in the rainfall infiltration of groundwater recharge decreased, further aggravating the drop of water level. Accordingly, the findings can provide theoretical support for the water cycle mechanism under coal mining. [ABSTRACT FROM AUTHOR]

Organic acids are ubiquitous in litters and rhizosphere in terrestrial ecosystem, and low molecular weight organic acids and humic acids are two common acids among them. They play a significant role in soil genesis, soil fertility and soil decontamination. However, the efficacy of organic acids in restoring vegetation in coal gangue is poorly understood. We took the coal gangue at Panji coal mining in Huainan city as an example. Low molecular weight organic acids and humic acid solution each at concentration of 10 mmol/L were added into the coal gangue in a 120-day incubation. The change in physical and chemical properties of the gangue was measured periodically. The results showed that the organic acids, especially malic acid and humic acid, promoted refinement of the gangue mineral particles and particle agglomerations, and helped improving aggregation of the mineral particles in the gangue. The incubation increased the clay particles by an average 81.9% and reduced the proportion of silt and very coarse sands by an average 21.05% and 62.34%, respectively. Many coarse sands were broken down to silt and clay which in turn formed aggregates. The pH, electrical conductivity (EC) and bioavailable nutrients in the coal gangue debris responded differently to the organic acids and incubation time. The pH of the studied gangue was 6.72 prior to incubation, and amending it with tartaric acid, oxalic acid and humic acid increased the pH to 7.69, 7.75 and 7.71 respectively. The pH changed with time in all the treatments; in the malic acid treatment, it changed in an "N" shape. In all treatments, EC changed with time in an opposite direction to the change in pH. The EC of the gangue was 416.67μs/cm prior to the incubation; the incubation increased the EC in CK and the treatments with malic acid and citric but reduced it in other treatments. Specifically, incubating with malic acid increased the EC by 146.78%, the highest among all treatments. Incubation with organic acids promoted the release of alkali-hydro nitrogen (AN) and available phosphorus (AP) from the mineral particles, while incubation with malic acid improved the release of AN more than others. In contrast, the citric was most effective in releasing AP. In all treatments, prolonging the incubation enhanced the release of alkali nitrogen and available phosphorus. Water infiltration and addition of the organic acids inhibited the release of available potassium(AK) from the mineral particles in the early stage, but promoted the release of the potassium. However, there was no significant difference between the organic acids. The results presented in this paper shed insight into the efficacy of different organic acids in remediating coal gangue. [ABSTRACT FROM AUTHOR]

Dumps in coal mine occupy huge areas of land and cause many problems, therefore, dumps reclamation become an important issue in ecological restoration. The reconstructed ecosystem of the reclamation dump is affected by various disturbance factors, which causes it to be unstable and prone to degradation. The disturbance influences the stability of reconstructed ecosystem and decides the success or failure of the ecological restoration in coal mine. Therefore, it is important to evaluate the recovery process of the reconstructed ecosystem. Based on the MODIS global disturbance index (MGDI) and vegetation disturbance index, which are based on MODIS data, we constructed the dump reclamation disturbance index (DRDI) by combing land surface temperature (LST) and enhanced vegetation index (EVI) using Landsat data. DRDI can provide higher spatial resolution than MGDI and VDI. EVI indicates the vegetation structure, and LST indicates the function of vegetation. The best status of reconstructed ecosystem is estimated by the maximum EVI and minimum LST, which is compared with the status of every year. DRDI is used to measure the vegetation recovery process and the degree of disturbance of vegetation in dumps. This study calculated the disturbance index of Antaibao opencast coal mine dump in Shanxi province, China for 28 years. This study combined remote sensing analysis with field validation data to analyze the spatial and temporal dynamics of characteristics for reconstructed vegetation restoration and interference. The results indicated that: in the early stage of reclamation, the areas with great disturbance showed highly spatial aggregated. The areas with disturbances had been gradually decreasing and took about 10 years for the vegetation structure and function to recover to the natural state in the reclamation dump, when the disturbed area could be reduced to the degree between 1.32% and 17.76%. DRDI could reflect the reclamation process and reveal spatial heterogeneity. The four dumps in Antaibao coal mine showed different stability periods and distribution characters of disturbance, which were influenced by dumping (coal gangue), reclamation strategy and vegetation reconstruction mode, as well as topography. Due to the spontaneous combustion of coal gangue, South Dump was more unstable than other dumps. Inner Dump began to reclaim later than other dumps but has entered a stable state relatively quickly, which was because of fine topography condition. The Western dump and its expansion area showed a degradation and great disturbance, where the surface vegetation covers mostly wasteland, grassland and cultivated land. DRDI can effectively identify the spatial extent and severity of disturbances for vegetation in reclamation dumps. DRDI is intuitive, effective and easy to implement. Its data can be easily obtained, and the calculation method is simple. It can effectively monitor the restoration properties of the reconstructed ecosystem for post-review evaluation of land reclamation. The quantitative analysis between influencing factors and disturbance index will be a key point in future research. Applying DRDI in evaluating the effect of reclamation in dumps will provide references to optimizing reclamation strategy and improving the efficiency of reclamation. For future research, DRDI can be combined with VDI to distinguish the causative factors of restoration character. [ABSTRACT FROM AUTHOR]

