Pingshuo Opencast Coal Mine Research Articles

Delimiting supervision zones to inform the revision of land reclamation management modes in coal mining areas: A perspective from the succession characteristics of rehabilitated vegetation

The rational delimitation of supervision zones is an important means of regional management that can effectively solve the problem of unbalanced development among reclaimed coal mine areas. In this study, 32 years of vegetation fractional coverage (VFC) series data from 1989 to 2020 were obtained for the area around the Pingshuo opencast coal mine. Then, the S-logistic function was applied to fit the VFC series data for each reclamation dump unit. Combined with the recognition results of coal mining and land reclamation years and by setting three delimitation criteria, the supervision zones of land reclamation that need to be better managed in the reclaimed dump sites were delimited. Finally, optimization revisions of the land reclamation management mode were proposed. The results showed that the effective reclamation zones of land reclamation occupied most of the study area, especially in the early reclaimed west dump, south dump and inner dump I areas of the Antaibao coal mine. The level one supervision zones, which were delineated as the general management zones, were mainly concentrated in the Anjialing inner dump, Nansigou dump, east dump, and west dump. The level two supervision zones, which were delineated as special management zones, were mainly concentrated in the Anjialing Nansigou dump site. Moreover, the Pingshuo coal mine dump sites were divided into four mode areas, namely, ecological conservation, ecological monitoring, ecological restoration, and ecological reconstruction, for the revision of land reclamation management. The proportion of area corresponding to each management mode was 49 %, 23 %, 24 % and 4 %, respectively. The management modes applicable to different reclaimed dump sites differed, and the specific management measures to be adopted depend on the succession pattern of the whole processes of rehabilitated vegetation. This study provides a new approach for delimitating the supervision zones of land reclamation and proposes revision management modes for the precise implementation of land reclamation development plans in coal mining areas.

Effect of soil compaction on hydraulic properties and macropore structure: Evidence from opencast mines in the Loess Plateau of China

Affected by heavy machinery, the soil compaction in the opencast coal mine area is serious, which will change the characteristics of soil macropores, then affect the soil hydraulic properties and damage the ecological environment in mining area. In this study, the disturbed soil samples from the dumping area of Pingshuo opencast coal mine of China were collected. The soil samples were processed in bulk density from 1.30 g·cm−3 to 1.70 g·cm−3, and the soil hydraulic properties were measured, and the soil macropore characteristics were obtained using computerized tomography scanning in laboratory. The path analysis method was applied to analyze the effect of macropore characteristics caused by compaction on soil hydraulic properties. Soil compaction resulted in severe effects on soil hydraulic characteristics and macropore properties. Under same soil suction, the water contents remained in soil decreased with increasing compaction. The explanatory variables (average Euler number (AEN), macropore throat number (MTN), and macropore fractal dimension (MFD)) were main determinants of soil-water characteristic curve (SWCC), and the indirect path coefficient of macroporosity. The effects of AEN and MFD on soil infiltration properties were relatively high. The bulk density of 1.4 g·cm−3 was a critical point of affecting macropore properties then affecting soil hydraulic properties, and some soil reclamation measures should be conducted to make bulk density < 1.4 g·cm−3 for compacted soil in opencast coal mining area. This study provides a basis for selecting technology of land reclamation and the subsequent monitoring and maintenance of soil quality in mining areas.

Deciphering the origin and controlling factors of mercury in reclaimed soils: a case study in Pingshuo opencast coalmineof China.

Considering the significant influence of mercury (Hg) contamination on the land reclamation inopencast coalmine, the spatial distribution patterns and ecological risks of Hg were investigated and the regulating factors of Hg mobility were determined in the South Dump of the Pingshuo opencast coalmine. The results show that the total Hg (HgT) contents of most soil samples (83.7%) vary from 6 to 50μgkg-1, while the potential ecological risk index (EIHg) values of most samples (79.8%) are lower than 80, indicating that most reclaimed soils are in relatively good conditions and the soil samples at high to very high ecological risk are mainly collected near the backfilled coal gangue. Moreover, the kriging maps of the geo-accumulation index (Igeo) indicate that the uncontaminated areas (Igeo < 0) and Hg-contaminated areas (Igeo > 0) in topsoil (0-10cm) are roughly divided by an "east-west arc" while the Hg-contaminated areas in other soil horizons are characterized by a "point distribution pattern". The slight Hg contamination in topsoil is mainly triggered by the atmospheric Hg deposition from the nearby coal-fired power plant, while the Hg contamination in other soil horizons should be attributed to the weathering and spontaneous combustion of coal gangue. On the other hand, Pearson's correlation analyses show that HgT contents were positively correlated with clay (r = 0.31, P < 0.01) and SOC (r = 0.53, P < 0.01) contents. This study can provide some insight for the land reclamation measures in the opencast coalmine.

