Spatiotemporal variation pattern of production-living-ecological space and land use ecological risk and their relationship analysis: a case study of Changzhi City, China.

With the rapid development of mining, more and more cities faced the trade-off between ecological protection and large-scale mining. Assessment of production-living-ecological space transformation and land use ecological risk can provide a scientific guidance for land use management and risk control. This paper focused on a resource-based city, Changzhi City in China, using RRM model and elasticity coefficient to analyze the spatiotemporal characteristics of the production-living-ecological space evolution and land use ecological risk change, and measured the responsiveness of land use ecological risk to space transformation. The results showed the following: (1) From 2000 to 2020, production, living, and ecological spaces showed increased, decreased, and stable conditions, respectively. (2) The level of ecological risk showed an increasing trend from 2000 to 2020; the growth rate in the last 10 years was significantly lower than that in the first 10 years which was due to policy induced; the changes of ecological risk levels in each district and county were insignificant. (3) The elasticity coefficient from 2010 to 2020 became significantly less than that of the previous 10 years. The impact of the production-living-ecological space transformation on ecological risk was significantly reduced and the influencing factors of land use ecological risk were more diversified. However, Luzhou District still had a high level of land use ecological risk, which needs to pay more attention and be taken seriously. Our study provided guidance for ecological protection, rational land use, and territory development plan in Changzhi City, and also can be used as a reference in other resource-based cities.

Investigating the trade-offs between the supply and demand for ecosystem services for regional spatial management.

Understanding the supply and demand characteristics of ecosystem services (ESs) and their trade-offs is the basis for effective ecosystem management and the improvement of human well-being. However, current management practices based on the trade-offs between the supply and demand for ESs remain limited. This study aimed to integrate ES trade-offs into regional spatial management. With Changzhi, China, as the study area, this study evaluated the supply, demand, and trade-offs of food provision, water conservation, soil retention, and carbon sequestration by linking multi-source data and using spatial analysis tools, including the InVEST model, ArcGIS, and GeoDA. Based on the trade-offs and importance of different ecological functions, we constructed an urban spatial management framework and proposed recommendations for optimization in different management zones. The results showed that (1) the supply and demand for multiple ESs exhibited spatial heterogeneity. Except for water conservation, the supply of other ESs met the demand of the city, but there were still obvious deficits in some regions. (2) In terms of the ES supply, there were trade-offs between food production and other ESs, and synergies existed among water conservation, soil retention, and carbon sequestration. In terms of the ES demand, the four ESs exhibited synergistic relationships. In the cluster analysis, ES supply and demand were divided into four ES bundles, respectively. (3) The spatial mismatch of ESs in the sub-watersheds of the study area was obvious. The ESDR coldspots for the four ESs were primarily located in the urban built-up areas in the central and southern regions of the city. The ESDR hotspots of soil retention and carbon sequestration were mainly distributed in the eastern and northwestern regions of Changzhi, which are less urbanized. There were few ESDR hotspots for food production and water conservation. (4) Based on the regional spatial management framework, Changzhi was divided into ten zones, including extremely important, moderately important, important, supply-demand risk management, soil erosion management, and high food production areas. The results and conclusions of this study provide a basis for spatial planning and ecosystem management.

Research on Adaptive Management of the Social-Ecological System of a Typical Mine-Agriculture-Urban Compound Area in North Shanxi, China.

The mine-agriculture-urban compound area formed under the combined effects of natural conditions, mineral resource endowments, and historical development is affected by severe man-made disturbances, and faces a prominent contradiction between economic development and ecological protection. Guiding the future development is an urgent problem in this region. This research used image data, logical reasoning, and empirical analysis, based on social and economic statistics and land-use data, to analyze the typical characteristics and problems of the social-ecological system in the mine-agriculture-urban compound area. Moreover, we identified future directions for the region guided by policy documents and built a philosophy framework for sustainable development and management of the region based on the concept of adaptability. The results showed the following: (1) At present, the output value of the coal industry accounts for 84.10% of the total regional output value, severely disturbing its social-ecological system, which needs to be protected and restored under human guidance and management. (2) The future development of this region depends on the one hand on green mining, and on the other hand, it is necessary to fully tap the potential of arable land and livestock farms to develop efficient and intensive agriculture. (3) The key contents of the social-ecological system management of the mine-agriculture-urban compound area include resolving the contradiction between development and protection, ensuring development, optimizing industrial structure, and safeguarding public interests. In conclusion, this research can expand the connotation and application scope of adaptive management and provide a reference for such areas facing the prominent contradiction between development and protection.

Succession law and model of reconstructed soil quality in an open-pit coal mine dump of the loess area, China.