Subsided mined-land reclamation with Yellow River Sediments is an effective way and a win-win strategy for reducing the Yellow River sedimentation and accelerating mined land reclamation by using sediments as filling materials, which is of great significance to improve the regional ecological environment. In order to analyze the maximal supply amount and sediments demand for the filling reclamation of mining areas in the Yellow River basin, in this paper, we took the Yellow River and 23 national planning mining areas within 150 km away from the main sediments deposition segments of the Yellow River as the study area. Through the analysis of supply and demand of sediments for the filling reclamation of mining areas, the river segments and mining areas suitable for filling reclamation were preliminarily identified and the schematic sediments transport paths were also designed. Firstly, the sediments balance equation was used to estimate the sedimentation amount in main sediments deposition segments of the Yellow River in 1950－2013. Secondly, the sediments demand for filling reclamation of all mining areas within the study area was estimated. Based on the above two steps, we analyzed the spatial difference on the relation of Yellow River sediments supply and demand for the filling reclamation in all main sediments deposition segments. Finally, the sediments transport paths of different mining areas were designed as a whole by following the principle that the path should be shortest for minimum construction and labor costs involved. The results showed that the main sediments deposition segments of the Yellow River are Bayangol－Toudaoguai and Mengjin－Lijin, whose total sedimentation amount was 14.431 billion tons in 1950 －2013. Therefore, the sedimentation was the most serious in the river segment called Mengjin－Gaocun, where the accumulated sedimentation amount was 11.475 billion tons in 1950－2013. By the distance difference from the Yellow River, those 23 mining areas were further divided into three types of mining groups, including nine short-distance (S1) mining areas, 10 middle-distance (S2) mining areas, and four long-distance (S3) mining areas, which were 0 - 60 km, >60 - 120 km and >120 - 150 km away from the Yellow River, respectively. Their total sediments demand amount was about 22.512 billion tons by 2013. The spatial relationship between the supply and demand of the Yellow River sediments was unbalanced, thus not all mining areas could be reclaimed with Yellow River Sediment for insufficient sediment in some river segments. In the river segments including Bayangol－Sanhuhekou, Huayuankou－Gaocun, Aishan－Lijin, the sedimentation amount could cover the reclamation demand, thus all the mining areas could be filling-reclaimed using the sediments only judging by the difference between the sediment supply and reclamation demand, but in the river segments including Sanhuhekou－Toudaoguai, Mengjin－Huayuankou and Gaocun－Aishan, the sedimentation amount was less than the reclamation demand, thus only part of the mining areas could be suitable for the sediment-filling reclamation application. As a result, 7 S1 mining areas and 5 S2 mining areas, including Baotou, Yima, Jiaozuo, Zhengzhou, Feicheng, Huang Hebei, Zibo, Wuhai, Pingdingshan, Jincheng, Hebi and Xinwen, were comparatively suitable for filling reclamation by both sediments transportation length and sediments sufficiency or not, whose total sediments demand was 4.531 billion tons around and 4.488 billion tons, respectively by 2013, about 9.019 billion tons in total, accounting for about 40.06% of the total sediments demand of all mining areas and about 62.50% of the total sedimentation amount in the study area. The total water involved for sediment transportation to the mining areas suitable for filling reclamation was about 14.881 billion tons by 2013. The sediments transport paths length of the mining areas suitable for filling reclamation was about 21.98 - 109. 02 km away from the Yellow River. The total sediments transport paths length to the suitable mining areas was about 643 km. The study is the foundation for the wide-scale promotion of the filling reclamation technology of mining areas with Yellow River sediments, and is helpful for the subsequent feasibility study, the relevant planning and reclamation policies making. [ABSTRACT FROM AUTHOR]