Identification of land reclamation stages based on succession characteristics of rehabilitated vegetation in the Pingshuo opencast coal mine

Land reclamation is a dynamic ecological restoration process, and rehabilitated vegetation requires a certain amount of time to develop, stabilize and mature. The development characteristics of rehabilitated vegetation at different land reclamation stages are significantly different, and these differences can be used to identify the key stages of land reclamation. In this study, normalized differential vegetation index (NDVI) time series data from the western dump of the Pingshuo opencast coal area on the Loess Plateau from 1989 to 2018 were collected and analyzed by fluctuation analysis and filter processing with the Best Index Slope Extraction and Wavelet Transform (BISE-WT) filter to reveal the succession characteristics of rehabilitated vegetation. Then, the key periods of land reclamation under different vegetation types (arbor, shrub, arbor-shrub, and grass) in the dump were determined by S-logistic function fitting and derivative analyses. The NDVI time series changes in land parcels reclaimed in different years exhibited different interannual change characteristics. Based on the number of years required for the rehabilitated vegetation to reach a stable state, the average development period of land reclamation in eligible units in the mining dumps was thirteen years, including ten years in the rapid development period and three years in the steady development period. The differences in land reclamation periods among the different vegetation types were significant (α = 0.05), and the number of years required for each period mainly followed the order of arbor > arbor-shrub > shrub > grass. Analyzing the vegetation succession characteristics and identifying the key periods of land reclamation for different vegetation types is conducive to dynamically evaluating land reclamation effects and is expected to provide a basis for strengthening the implementation of manual intervention measures in reclaimed mining areas.

Construction of landscape ecological network based on landscape ecological risk assessment in a large-scale opencast coal mine area

The comprehensive effect of multi-source factors changes the landscape structure and reduces the quality of landscape ecology in large-scale opencast coal mine area, resulting in an ecologically fragile environment. Landscape ecological quality directly affects the flow and transmission of ecological functions, which is an important factor in the construction of landscape ecological network. In the study, based on the Landsat remote sensing images of 1986, 1996, 2000, 2009, and 2015 in the Pingshuo opencast coal mine area of the Loess plateau in Shanxi Province of China, the landscape loss index and ecological sensitivity index were selected to establish the landscape ecological risk assessment model, and the spatial and temporal characteristics of the landscape ecological risks from 1986 to 2015 were analyzed. Considering the impact of landscape ecological quality on ecological resistance, the Minimum Cumulative Resistance model (MCR) was applied to build a landscape ecological network based on the landscape ecological risk assessment in 2015 to identify the important ecological elements, and the complex network method was used to analyze the structure of landscape ecological network. The local risk level of the study area reduced with opencast coal mining; however, the overall risk level was improved with conducting land reclamation. The high-risk area showed a trend of spreading from southwest to northeast; the risk of the peripheral areas of urban construction land and mining land was relatively high, while that of the forest and grassland area was relatively low. The risk change of the study area was mainly affected by the mining scale, urban expansion, conversion of farm land to forest and grassland, land reclamation, and village relocation. Through the complex network method, the energy flow fluency and the relationship between nodes were enhanced after the optimization of the landscape ecological network, and the ecological elements for specific land use protection were identified. The research results can provide scientific basis for the optimization of landscape pattern and the construction of ecological security pattern in Pingshuo opencast coal mine area.

Intra- and Interspecific Interactions among Pioneer Trees Affect Forest-Biomass Carbon Accumulation in a Nutrient-Deficient Reclaimed Coal Mine Spoil