Studying the change laws of reconstructed soil quality and constructing succession models are the main components and tools of reconstructed soil quality evaluation for the supervision and management of reconstructed soil. However, the evaluation and management system of reconstructed soil quality suitable for the loess area needs to be improved. This paper aimed to clarify the succession law of reconstructed soil in an open-pit coal dump in the loess area on the temporal scale and to construct a succession model of reconstructed soil quality to evaluate and manage reconstructed soil. The Pingshuo coal mine, a representative open-pit coal mine in the loess area, is the study area. Field investigation and sampling, time-space substitution, and the combination of qualitative and quantitative research methods were used. The reconstructed soil quality succession model was constructed based on the soil quality index method. Results: (1) As the reclamation period increased, the physical and chemical properties of reconstructed soil significantly improved, and reconstructed soil quality generally reached the quality of the original landform after approximately 15 years of reclamation. However, after long-term reclamation, soil physical properties still limited the improvement of reconstructed soil quality to a certain extent. (2) After long-term reclamation, the difference in reconstructed soil quality between layers gradually decreased, and the reconstructed soil condition of the 0-10 cm soil layer was obviously better than that of the other layers. (3) We quantitatively constructed and verified the reconstructed soil quality succession model that is suitable for the loess area, which can be used in conjunction with adaptive management for the evaluation and management of reconstructed soil in the loess area. In conclusion, this study is of great significance to meet the real needs of dynamic evaluation and management of reconstructed soil quality in the loess area and to enrich the soil evaluation and management system at home and abroad.

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.

Deciphering the origin and controlling factors of mercury in reclaimed soils: a case study in Pingshuo opencast coalmine of 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 50 µg kg-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 (0-10 cm) 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.

A new soil sampling design method using multi-temporal and spatial data fusion.

The distribution of soil pollutants is receiving increasing attention. The accurate determination of the soil pollution distribution in an area is becoming more important. To date, many soil quality surveys have already been carried out in China, and the use of these surveys to reflect soil pollution is worth examining. This article provides an example of the application of combined two-phase data to assess soil contamination in a region. Based on data acquired during two soil sampling phases in 2005 and 2015, we chose a typical watershed in southeast China as the study area. We analysed the data using spatial interpolation analysis, compared the results, and extracted points to perform point combination based on site conditions. Ultimately, these analyses allowed us to develop a new method involving the use of multi-period data to evaluate the soil quality on a regional scale. In the ten years from 2005 to 2015, apparent changes in soil pollution occurred. We found that the area with no change in soil pollution accounts for 46.98% of the total basin and the area demonstrating a soil pollution increase accounts for 47.25% of the total basin, while the area exhibiting a soil pollution reduction only accounts for 5.78% of the whole area. The average accuracy of the combined points increased to 89% from 76 and 81%. The analysis of the land-use types and spatial locations during the two periods revealed no direct relationship between the soil contamination changes and the changes in the total number of land-use types, but a correlation was observed with the intensity of human activities at the spatial locations. This paper proposes a new method for the spatial assessment of soil pollution based using multiple periods of existing data on the above analysis.

Spatiotemporal dynamic differences of energy-related CO2 emissions and the related driven factors in six regions of China during two decades.

Carbon neutrality lays out a grand blueprint for carbon emission reduction and climate governance in China. How to reduce energy consumption is the key to achieving this goal. The economic development and energy consumption show a very large gap at the provincial level, and this paper divides China into six regions (North, Northeast, East, Mid-South, Southwest, and Northwest) and analyzes the dynamic changes and reveals the driving factors that have affected CO2 emission changes from 1997 to 2017. Then, the driving forces including energy intensity, energy structure, energy efficiency, economic activity, and population scale were discussed employing the logarithmic mean Divisia index (LMDI) based on provincial panel data. The results show that CO2 emissions from energy consumption show an upward trend, from 4145 Mt in 1997 to 13,250 Mt in 2017, with an annual average growth rate of 1.06%; coal consumption is the main source of CO2 emission. The regions with the highest proportion of CO2 emissions are the East and North, which account for 50% of total emissions. China's CO2 emissions from energy consumption, coal consumption, and output have shown significant spatial autocorrelation at the provincial scale. According to coal consumption, energy consumption CO2 emissions are divided into three stages: phase I (1997-2002), the increase in CO2 emissions in six regions was attributed to significant and positive impacts of energy intensity, economic activity, and population scale, the effects of which exceeded those of the energy structure and energy efficiency; phase II (2003-2012), the economic activity effect on CO2 emissions was highest in the East region, followed by the North and Mid-South regions; phase III (2013-2017), the East, Mid-South, and Southwest regions of China were dominated by the positive effects of energy intensity, economic activity, and population scale. The major driver of CO2 emissions is economic activity; the energy efficiency effect is an important inhibitory factor. Regional economic development and energy consumption in China are unbalanced; we conclude that differentiated emission reduction measures should be of particular concern for policymakers.