North China Plain is the main coal production area with sedimentary deposit coal seam overlaid by the thicker soil layer above. The decrease of land surface elevation typically occurs at the rate in centimeters per year. Subsidence causes permanent inundation, especially topography gradient increase on the boarder of subsidence, surface runoff change, soil and water loss, and soil quality decline. It is critical to study the relationship among subsidence, surface runoff and soil quality change, and find the key factors that control the water and soil loss. In this paper, a two-dimensional undisturbed soil field experiment is performed, simulating subsidence process during coal mining. The data monitored in the experiment include surface subsidence, soil structure development, ammonia concentration and particle size change of soil during the rainfall-runoff process. Results show that underground mining not only changes surface topographic gradient and soil structure significantly but also aggravates the transport intensity of nutrient and particle in soil with runoff in the horizontal direction. Moreover, the soil crack produced by surface subsidence forms a series of groundwater preferential flow paths and promotes nutrient transport towards deeper layer. Firstly, in the horizontal direction, the ammonia content decreases by 14% on average in the subsidence with a length of 1.2 m and a slope of 2.1o after simulated rainfall of 122 mm. Secondly, in the vertical profile, the original ammonia peak value in the surface layer is 8.8 mg/kg, migrating a depth of 30 cm downwards. Thirdly, soil texture changes ununiformly in different subsidence parts. On the sloping bottom over the distance of 1.2 m, the fine-grained soil clay (≤ 2 μm) content decreases from 2.5% to 2.1%, and the average rate of soil clay loss is 16%; coarse-grained sand (≥50μm) increases from 3.2% to 3.8%, and the average increase rate is 3.6%. Reversely, the amount of clay at the bottom increases from 2.5% to 2.8% and the cumulative increase rate of clay content is 12%. This study shows that during the development of the subsidence basin, the soil crack experiences an evolution process of soil force changing from tension to compression. Preferential flow of soil crack has become an important driving factor for soil erosion in coal mining subsidence areas. In the tension stage of the crack development, the surface runoff would move deeper directly where the preferential flow paths are dominant. Part of the ammonia and soil particles in the soil would transport through these shortcuts with the runoff and infiltration. Furthermore, this process of crack preferential flow decreases the amount of lateral migration of soil nutrients and particles in the runoff and infiltration process and enhances profile transport. This process causes a rapid decline of soil fertility than usual. Fine particles move to the deeper layer and coarse particle proportion increases. The water and soil loss are strengthened. Therefore, the decrease of the quality of the soil caused by mining subsidence is completely different from the horizontal erosion type runoff erosion in the area where natural slope is predominant. Soil degradation caused by mining subsidence is more serious, and the soil crack preferential flow is the important driving factor to reduce the soil quality in coal mining subsidence area. It does matter to carry out control technology research for soil quality and improve the soil quality and land utilization efficiency in mining area. [ABSTRACT FROM AUTHOR]

The redevelopment of abandoned coal mine industry square (ACMIS) has become an important issue, as the number of abandoned sites has been increasing. Meanwhile, redeveloping the ACMIS is the basic requirement of the Chinese urban renovation and restoration strategy. Since reusing ACMIS is time-consuming and cost-consuming, developing an assessment tool to prioritize the renewal processes is necessary. Many existing assessment tools are not appropriate because they mainly focus on ecological aspects, while neglecting urban planning issues. Thus, this paper proposes a driving force-state-response (DSR) model of ACMIS which integrates planning, land rehabilitation and ecology, and analyzes the factors influencing the DSR framework. Then, the paper creates a comprehensive assessment system for prioritizing the redevelopment of ACMIS, which includes stakeholders' requalification objectives and perspectives related to the ACMIS regeneration process. The assessment system takes into account 3 pillars, which are 6 driving force factors (agglomeration degree of ecological agriculture, agglomeration degree of culture-oriented travel, high-way status, public transportation status, distance from downtown, accessibility of public service facilities), 9 state factors (soil conditions, soil pH value, damage degree, degree of heavy metal pollution, risk degree of geologic hazard, architectural integrity, historic and cultural value of modern architectures, status of underground space, municipal infrastructure status), and response (planning and policy). The point scoring framework is used to quantify and classify indicators, while four-quadrant method is used to couple evaluation results. Based on the evaluation results, ACMIS has been divided into 4 classes, high driving force - high state (HDFHS), high driving force - low state (HDFLS), low driving force - high state (LDFHS) and low driving force - low state (LDFLS). According to the land use planning, the development sequence is divided into 3 stages: The first development sequence is composed of HDFHS, the second development sequence is composed of HDFLS and LDFHS, and the third one is composed of LDFLS. The method has been applied to the Jingxi coal mine case study (Beijing, China), and the result showed that 3 sites named Changgouyu (D=3.818, S=3.848; D is driving force and S is state), Datai (D=3.732, S=3.732) and Muchengjian (D=2.646, S=4.522) in the city inventory were included in the first redevelopment sequence, and Wangping (D=4.240, S=3.187), Qianjuntai (D=2.248, S=3.887) and Daanshan (D=1.792, S=4.39) in the second redevelopment sequence, while Anjiatan (D=2.118, S=1.464) and Huapogen (D=2.798, S=1.907) in the third redevelopment sequence. It reveals that an adapted and structured assessment approach truly contributes to integrating urban planning into ACMIS regeneration. The resulting assessment should be a valuable aid to cities and governments as they plan their ACMIS regeneration projects. [ABSTRACT FROM AUTHOR]