Pioneer trees play a key role in the recovery of a reclaimed ecosystem that is nutrient-deficient in the initial stage of reclamation. Clarifying the growth of pioneer trees and their response to intra- or interspecific competition is of great importance to help stewards manage reclaimed forest. Nevertheless, such documents are lacking. We utilized forestry inventory data from a R. pseudoacacia and P. tabuliformis mixed forest plot with an area of 8000 m2 to find out the effect of trees interaction on their growth (indicated by the amount of biomass carbon per stem) in a nutrient-lacking reclaimed ecosystem 17 years after reclamation in Pingshuo opencast coal mine, Shanxi Province, China. In total, 2133 tree individuals were measured and tagged; the kriging interpolation method was applied to map spatial variation of forest-biomass carbon (C). Univariate and bivariate mark correlation functions were employed to examine the effect of intra- and interspecific interactions on tree’s biomass C accumulation. The results showed that tree biomass C was 27.84 Mg ha−1 in the forest. C class structure of planted R. pseudoacacia followed inversed J-shaped distribution and seeded-in R. pseudoacacia and Ulmus pumila (a spontaneous species) had L-shaped distribution. P. tabuliformis, however, followed a nearly normal distribution. Patchy distribution was observed with regard to C spatial arrangement of all tree species. In terms of the intraspecific correlation of biomass C, no significant competitive or facilitative interactions (GoF p ≥ 0.05) was observed among conspecific trees of seeded-in R. pseudoacacia and P. tabuliformis. In contrast, significant negative interactions (GoF p &lt; 0.05) or repulsion correlations between biomass C of planted R. pseudoacacia individuals and U. pumila individuals were found at the scale of 1–2 and 0–8.5 m, respectively. In term of the interspecfic spatial correlation of biomass C, a significant positive interaction between the heterospecific individuals of planted R. pseudoacacia and seeded-in R. pseudoacacia was observed at the scale of 2.5–4 and 12.5–15 m. Similarly, seeded-in R. pseudoacacia and U. pumila were found to be attracted by P. tabuliformis at 7–9 and 0–2 m, respectively. Conversely, significant departure effect was observed at the scale of 1–3 m between the biomass C of U. pumila and planted R. pseudoacacia and 4.5–5.5 m between the biomass C of U. pumila and seeded-in R. pseudoacacia. Consequently, R. pseudoacacia and P. tabuliformis could coexist for a long term and P. tabuliformis was a species that facilitated the accumulation of C of other tree species. Overall, complex intra- and interspecific interactions in nutrient-limit reclamation ecosystem affected biomass C accumulation. R. pseudoacacia–P. tabuliformis mixed forest could be an efficient reclamation pattern to restore biomass C in the Loess Plateau area.

The reclaimed coal mine ecosystem diverges from the surrounding ecosystem and reaches a new self-sustaining state after 20–23 years of succession in the Loess Plateau area, China

Whether or not the completely destroyed ecosystem would follow a succession trajectory towards the surrounding forest ecosystem after restoration remains debatable. Here, a comprehensive dataset of thirty-five ecosystem functions were measured on five reclaimed opencast coal mine forest plots (two Robinia pseudoacacia - Pinus tabuliformis mixed forests with different technosol conditions: RPT and RPM; one R. pseudoacacia - Ulmus pumila - Ailanthus altissima mixed forest: RUA; one Picea meyeri - Picea wilsonii - Hippophae rhamnoides mixed forest: PPH; one R. pseudoacacia monoculture forest: RM) and one natural forest plot (Populus simonii monoculture forest: PM) in Pingshuo opencast coal mine, Shanxi Province, China. These functions were employed to examine the reclamation effects among plots in terms of four management scenarios (i.e., biomass productivity, carbon sequestration, general biodiversity conservation and nutrient accumulation) and to determine the affinities between reclaimed ecosystem and its native counterpart according to Bray Curtis Distance Algorithm. The results showed that after 20–23 years of succession, thirty-five ecosystem functions differed among plots and eight highest ecosystem functions were found in RPT and RPM (P < 0.05). In scenarios of biomass productivity, carbon sequestration, general biodiversity conservation and nutrient accumulation scenarios, RPM scored 0.645, 0.470, 0.467 and 0.578, respectively. Accordingly, RPT scored 0.458, 0.447, 0.405 and 0.515, respectively. Consequently, RPT and RPM had the highest scores in the four management objectives compared to other plots. With regard to the ecosystem affinities, RPT was analogous to RPM. Similarly, RUA and PPH resembled PM and RM, respectively. Overall, the pioneer tree species determined the reclamation quality in the dump in the long term, which could be referred as the “trigger effect” in the succession trajectory in reclaimed ecosystem, and the reclaimed coal mine ecosystem diverged from the surrounding ecosystem and reached a new self-sustaining state after 20–23 years of succession.