Detection of soil physical properties of reclaimed land in open-pit mining area: feasibility of application of ground penetrating radar.

In order to obtain the typical soil physical properties of reclaimed land more quickly and accurately, the South Dump of the China Coal's Antaibao Open-Pit Mine in Pingshuo was focussed on in this paper, and ground penetrating radar (GPR) technology was utilized to detect the soil physical properties of reclaimed land in the mining area. The soil profile sampling and GPR detection methods were used to acquire the data. The gravel content of surface soil was analyzed by counting the number of isolated gravel signals in GPR images. The change of effective soil thickness was analyzed by establishing the fitting relationship between calibration depth and GPR image depth. The Topp's model was validated by comparing its inversion with the measured soil volumetric water content. And the Topp's model was further validated by the soil volumetric water content obtained from the Topp's model and which obtained from the wave velocity inversion. The results are as follows: (1) Based on the number of isolated gravel signals in GPR images, we could qualitatively analyze the gravel content of surface soil reclaimed in the mining area. As the number of isolated gravel signals was greater, the gravel content of the surface soil was higher. (2) Using the known relative permittivity, electromagnetic wave velocity, and soil volumetric water content, the calibration depth and the reflection depth of the target (calibrator) of the GPR images were segmented, and the correlation between them is high. The fitting relationship (R2) of each segment was higher than 0.940, and the average value of the five-segment R2 was 0.966, which indicated more accurate detection of the effective soil thickness of the reclaimed land in the mining area. (3) GPR could be used to detect the soil volumetric water content of reclaimed land in mining area, and Topp's model was used for calculation of soil volumetric water content. The average deviation rate between the values from Topp's model and the measured values was 12%, and the average absolute value of the difference was 2%. In summary, the benefits of using GPR to detect soil physical properties of reclaimed land in mining area are as follows: (1) GPR can be used to detect soil layer thickness and surface gravel content faster and more accurately. (2) Topp model can also be used to calculate the soil moisture content of non-natural deposits such as reclaimed land in mining area.

Delimitation of supervision zones based on the soil property characteristics in a reclaimed opencast coal mine dump on the Loess Plateau, China.

Supervision zones in a reclaimed coal mine refer to regions where soil properties are being slowly restored but further management is still urgently needed. The important roles of supervision zones in guiding the ecological restoration of degraded mining areas have been widely recognized, but the delimitation of supervision zones needs further examination. To delineate supervision zones for the restoration of poor soil properties, the soil available phosphorus (SAP), soil available potassium (SAK), soil total nitrogen (STN), soil organic matter (SOM), soil particle fractal dimension (SPD), soil electric conductivity (SEC), and soil pH (pH) at a depth of 0-20 cm were measured in a reclaimed dump in the Antaibao coal mine on the Loess Plateau of China. The spatial distribution of the soil properties was analyzed using geostatistical analysis, a fuzzy c-means clustering algorithm, and pedodiversity analysis. Then, the supervision zones were delimited based on the spatial characteristics of the reclaimed soil properties. The results revealed the following: (1) reclaimed soil in the study area was clustered into eight classes, and each soil class had one or more well-recovered soil properties, except for class I. Areas covered with only class I soil were delimited as poor-soil property regions. (2) The spatial distribution of the pedodiversity indexes of the reclaimed soil classes showed obvious aggregation characteristics, with extremely low values occurring mainly in the northeast and south of the study area. Two zones with low values of the Shannon index (H) were delimited as low-pedodiversity regions. (3) Four supervision zones with poor land reclamation effects were delimited based on the analysis of the poor-soil property regions and low-pedodiversity regions, and precise reclamation measures, including crop rotation, fertilization, neutralization, irrigation, and plowing, were proposed for each zone to improve the quality of the reclaimed soil.

Analysis of differences in chemical properties of reconstructed soil under different proportions of topsoil substitute materials.

The purpose of this study was to evaluate the soil substitutes in land reclamation following mining activities. This study revealed different reconstructed soil materials have different effects on the chemical properties of reconstructed soil and explored the appropriate proportions of reconstructed soil materials. Using topsoil, coal gangue, fly ash, and rock and soil stripping material from the Shengli Mining Area of Inner Mongolia in China as raw materials, potting experiments were carried out according to different proportions. The variance analysis method was used to analyze the difference in the soil pH values, soil organic matter (SOM) content, soil total nitrogen (STN) content, soil available phosphorus (SAP) content and soil available potassium (SAK) content of the reconstructed soil, and the reasons for the difference were discussed. The results showed that in the treatment group where the topsoil substitute material was coal gangue, when the coal gangue content was 30%, 40%, and 50%, the pH values of reconstructed soil were lower than that of the control scheme. When the coal gangue content exceeded 10%, the soil nutrient status was obviously improved. In the treatment group where the topsoil substitute material was fly ash, the chemical properties of reconstructed soil tended to deteriorate. In the treatment group where the topsoil substitute material was rock and soil stripping material, when the content of rock and soil stripping material exceeded 20%, the chemical properties of reconstructed soil were mostly better than those of the control scheme. The study of the different proportions of coal gangue, fly ash, and rock and soil stripping material as topsoil substitute materials provide support for reclamation work in mining areas where topsoil is scarce, as well as a reference for ecological restoration projects in grassland open-pit mining areas around the world.