Mining areas with intensive resources exploitation and utilization have undergone different kinds of environmental influences, such as water pollution and land use and land cover change (LUCC). The extensive coal mining in China has led to significant regional land use change resulting in major ecological damage. In order to research the impact of coal exploitation on landscape pattern change in coal mining area, taking Peibei mining area in Xuzhou City, Jiangsu Provinces, China as an example, the changes in land use and landscape pattern were analyzed quantitatively based on remote sensing (RS), geographic information system (GIS), landscape ecology and mathematical statistics. Influence of the scale and intensity of coal mining on variation process of land use structure and landscape pattern was mainly studied from the perspective of coal industry life cycle. At the same time, the driving factors of land use and landscape pattern change were analyzed from coal mining, economy, urbanization and land reclamation policy. The results were as follows: 1) Over the last 20 years the landscape structure and landscape pattern of land use in the mining area have changed significantly with the continuous exploitation of coal resources, which were mainly manifested by the decrease of cultivated land, forest land and unused land and the rapid increase of industrial and mining construction land and subsidence water. In particular, the subsidence water increased from 56.38 hm2 in 1994 to 1254.31 hm2 in 2014, and increased by about 22 times. The process of farmland transformed into construction land and subsidence water has become intense and frequent since 2000, in which the coal mining area has been in stable exploitation period. 2) Landscape type index showed a rising trend in fluctuation and landscape fractal characteristics tended to be simplified and regularized. The patch type index of cultivated land, forest land and garden plot overall declined, but that of industrial and mining construction land and the subsidence water increased continuously, which indicates the landscape of mining area tended to be simple and uniform. 3) Furthermore, correlation analysis and Mann-Kendall abrupt change test show that there is a strong correlation between coal resources exploitation and landscape index change. The abrupt changes of largest patch index (LPI) and aggregation index (AI) of cultivated land occurred in 1999 and 2001 respectively, and showed a rapid downward trend in 2003, which shows that the coal resource exploitation first affects the landscape dominance of cultivated land and then influences the aggregation degree of cultivated land patches with the increase of coal mining intensity. The AI of subsidence water area had a significantly rising trend in 2 periods, 1997-2006 and 2011-2013, but no significant change in 2006-2011, and the LPI of subsidence water area was increasing gradually over the whole period. The main reason is that continuous large-scale exploitation of coal resources seriously resulted in ground subsidence, damage and loss of arable land, vegetation field reduction and landscape fragmentation, and that the management of subsidence area got some effects through land reclamation and landscape restoration in mining area, which were showed as the increase of cultivated land and water area, and the decrease of landscape fragmentation. These results provide an important guide for land reclamation and ecological restoration of damaged landscape in coal mining areas. [ABSTRACT FROM AUTHOR]

The evaluation of land damage degree is an important basis for the formulation of land reclamation plan and the establishment of compensation standard for farmers in coal mining subsidence area. Mining subsidence area with high groundwater level has the characteristics of flat terrain, lower phreatic water depth, more recoverable coal seams, large thickness and big surface subsidence coefficient which lead to severe surface subsidence and seeper. Land is seriously destroyed. Thus, this paper takes Dongtan coal mine as an example to evaluate land damage degree of subsidence area with high groundwater level that will be damaged by coal mining from 2014 to 2018. The underground water level more easily rises above the surface elevation after mining, which leads to surface seeper in coal mining area with high groundwater level and when the perennial seeper is formed, there will be total crop failure for farmland. In Dongtan coal mine, the maximum buried depth of groundwater is 4 m. When the surface subsidence depth is more than 4 m, there will be perennial seeper, and therefore, the area with sinking depth of more than 4 m is designated as severely damaged area by the limit condition method. Based on a systematic review of existing research, the evaluation index system of other areas with sinking depth of no more than 4 m is constructed and evaluation units are divided with proper method. The weights of the indices are determined by the method of relationship of the order based on centralized decision-making of fuzzy opinions. Damage degrees are evaluated by the extension method. The final evaluation results show that the total damaged area of land is 1 675 hm2, of which the slightly damaged area is 968.2 hm2, the moderately damaged area is 379.53 hm2, and the severely damaged area is 327.27 hm2. The comparison with the simple empirical method of determining damage degree by means of surface seeper shows that the empirical method often underestimates the level of land damage in the mining area with high groundwater level. Areas where differences occur are concentrated in the middle and lower slopes of subsidence basins. Tilt deformation causes the slope of the land to become larger, and increases soil erosion; the area is under tensile force, and soil compaction is reduced, which is not conducive to the growth of crops, so the region near middle slopes can also be moderately damaged area. For the subsidence basin in downhill region, squeezed effect improves the land compaction, which is not conducive to the absorption of water and fertilizer for crops, and the area is prone to salinization and swamping, which is not conducive to the growth of crops. Although there is no perennial water area, the extent of the damage can be severe. Therefore, when determining damage degree of the land in coal mining subsidence area with high groundwater level, the condition of surface seeper should not be deemed as the only standard. The method proposed in this paper provides a reference for this type of subsidence area: The perennial water area is designated as severe damage area by the limit condition method, and comprehensive evaluation index system should be constructed to evaluate damage degree of land in other areas. The study provides theoretical support for the development of land reclamation plan and the establishment of compensation standards of farmers in Dongtan coal mine, and provides a reference for the evaluation of land damage degree in the same type of coal mining subsidence areas with high groundwater level [ABSTRACT FROM AUTHOR]