Three-dimensional quantification of macropore networks of different compacted soils from opencast coal mine area using X-ray computed tomography

Heavy machinery compaction in mining area is widespread, and seriously jeopardizes soil restoration. Characterization of soil macropores with three-dimensional methods is essential for understanding the reclaimed minesoil (RMS) development. The aim of this study was to demonstrate the application of X-ray computed tomographic (CT) scanning for analyzing soil macropore structure and to explore how soil compaction affects soil macropore properties. To achieve this, soil samples collected from Pingshuo opencast coalmine were tested through a laboratory scheme, which was conducted to simulate the real soil pore situation under increasing soil bulk density treatments of 1.3, 1.4, 1.5, 1.6, 1.7, and 1.8 g cm−3 (T1.3-T1.8). Three-dimensional (3D) macropore networks were observed via CT, and macroporosity, macropore number, area, volume and its connectivity were characterized. Soil compaction had a major impact on soil macropore characteristics. The macropores of the 1.3 g cm-3 treatment were well connected, whereas those of the 1.8 g cm-3 treatment were poorly connected and isolated from each other. Macropore number and macroporosity decreased significantly as the soil compaction increased. Moreover, a 3D visualization of soil pore connectivity results suggested that the macropore connectivity markedly decreased with increasing compaction level, with average Euler number increasing from 0.677 in the 1.3 g cm-3 treatment to 0.999 in the 1.8 g cm-3 treatment. Soil bulk density was negatively correlated with macropore throat number and thickness, indicating that the soil compaction causes a loss of pore connectivity. Despite using a coarse resolution, the combination of laboratory simulation tests and 3D visualization of soil macropores provides valuable data for identifying the differences in soil pore structure among compacted RMSs and monitoring the persistent effects of soil compaction caused by heavy machinery in the mining area. Furthermore, we recommend a new method combining 3D visualization techniques and hydraulic analysis in the study of compacted soils, and the establishment of soil restoration measurements to avoid further compaction in mining areas.

Soil nutrient variations among different land use types after reclamation in the Pingshuo opencast coal mine on the Loess Plateau, China

Soil nutrients are critical indicators of land reclamation effects and play significant roles in soil restoration in degraded mining areas; however, few studies have analyzed the characteristics and variations in soil nutrients after reclamation in ecologically fragile regions on the Loess Plateau. To analyze the spatial and temporal variations in reclaimed soil nutrients, an experimental field was established in an inner reclaimed dump consisting of four land use types (cultivated land (CL), forestland (FL), grassland (GL), and barren land (BL)) in the Antaibao mine on the Loess Plateau of China. Sampling was conducted in 2013 and 2017, with 78 and 81 sampling points, respectively. The soil available phosphorus (SAP), soil available potassium (SAK), soil total nitrogen (STN) and soil organic matter (SOM) contents at depths of 0–20 cm were measured at each sampling point, and the variations in soil nutrients were analyzed using two-way multivariate analysis of variance, geostatistical analysis, and correspondence analysis. This study revealed the following: (1) All the reclaimed soil nutrients tested increased between 2013 and 2017. (2) There were significant differences in the SAP, SAK, STN and SOM contents among land use types and reclamation ages, and land use type and reclamation age had an interaction effect on the reclaimed soil nutrients. (3) The spatial distributions of the SAP, SAK, STN and SOM contents in 2017 were significantly different from those in 2013 but were almost consistent with the distributions of soil nutrient changes between 2013 and 2017. (4) The most improved SAP, SAK, STN and SOM (SAP-VI, SAK-VI, STN-VI, and SOM-VI) were predominantly distributed in the GL, and there was no obvious trend for the other land use types. These findings are significant for the restoration of reclaimed soil nutrients and provide reasonable land use type options for land reclamation in coal mining areas, especially in ecologically fragile areas on the Loess Plateau.

Tempo-spatial changes and main anthropogenic influence factors of vegetation fractional coverage in a large-scale opencast coal mine area from 1992 to 2015

The surface soil and vegetation had been destroyed by opencast mining, leading the decrease of the vegetation fractional coverage, which caused a severe damage to the mining area and ecosystems. However, land reclamation in mining area minimized the damage to the environment and was an important part of mine production and construction to improve the vegetation fractional coverage and restore the local ecological balance. To analyze the effects of anthropogenic activities on vegetation, the vegetation fractional coverage (VFC) and vegetation index (VI) of the whole Pingshuo opencast coal mine area from Shanxi province of China and four individual reclaimed dumps in this coal mine area were calculated respectively based on remote sensing images. The spatial distribution of vegetation fractional coverage was analyzed using Moran's Index. From 1992 to 2015, the vegetation fractional coverage of the whole coal mine area increased from 0.31 to 0.53, showing a benign development trend with significant change from 2000 to 2015, and it was the lowest in 2009. Moreover, The vegetation fractional coverage transformed from extremely low coverage, low coverage, to middle coverage, middle high coverage, and high coverage during 23 years, which was improved clearly. The long reclamation period is conducive to vegetation restoration, and the reclamation project has a direct effect and significance for the restoration of the ecological environment of the mining area. The vegetation fractional coverage of four dumps in the study area were the lowest at the initial reclamation time, and increased with increasing reclamation time. The vegetation coverage of the Southern dump, Western A dump, Inner dump and Western B dump increased from 0.29 to 0.68, 0.34 to 0.59, 0.5 to 0.76, and 0.46 to 0.54, respectively. The increase of the global Moran's Index from 0.80 to 0.91 indicated that the spatial agglomeration was greatly influenced by anthropogenic activities from 1992 to 2015. The local Moran's Index showed that the vegetation fractional coverage of the whole stage was mainly high-high clustering and low-low clustering in 2015, and the vegetation fractional coverage of the dumping sites changed from the original low-low clustering to high-high clustering from 1992 to 2015. The area was heavily affected by both mining and reclamation, the vegetation fractional coverage of the dump site was significantly improved after reclamation.

Temporal and spatial change of land use in a large-scale opencast coal mine area: A complex network approach

Large-scale opencast coal mining results in the severe destruction of original ecosystems, as well as changes in land use. The complex network approach can be helpful for understanding the complex land use process. In this study, the complex network approach was used to analyze the land use change in the Pingshuo opencast coal mine area in the Shanxi province of China. Using six periods of land use data from 1986 to 2015, a complex network of land use change of five stages was constructed. The values of node degree, betweenness, and average shortest path in the network were calculated to identify the key land use type, the transformation process of different land use types and to discuss the stability of land use systems. Moreover, the main parts of complex networks were selected to evaluate the temporal and spatial changes of land use processes. From 1986 to 2015, with the dual influence of coal mining and high-speed urbanization, the amount of agricultural land decreased; in contrast, the amount of construction land, industrial and mining area land generally increased. Agricultural land was the main output land type, and construction land and industrial and mining area land were the main input land types. Cultivated land, forest land, and grassland were the key land use types during land processes from 1986 to 2009. Cultivated land, forest land, stripping areas and dumping areas became the key land types from 2009 to 2013, and from 2013 to 2015, cultivated land, forest land, and transportation land became the key land types. Large-scale opencast mining activities severely affect land use change. The overall stability of the land-use system was poor, and the system had the worst stability because of the intensification of mining activities from 2009 to 2013. Local government and coal enterprise should carry out some measures to improve the land use in large-scale opencast coal mine areas, including laying emphasis on land-saving use during mining processes, protecting agricultural land, controlling construction land, strengthening land reclamation, optimizing the use of reclamation land, and using “lease instead of expropriation” to carry out the reform of mined land.

Using computed tomography images to characterize the effects of soil compaction resulting from large machinery on three-dimensional pore characteristics in an opencast coal mine dump

Purpose: The use of heavy machinery in mining areas increases during mining and dumping of waste soils, causing severe soil compaction and potentially affecting soil recovery. This study aimed to capture the features of complex compacted soil pore structure using computed tomography (CT) and to quantify soil pore distribution properties based on Minkowski theory. Materials and methods: A total of 45 cylindrical soil columns were extracted from different soil layer at 5 sampling sites that differed in compaction level in Pingshuo opencast coal mine in Shanxi Province of China. The penetration resistance at these sites ranged from 27.3 to 1023.1 kPa. Three-dimensional reconstruction software VGStudio was used to obtain the morphological characteristics (pore volume density, VD; surface density, SD; mean curvature density, MCD; and Euler number, EN) of soil pores after processing the X-ray scanned image. Results and discussion: Compaction generally reduced VD, SD, and MCD, which ranged from 0.10 to 0.20, 2.23 to 2.80 mm 2 mm −3 , and 10.75 to 15.64 mm mm −3 respectively in undisturbed site P0, whereas, they ranged from 0.02 to 0.07, 0.13 to 0.60 mm 2 mm −3 , and 1.61 to 4.27 mm mm −3 respectively in highly compacted site P4. The three index exhibited the similar trend, and decreased with the increase of compaction level. Soil compaction had positive effects on EN, which was low at the depth of 20- to 40-cm layers but showed an increasing trend with increasing soil compaction level. The value of EN varied from 28,878 to 129,861 in P0, whereas it varied from 1,169,967 to 2,281,998 in P4. Conclusions: All of macroporosity, mesoporosity, and microporosity were significantly affected by heavy machinery compaction, among which macroporosity exhibited the maximum decrease in P4 compared to that in P0 (P0 ranged from 14.2 to 26.4% and P4 ranged from 0.2 to 1.4%). The soil compaction in mining area significantly affected soil properties, thus artificial methods such as fertilizer application and deep tillage were needed.