The long history of exploitation in an old multiple-seam mining area has caused severe land destruction, and the reuse of subsidence land needs to consider many different aspects. The geological topographic map and mining historical data (excavating, reserves, and so on) from the Hegang coal mine (Heilongjiang Province, Northeast China) were collected and investigated. The objective of this study was to analyze the current damage situation, predict the future subsidence, and put forward a land reclamation model for coal-mining subsidence. ArcGIS was used for statistical data analysis. Mine Subsidence Predictive Soft (MSPS) and the Probability Integral method were used for both short-term (2014-2020) and long-term prediction (from 2021 to mine closure) of subsidence. The degree of damage of the Hegang coal-mining subsidence was evaluated according to the predicted results and relevant regulations. The results showed that the subsiding area extended continuously. It increased by 1 468.19 hm2 from 2013 to 2020. The severe damage area reached 411.37 hm2 in 2020. By mine closure, the subsiding area increased by 3 871.35 hm2, and the maximum sinking value reached up to 39.4 m in the Yixin mine. The area of severe damage reached 5 865.7 hm2, which was 56.34% of the area of the total damage. The reuse of subsidence land showed a temporal variation, and land use plans should be made in accordance to this variation. In the period of 2013-2020, 2 industrial parks were affected by coal mining mildly or moderately. From 2021 to mine closure, 3 industrial parks and 2 new residential areas were affected with moderate or severe damage. According to the stability characteristics of subsidence land, Hegang coal mining subsidence could be divided into 4 areas: a stable region, a temporarily stable region, a dynamic region and a future subsidence area. The subsidence land in the temporarily stable region had different stability characteristics in each period, and it was stable from 2014 to 2020 and continuously sank after 2020. The regional stability characteristics and damage gradation of the subsidence land were basic information for the spatio-temporal reclamation planning of subsidence land. Over time, reclamation planning should be based on fully considering the damage gradation by the time the coal mine would be closed and the stability of the subsidence area. The design of the planning process should follow the principles that the stable region would first be reclaimed, followed by the temporarily stable region, the dynamic region and finally the future subsidence area. Therefore, the Hegang coal-mining subsidence was divided into a priority permanent reclamation area, a priority temporary reclamation area, a dynamic reclamation area and a future reclamation area. The spatial layout should determine the utilization of land in accordance to the timing of stable subsidence, damage gradation, land type and the economic development of Hegang City. The functional orientation of the priority permanent reclamation area was alternative industrial land due to the land stability, which could promote the economic development of Hegang City. The functional orientation of priority temporary reclamation area was temporary industrial land where short-term industries could operate for about 7 or 8 years. Lastly, the functional orientation of dynamic reclamation area was farm land because of the large areas of dry land and the severe damage gradation. This could guarantee the food security in the area. [ABSTRACT FROM AUTHOR]

Coal gangue is the solid waste from coal mining. Because of weathering, the physico-chemical properties of the coal gangue exposed on the ground's surface changes constantly. In order to study the change of coal gangue physico-chemical properties under the effects of weathering, the electrical conductivity, pH value and cation exchange capacity, 3 major physico-chemical indices are chosen to analyze their change characteristics and general regularities with the weathering time and the buried depth of coal gangue. The research chooses the distributing area of coal gangue with different weathering age, and divides the research layer into upper layer and lower layer, which are from surface to 30 cm depth and from 30 to 60 cm depth, respectively. A total of 135 samples from 5 coal gangue hills with different weathering age in Panbei, Panyi as well as Xinzhuangzi coal mines in Huainan mining area are collected with the stratified sampling method. The results show that there are certain change regularities of the physico-chemical properties of the coal gangue. The electrical conductivity and pH value of coal gangue decrease with the increasing of weathering age. And the cation exchange capacity increases along with the increasing of weathering age. The 3 indices of fresh coal gangue have a faster decrease rate within the early 2 a. The electrical conductivity reduces by 30% and the pH value falls by nearly 10% within the early 2 a. Then they change slowly. The cation exchange capacity can be increased by 17% within the early 2 a, and then its change grows slower. The change characteristics of physico-chemical properties of the coal gangue in profile are also obvious. Through the comparative analysis of the upper and lower layers, it is found that the electric conductivity and pH value in the upper layer are generally slightly higher than that of the lower layer, while the cation exchange capacity in the upper layer is slightly lower than that of the lower layer. The difference of pH value between the 2 layers is only from 0.1 to 0.3. The spatial and temporal variations of coal gangue conductivity, pH value and cation exchange capacity are all closely related to the weathering time or the degree of weathering. The great change occurs in the physico-chemical properties of coal gangue exposed to the ground's surface within 2 a. It shows that the weathering is significant. Of course, the temperature effect and hydrolysis as well as other physical processes play the role in the process. Lumpiness decrease of coal gangue due to physical weathering can speed up the change of chemical and other physical indicators. From the angle of the mining area land reclamation, these changes of the physical and chemical properties of coal gangue will be in favor of land reclamation in the mining area. The results provide the theoretical basis for land reclamation of coal gangue storage area. [ABSTRACT FROM AUTHOR]