Reclamation promotes the succession of the soil and vegetation in opencast coal mine: A case study from Robinia pseudoacacia reclaimed forests, Pingshuo mine, China

Robinia pseudoacacia is the dominant tree species in opencast coal mine reclamation in the Loess Plateau, China. Nevertheless, the long-term changes of reclaimed mine soils (RMSs) and vegetation in the reclaimed sites under R. pseudoacacia monoculture forest have not been sufficiently elucidated. In this study, the RMSs physicochemical properties were measured and vegetation (including tree, herb and reserved litter) indexes were surveyed in R. pseudoacacia monoculture forests at 7 reclamation ages (8-, 10-, 13-, 15-, 18-, 23- and 30-year) in the Pingshuo opencast coal mine, China. Adjacent, unreclaimed plot (hereafter called 0-year reclamation plot) was selected as the base line to detect the dynamics of RMSs properties and undisturbed site was chosen to compare with the reclaimed ones. The results showed that, pH (varied from 8.72 to 8.07) and soil bulk density (BD) (ranged from 1.62 to 1.36 Mg m−3) decreased along reclamation chronosequence. In contrast, soil organic matter (SOM, differed from 3.97 to 35.17 g kg−1), total nitrogen (TN, differed from 0.23 to 1.19 g kg−1) and available potassium (AK, ranged from 62.87 to 233 mg kg−1) were found to increase sharply (P < 0.05) in the initial phase of reclamation and tended to be stagnant in the subsequent stage. Moreover, available nitrogen (AN, varied from 7.07 mg kg−1 to 82.20 mg kg−1) was observed to follow a concave curve along reclamation chonosequence. Total phosphorus (TP, differed from 0.48 g kg−1 to 0.60 g kg−1), available phosphorus (AP, varied from 4.33 mg kg−1 to 8.3 mg kg−1) and total potassium (TK, varied from 14.23 g kg−1 to 19.37 g kg−1), however, fluctuated at steady conditions after reclamation and remained the undisturbed levels throughout the reclamation stages. The duration required to attain the nutrient level in undisturbed soils was speculated 10 years of reclamation in the Pingshuo mine. Tree indexes (i.e., diameter at breast height, height, canopy area, biomass and biomass density) increased with the duration of reclamation. Herb indexes (including height, coverage percentage and biomass density), however, followed inversed U functions. Conversely, reserved litter biomass decreased progressively over time. Vegetation indexes were found significantly correlated with SOM, TN, AN and AK (P < 0.05). Overall, R. pseudoacacia monoculture forests markedly ameliorated both soil and vegetation succession in the Pinshuo dumps.

Characteristics of labile organic carbon fractions in reclaimed mine soils: Evidence from three reclaimed forests in the Pingshuo opencast coal mine, China

The reclamation of discarded spoils has the potential to stimulate carbon (C) sequestration in reclaimed mine soils (RMSs). Nevertheless, to date the temporal dynamics of labile organic C fractions have not been sufficiently elucidated in RMSs. In this study, soil organic carbon (SOC) and labile organic C fractions, including microbial biomass organic C (MBC), easily oxidizable organic C (EOC) and dissolved organic C (DOC), were determined in Robinia pseudoacacia monoculture forests (reclamation periods of 0, 8, 10, 13, 15, 18 and 30years), Pinus tabuliformis forests (reclamation periods of 0, 10, 19, 23 and 25years) and Ulmus pumila forests (reclamation periods of 0, 18, 20 and 22years) situated on RMSs in the Pingshuo opencast coal mine, China. Changes in labile organic C fractions within the soil profiles (0–100cm) were also identified at the 18- or 19-year plots under the three monoculture forests. Our results showed that, SOC and labile organic C fractions, together with soil microbial quotient (SMQ) and C management index (CMI), increased with time since reclamation, indicating that the quality of RMSs improved over time after initial reclamation under the three forest types. R. pseudoacacia significantly increased the accretion of SOC and EOC in the early stage of reclamation while P. tabuliformis accelerated the accumulation of the MBC fraction. Results for U. pumila indicated that this species had a better ability to store C in RMSs 10years or more after reclamation. SOC and labile organic C fractions both had S-shaped distributions within the soil profiles (0–100cm), with the 0–20cm layer recording the highest values (P<0.05). Labile organic C fractions were closely associated and correlated with soil physicochemical properties; our results also showed that nitrogen played an important role in the development of labile organic C fractions. Overall, reclamation accelerated the accretion of both SOC and labile organic C fractions, results of which varied among the reclaimed forests.