The surface of the coal mining subsidence area will continue to sink at a relatively slow speed until it reaches limit, and the continuous settlement will inevitably affect the choice of land reclamation time, the growing crops which need nutrients from the land, and the normal use of agricultural facilities. It is very necessary to study the dynamic settlement of land over time to guarantee the time of land reclamation and the effectiveness of agricultural production. Time effect parameter in the Knothe function was analyzed in this study, and found that the parameter value had a great influence on the dynamic calculation of the surface subsidence and stability time. In the short period after mining, the bigger the parameter was, the greater the surface subsidence, and vice versa. And the bigger the parameter, the shorter the time needed for the surface from starting sinking to reaching the stability, and vice versa. In fact, the parameter was changing over time; the parameter in different periods were obtained based on the surface dynamic subsidence and time firstly, then the values were fitted, and the parameter in any period could be obtained according to the fitted formula. The dynamic settlement of coal mining subsidence area was closely related to the time; the Knothe function was introduced into the probability integral model, and the new idea of the ultimate subsidence and stage subsidence in the coal mining subsidence area was proposed. The prediction model of land dynamic settlement in coal mining subsidence area was constructed based on the Knothe function, which could be used to calculate the stage subsidence value at any time according to the engineering requirements. The subsidence factor, which changed with the time and was obtained from the time effect parameter, was the most important parameter in the prediction model. In order to verify the reliability and practicability of the prediction model, the paper took the measured surface subsidence data from the 2407 working face as an example, and carried out the application of the model as well as got the parameter. The time effect parameter at the 6th, 7th, 8th, 9th and 10th observation were calculated, respectively, and the empirical formula of the time effect factor with the time was obtained by fitting. By using the fitting formula, the time effect factor at the 11th observation was calculated. The calculated and the actual observation value of the time effect factor were compared, and the relative error was only 2.6% and the fitting effect was good. In addition, the measured and predicted values of the surface subsidence at the 9th observation were compared and analyzed. The results showed that the maximum relative error of single point was 8.8%, the average relative error of single point was 1.2%, the overall root mean square error was 187 mm, and the overall relative root mean square error was 5.6%. The difference between the predicted and measured value was small, which further proved the reliability of the model. According to the calculation model, the ultimate and the stage subsidence in multiple periods for the surface of coal mining subsidence area were calculated. The analysis showed that the prediction model conformed to the actual condition. [ABSTRACT FROM AUTHOR]

Based on Landsat TM satellite remote sensing image data, the paper utilized the vegetation index and vegetation fraction to analyze their spatio-temporal evolution and its driving factors. Spatial heterogeneity and its driving mechanism of vegetation fraction were analyzed under the linkage of mining and reclamation. Based on regression coefficient, standard deviation, gradation conversion matrix, and so on, we revealed the response of the vegetation cover to the mining and reclamation activities with time through the analyses of the trend and fluctuation of vegetation coverage in the study area, the mining area and the reclamation area. The results showed that the vegetation fraction and its grade in different years had some similarity, and the pattern of spatio-temporal evolution was broken by mining and reclamation activities in open pit mines to some extent. The vegetation coverage in the study area was mainly the middle (Grade IV) and the middle-low (Grade III) level, and according to the average of many years, both of them accounted for more than 80% of the total area of the study area. The ratio of the area with increased vegetation cover degree to the area with decreased vegetation cover degree was 2:3, and correlation coefficient was between -0.9266 and 0.4805. The correlation was not significant in the range of positive value, but was significant in the negative part. Correlation coefficient from -0.9266 to -0.895 was through the significance test of 0.025, and vegetation damage was the most severe, which belonged to a very significant change, and almost all were distributed in the exploited Xi’er, Xiyi and Dong’er open-pit stope and their solid waste yard, industrial sites and road with an area of about 4.85 km2. The standard deviation (SD) of inter-annual vegetation fraction for the study area was in 0-0.49. The vegetation fraction of open pit area, dump and surrounding areas with a range of 1.5 km was significantly decreased, and had gradually converged. Reclamation revegetation would experience a “high-low-high” cycle in the study area, and according to the changes of vegetation reclamation, protection period must ensure more than 6 years in semiarid grassland. In the study area, the land reclamation standard was higher than the surrounding area, and the recovery effect was better. More than 70% of areas had the transition of vegetation fraction, and the transition was relatively frequent. The fluctuation degree for the area of Grade III and II was the largest, which were the most damaged. There was 90 percent of the area of GradeⅠwhich was transferred by the mining activities. To enhance the vegetation coverage in the study area, it was required to reduce the social pressure and improve the ecological resilience. To reduce social pressure, we should consider the coal mining and solid waste stacking technology, with minimal impact on the ecological process in the form of a layered, limited mining area and stope arrangement for solid waste. The improvement of ecological resilience should increase the input of land reclamation, and steadily improve the coefficient of vegetation restoration in the mining area. The research results will provide information support for the ecological environmental protection and decision making, restoration and management in the area of open pit coal mine. [ABSTRACT FROM AUTHOR]