Soil organic carbon and nitrogen pools in reclaimed mine soils under forest and cropland ecosystems in the Loess Plateau, China

Reclamation of opencast coal mine significantly ameliorates the degraded edaphic characteristics. The long-term changes of carbon (C) and nitrogen (N) pools in reclaimed mine soils (RMSs) in the Loess Plateau, China, have not been sufficiently elucidated. In this study, six types of reclaimed forest stands (with similar reclamation age between 22 and 25-year) and three age chronosequence reclaimed croplands (2-, 7-, 18-year of reclamation) were identified in Pingshuo opencast coal mine, Shanxi Province, to determine SOC and N pools in RMSs. Adjacent, undisturbed sites of forest and cropland and unreclaimed plots were selected as references as well. The results showed that 22–25 years after reclamation, SOC and N pools differed significantly among forest RMSs, ranging from 11.66 to 69.10Mgha−1 and 945.14 to 3145.83kgha−1, respectively, among which R. pseudoacacia–P. tabulaeformis forest had the greatest SOC and N pools and sequestration rates. Moreover, SOC and N pools in cropland RMSs increased across reclamation age chronosequence, ranging from 6.44 to 19.49Mgha−1 and 666.55 to 1554.73kgha−1, respectively. The sequestration rates of SOC and N in cropland RMSs followed polynomial function across age chronosequence. C:N ratio varied among plots and tended to be higher in RMSs under the mixed forest of trees. SOC and N pools were negatively correlated with soil pH. Our study indicated that SOC and N pools could be improved across age chronosequence through well managed vegetation restoration. R. pseudoacacia–P. tabulaeformis mixed forest and H. rhamnoides monoculture forest could be effective reclamation patterns to restore SOC and N pools in Pingshuo opencast coal mine.

Reclamation patterns vary carbon sequestration by trees and soils in an opencast coal mine, China

Reforestation is often recommended for ecological restoration in mining areas because of tree's high stand-level productivity and satisfied carbon (C) and other nutrient sequestration objectives. However, the C sequestration efficiency of different plantation patterns or different tree species is rarely understood. In order to get insight of the C sequestration efficiency by trees and soils of different reclamation patterns in Pingshuo opencast coal mine, Shanxi Province, China, three different reclamation patterns (developed for 17years) at three permanent fixed plots, broadleaf mixed forest: R. pseudoacacia-U. pumila-A. altissima (Plot code: BM), broadleaf conifer mixed forest: R. pseudoacacia-P. tabulaeformis (Plot code: BC) and broadleaf monoculture forest: R. pseudoacacia (Plot code: BR), were selected and investigated. The results showed that tree volumes and biomass differed significantly after 17years' succession, from 21.58m3 and 36.02Mgha−1 of the broadleaf monoculture forest (BR) to 37.20m3 and 48.73Mgha−1 of broadleaf conifer mixed forest (BC). Accordingly, tree C and litter C were observed higher in BC (24.37 and 2.26Mgha−1) than BM (19.25 and 1.15Mgha−1) and BR (18.01 and 1.31Mgha−1). Herb C, however, was observed lower in BC (0.02Mgha−1) than BR (0.25Mgha−1) and BM (0.24Mgha−1). C sequestrated in soil organic matter varied in the order: BC (172.16Mgha−1)>BM (73.79Mgha−1)>BR (51.59Mgha−1) and the top layer (0-20cm) C contributed a large portion (varied from 37% in BC to 53% in BM) of the total soil C. Consequently, BC sequestrated the highest total C (198.81Mgha−1) by plant, litter and soil, followed by BM (94.43Mgha−1) and BR (71.16Mgha−1). In regard to the total C distribution, a major portion of the total C consisted of soil C (varied from 72.49% in BR to 86.60% in BC). Overall, this study indicated that mixed forest facilitated sequestrating more C than pure forest, and the broadleaf conifer mixed forest: R. pseudoacacia-P. tabulaeformis not only accumulated more plant biomass but also accelerated the soil C sequestration which may be suggested as the more suitable pattern for the opencast coal mine reclamation in the region of eastern Loess Plateau of China.

Dynamic Parameters of Plant Communities Partially Reflect the Soil Quality Improvement in Eco‐Reclamation Area of an Opencast Coal Mine