Integration management model for mining includes five steps: stripping, mining, transportation, dump piled up and reclamation. There is immediate and indirect impact on ecosystem from land destruction in mining area. In this paper, a comprehensive assessment model was used to explore the ecological risk value as exemplified by Antaibao open-pit mine of Shanxi province, China. In recent years, most researches are done for ecological risk assessment from the perspective of landscape ecology and the risk of heavy metal contamination. However less attention has been paid to the comprehensive risk assessment in the coal mining area. The mining area ecological system is easy to be disturbed and more complicated than general regions. The establishment of the ecological risk assessment model of land destruction ecological risk value (ERV) mainly includes two aspects: the effect of Antaibao opencast coal mining exploitation and ecological sensitivity of mining area. The larger environment influence of mining area by mining exploitation, the higher risk the ecological system would have. On the other hand, if the ecological system is more sensitive and fragile, the resistance and the ability to recover are lower. In this paper, we divided the study area into 30 m by 30 m grid unit and evaluated each unit to realize the mapping and classification of eco-risk in mining area. First, mining area ecological risks were identified from two aspects, production process of the mining and land destruction type in mine area. A typical open-pit mine ecological risk causal chain in Loess Plateau Region was constructed. Second, ecological index based on remote sensing and land-use type was developed specially for assessing mining area ecological sensitivity. The index was combined with six indicators which were adjusted by the important ecological indicators frequently used in assessing regional ecology and special ecological situation in mining area. Third, the data of the cumulative effect evaluation of land destruction and GIS-based ecological sensitivity evaluation were applied to quantify the comprehensive value of ecological risk. The results showed that un-reclaimed dump was the highest risk area (32.91% of the total area). Due to the reclamation measures and management for many years, reclaimed dump and industrial site were stable (9.66% of the total area). However, the unmanaged dump process and weak supervision caused soil and vegetation degradation. Therefore, some part of reclaimed dump showed a higher risk (26.46% of the total area). The open pit was the lowest risk area (30.97% of the total area). It was helpful to take the corresponding management level and constructing the preventive measures according to the risk value of different area. The occurrence of the mining area ecological risk was a dynamic process. The potential risk of disclosure may delay. This meant that we should take preventive in the process of production. If the risk occurred, it would take great harm in the mining area fragile ecosystems. Ecological risk assessment in mining area needed to be from the original single risk evaluation to the multi-level risk assessment so that we can fully embody the application value of the risk assessment as an important means mining area compound ecosystem management. This study made ecological risk assessment on the land destruction of mining area in order to realize ecological quantification and spatial visualization of the open mining and put forward the risk prevention measures for the subsequent production management. [ABSTRACT FROM AUTHOR]

Open-pit coal mines are among the most drastic anthropogenic land disturbances. Using Wise County in the USA's Appalachian coal field as the study area, this paper evaluates the mine land disturbance and reclamation process over a 27-year period by conducting time-series analysis of multispectral remote-sensing data at the pixel scale. Twenty TM/ETM images obtained by the Landsat satellites, with 30 m spatial resolution, are treated as a multiple-year chronosequence. Polygonal vector files defining mining permitted areas and 6 high-resolution aerial images are used as auxiliary data; and the normalized difference vegetation index (NDVI) is used as a vegetative cover indicator. The methodology and study process include 3 steps. First, training data are prepared and multispectral image data are preprocessed. Data preprocessing includes band stacking, extracting the study area as image subsets, masking of cloud, cloud shadow and water, and computing NDVI based on each study-area pixel in each image. After the training data are generated, they are used to identify the NDVI thresholds for separating bare-ground from vegetated pixels, and ever-mined pixels from those un-mined. These separations are performed by visually inspecting each individual TM/ETM image displayed through a combination of the band of 2, 3 and 4 while referencing all available high-resolution aerial images and polygon vector files defining mining permitted area. Second, each pixel's time-series NDVI trajectory is constructed and analyzed. Based on individual inspection of training points' NDVI trajectory and qualitative trajectory classification, the characteristic parameters, including the NDVI maximum, the NDVI minimum, the difference of NDVI maxima before and after mining, the bare-ground threshold and ever-mined threshold, are designed, computed and used to identify whether the pixel is ever mined, revegetated or revegetated to the land cover level before mining. The relationship between NDVI minimal values and ever-mined thresholds for each study-area pixel over the full time series is computed and analyzed to determine if the pixel has been mined and, if so, the date of initial disturbance. For mined areas, the relationship between NDVI trajectory and bare-ground threshold for each point in time series after mining is analyzed to determinate if excavated land has been revegetated. For those revegetated pixels, the difference of NDVI maxima before and after mining is computed in order tofind if it has been fully revegetated. Thirdly, by the data analysis function of database software and the spatial analysis function of ArcGIS software, the distribution of different mining-reclamation types is analyzed. Except for un-disturbed pixel, each mined pixel was classified for each year; such classes include the mined and un-vegetated during the whole observation period; the mined and un-revegetated after mining; the mined and revegetated without fully restored to the level before mining; and the mined and revegetated with vegetative cover fully restored to the level before mining. Time durations of non-vegetated status and revegetation after initial mining disturbance are also computed for fully reclaimed pixels. The conclusions are as follows: 1) During 1984-2010, the mining disturbs 45.80% mining permitted areas; 66.45% mined land is re-vegetated, which includes 38.42% mined land with fully restored vegetative cover and 28.03% mined land revegetated but without fully restored vegetative cover; 2) The fraction of mined lands with fully restored vegetative cover varies positively with mining-site age, which is found to be 85.54%, 13.92%, and 0. 52% lands during the periods of 1984-1993, 1994-2003 and 2004-2010, respectively; 3) The average time for non-vegetated status and vegetated status prior tofull cover restoration on the mined lands is 6 and 12 years, respectively; while the 25th, 50th, 75th and 90th percentiles for non-vegetated status are 4, 6, 10 and 16 years, respectively; 4) For full restoration of NDVI-derived vegetative cover to the level before mining, the time is 12 years on average. Study results demonstrate that the analysis of pixel-scale NDVI trajectories can reconstruct mining disturbance and land reclamation history, and can disclose its spatial heterogeneity over the broad expanse of space and time. Hence, such analyses can provide a scientific basis for land reclamation management and policy decisions. We note, however, that restoration of the NDVI to the level before mining is not a reliable indicator of reclamation success when viewed alone, although it is easily measured with satellite remote-sensing data. In order to interpret NDVI-derived vegetative cover data as indicators of reclamation success, other factors such as vegetation type and land productivity should be also considered. [ABSTRACT FROM AUTHOR]