AbstractThe influence of soil physicochemical properties and the relationship between the plant community and edaphic factors have been studied through monitoring the community dynamic parameters and analyzing the soil properties from four plant plots at the Pingshuo opencast coal mine eco‐reclamation area. The results are obtained as follows: (1) the law of the quantity variation of total N and available K is affected by the different kinds of plant configuration mode. It is Robinia pseudoacacia + Pinus tabuliformis (SIV) &gt; R. pseudoacacia (SV) &gt; R. pseudoacacia + P. tabuliformis (SI) &gt; R. pseudoacacia + Ulmus pumila + Ailanthus altissima (SIII). The quantity is close to or exceeds the level of the original geomorphology. The average content of available N has the following order: SIV &gt; SI &gt; SIII &gt; SV; the average content of available P SV &gt; SIII &gt; SIV &gt; SI, both are far below the level of the original geomorphology; pH SIV &lt; SIII &lt; SI &lt; SV; bulk density SI &lt; SIV &lt; SV &lt; SIII, moisture content SIV &gt; SIII &gt; SI &gt; SV; in the soil layer of 20–40 cm, except the available P, other physicochemical factors are in accordance with the factors of the surface soil; (2) the population average density, height and diameter at breast height (DBH) have no obvious relevance with the average density of the stumpage; (3) the average density, height, and DBH of R. pseudoacacia are closely related to pH and the content of available N and available P and all the index can be fitted by the equation of linear regression of the edaphic factors mentioned above. The principal component analysis shows that the magnitude of the impacts of three kinds of edaphic factors on the R. pseudoacacia population has the following order: pH &gt; available N &gt; available P. The average density of U. pumila is closely related to the moisture content of the soil. This regression model can be used to direct the cultivation and propagation of R. pseudoacacia and U. pumila population at the mine eco‐reclamation area.

Soils development in opencast coal mine spoils reclaimed for 1–13 years in the West-Northern Loess Plateau of China

Soil development is the key process of mine spoil reclamation. To investigate the effects of different plant species and reclamation time on the soil development, 9 plots in the reclaimed spoils of Pingshuo opencast coal mine in Shanxi, China were established and the physical, chemical and microbiological properties of the soils were analyzed. The results showed that, soil bulk density and field capacity in plots with longer reclamation time were statistically different from plots with younger vegetation in both the 0–20 cm and 20–40 cm soil layers. Accordingly, values of organic matter and available nitrogen levels showed a significant increase in both 0–20 cm and 20–40 cm depth with reclamation time increasing and the top layer marked higher value except for some individual data. The organic matter in plot 8 in 0–20 cm depth with 13-year old vegetation reached 9.45 g kg−1, about 2.5-, 2.0- and 3.1-fold higher than the plots of 1-, 3- and 4-year old vegetation respectively. Total microbial amount showed a positive correlation with contents of organic matter which reached 1436.72 × 105 g−1 in plot 8 with 13-years old vegetation, about 11.3-fold greater than plot 1 of 1-yr old vegetation. Plots planted with sea buckthorn (Hippophae rhamnoides ssp. sinensis) singly or mixed with other species tend to develop better soil aggregation and microbiological properties than other plots, which may be due to its particular biological characteristics, developed root system and high growth rate in the first 4–6 year and 8–10 year, indicating that sea buckthorn may be a good species choice for activating soil development in the early stage of reclamation.

99/03465 Characterization of hydrothermally dried low-rank coals: Walsh, D. E. et al. Miner. Metall. Process., 1999, 16, (1), 48–56

Reclamation of opencast coal mine significantly ameliorates the degraded edaphic characteristics. The long-term changes of carbon (C) and nitrogen (N) pools in reclaimed mine soils (RMSs) in the Loess Plateau, China, have not been sufficiently elucidated. In this study, six types of reclaimed forest stands (with similar reclamation age between 22 and 25-year) and three age chronosequence reclaimed croplands (2-, 7-, 18-year of reclamation) were identified in Pingshuo opencast coal mine, Shanxi Province, to determine SOC and N pools in RMSs. Adjacent, undisturbed sites of forest and cropland and unreclaimed plots were selected as references as well. The results showed that 22–25 years after reclamation, SOC and N pools differed significantly among forest RMSs, ranging from 11.66 to 69.10 Mg ha−1 and 945.14 to 3145.83 kg ha−1, respectively, among which R. pseudoacacia–P. tabulaeformis forest had the greatest SOC and N pools and sequestration rates. Moreover, SOC and N pools in cropland RMSs increased across reclamation age chronosequence, ranging from 6.44 to 19.49 Mg ha−1 and 666.55 to 1554.73 kg ha−1, respectively. The sequestration rates of SOC and N in cropland RMSs followed polynomial function across age chronosequence. C:N ratio varied among plots and tended to be higher in RMSs under the mixed forest of trees. SOC and N pools were negatively correlated with soil pH. Our study indicated that SOC and N pools could be improved across age chronosequence through well managed vegetation restoration. R. pseudoacacia–P. tabulaeformis mixed forest and H. rhamnoides monoculture forest could be effective reclamation patterns to restore SOC and N pools in Pingshuo opencast coal mine.