Nowadays, a large number of land reclamation projects have been carried out or in the process of construction in coal mining areas of Xinjiang, and it is necessary to build up classification index and discriminant model to evaluate the suitability of land reclamation, for reducing the destruction of land and sustaining the development of coal mine. This article focused on the research of the theory of suitability evaluation of land reclamation and established a discriminant model that was used for the evaluation of coal mining areas in Xinjiang. The main type of destructed land in Xinjiang was grassland and bare land, so the land reclamation suitability evaluation was aimed at grassland. The results of land reclamation evaluation were divided into the most suitable, moderately suitable, barely suitable and unsuitable. One of the core issues of land reclamation is to construct evaluation index system. Taking 15 coal mines in Xinjiang as the research subjects, based on Bayes discrimination analysis, the factors of suitability evaluation of land reclamation of mines were analyzed; combined with the characteristics of land destruction and ecological geography of coal mines in Xinjiang, 7 factors such as the slope of land reclamation unit after land destruction, the depth of land destruction or the deposit amount of land occupancy, the guaranteed rate of soil for land reclamation, the clay content in soil, the thickness of topsoil, river runoff for irrigation of land reclamation unit and the content of organic matter in soil were selected as the evaluation factors. Each evaluation factor quantization value was taken from the measured value and the related report data. The 76 land reclamation units of 15 coal mines were used as the study samples. The Q clustering analysis method was used to classify 76 samples. The clustering analysis used the method of average connection to define the distance of categories for merging samples, and the distance was measured by the squared Euclidean distance. The results showed that the best plan was the 4 categories. Compared with the code, the classification results of this method were more realistic and accurate. By taking the 76 land reclamation units of 15 coal mines in Xinjiang as the training samples, the Bayes discriminant model for suitability evaluation of land reclamation of coal mining areas in Xinjiang was established. This model was composed of 4 discriminant functions. Every sample was tested by using the resubstitution method, and the correct rate was equal to 98.7%. The discriminant model was applied to 2 coal mines in Xinjiang. The results showed that the classification results were entirely consistent with the neural network method and the combination of factor and clustering analysis. The classification results complied with the classification result range of the code and were more accurate and realistic. The results of the modelling test and calculation have proved that the structure of Bayes discriminant is stable, and the discriminant effect is ideal. This model has strong analysis ability for suitability evaluation of land reclamation in coal mining areas of Xinjiang. The biggest difference between the results of evaluation model and the code was that results of evaluation model are more specific and detailed than that of code, especially in barely suitable category and unsuitable category. The classification results of this model are more accurate. This evaluation model can be widely used in suitability evaluation for land reclamation of coal mining areas in Xinjiang. [ABSTRACT FROM AUTHOR]

Determining a reasonable reclamation sequence of the large volume of mining wasteland can protect the ecological environment and support the land demand of economic development and industrial transformation in mineral resource cities. Taking the Mentougou district of Beijing city as the study area, a method of constructing an index system based on the factors influencing the reclamation sequence for comprehensive evaluation is presented in this paper. The evaluation index system, which includes four levels of ecological conditions, reclamation cost, geographical conditions, and economic and social factors, is built to determine the reclamation sequence of mining wasteland. Eight specific indexes are included: extent of damage, the grades of ecological risk, reclamation cost, traffic accessibility, distances from towns, regional population density, regional per capita GDP, and planning guide. A sequence-evaluation model based on GIS is established based on the above index system. Considering the needs of administrative management, the boundary map of administrative villages in Mentougou district and the distribution map of coal mining wasteland were superimposed, taking the village as the specific evaluation unit. The weight of each index is determined by an analytic hierarchy process. Quantification of each index is then made, followed by determination of the reclamation sequence of coal mining wasteland in the Mentougou district. The result shows that there are total of 45 villages in which coal mining wasteland need reclamation. Among them, sixteen villages need reclamation in the near future, where the area of coal mining wasteland is 121.94 hm2. These villages are mainly located in the southern mountains of the Mentougou district such as Datai, Yongding and Zhaitang town. These regions have a long history of coal mining, and the ecological system is severely damaged. In addition, they lie at or adjacent to the Mentougou new town. The population density is high. Nineteen villages need reclamation in the medium term, where the area of coal mining wasteland is 105.41 hm2. These villages are mainly located northwest of Qingshui town and south of Zhaitang, Tanzhe Temple and Wangping town. Coal-mining wastelands in these areas are scattered, and ecological damage is relatively light. Ten villages need reclamation in the long term, where the area of coal mining wasteland is 54.27 hm2. These areas mainly located in the mountainous areas. Coal mining activities are relatively small, and population density is low. By investigation, the result is consistent with the actual situation, which can provide theoretical support for the determination of the reclamation sequence of coal mining wasteland in the study area. [ABSTRACT FROM AUTHOR]