The addition of degradable chelating agents enhances maize phytoremediation efficiency in Cd-contaminated soils.

Chelating agent-induced phytoremediation is a viable approach to completely remove heavy metals from soil. However, little attention has been paid to the interaction mechanisms between the concentration of the chelating agent and the application time on the physiological and biochemical properties of soil and plants. In this study, five chelating agents, namely ethylenediamine tetraacetic acid (EDTA), diethylenetriacetic acid (NTA), tetrasodium N, N-diacetate (GLDA), aspartate dibutyric acid ether (AES), and iminodisuccinic acid (IDSA), were used to support phytoremediation with maize and to explore the removal effect of Cd in soil. The results showed that chelating agent concentrations of 9 mmol kg-1 significantly reduced the biomass of maize. Treatment with AES at a dose of 6 mmol kg-1 significantly increased aboveground biomass, reaching a maximum of 0.92 g pot-1 in all treatments. At an AES concentration of 6 mmol kg-1, the highest shoot and root Cd levels of 7.79 and 9.86 mg kg-1, respectively, were observed, which were 3.05 and 1.60 times higher than those of the control. Total Cd extraction followed the order AES (6 mmol kg-1) > GLDA > NTA > EDTA > IDSA (3 mmol kg-1). Chelating agent treatment significantly increased the activity of antioxidant enzymes and promoted plant growth. The self-degradation of AES significantly reduced soil pH, increased soil Cd activity, and promoted Cd uptake and transportation in maize.

Environmental impact of mining-associated carbon emissions and analysis of cleaner production strategies in China.

In recent years, concern has been increasing regarding the carbon emissions generated by mining activities. China is an extremely large coal producer (3695 Mt/2015) and consumer (3698 Mt/2015), and Shanxi Province (i.e., a major coal-producing province in China) is a crucial element in China's energy conservation and emission reduction goals. In this study, the Pingshuo mining area (PMA) in Shanxi Province was chosen as a case to analyze the dynamic changes in carbon emissions based on the Intergovernmental Panel on Climate Change (IPCC) method, and the factors influencing carbon emissions were analyzed via the IPAT equation. Carbon emission sources in opencast mines mainly included fuel and explosive use, coal mine methane escape, coal and gangue spontaneous combustion, and electricity consumption. The carbon emission of the PMA increased from 4 × 104 Mg in 1986 to 1.05 × 106 Mg in 2015, with an average annual increase of 11.64%. In the PMA, 4.71 × 106 Mg of carbon emissions from fuel consumption accounted for 41.79% of carbon emissions, and 5.26 × 106 Mg of carbon emissions from methane emissions accounted for 46.66%. Carbon emissions from explosives and electricity use were 4.1 × 105 Mg and 8.8 × 105 Mg, respectively. In this mining area, the factors influencing carbon emissions included population, GDP, and coal output. The results of this study not only provide a reference for cleaner production in mining areas but also lay a foundation for the study of global opencast coal mining carbon emissions.

Spatial distribution of soil bulk density and its relationship with slope and vegetation allocation model in rehabilitation of dumping site in loess open-pit mine area.

Studies of soil bulk density (BD) spatial variations of land reclaimed after mining have become a focus of land reclamation and ecological restoration research. However, there have been few studies on the relationship among the reconstructed BD, terrain conditions, and vegetation growth. We examined the southern dumping site of the Pingshuo Antaibao open-pit coal mine located in a loess area in China. Field sampling data, digital elevation models (DEMs), and high-definition images were obtained, and indoor testing, geostatistics, and inverse distance weighting (IDW) were applied. This paper aims to analyze the spatial distribution law of the reconstructed BD and focus on its relationship with slope and vegetation allocation models. We demonstrated that (1) BD increased with soil depth and varied moderately within each layer. (2) The BD variation amplitude of the top 0-20-cm soil layer in both the east-west and south-north directions was small and more similar in the east-west direction than in the south-north direction, which was affected by herbaceous root systems. In the next four layers from 20 to 60 cm, the variation in BD in the east-west direction was far larger than that in the south-north direction, which was affected by vegetation classification. (3) On the whole, BD decreased with increasing slope, but when the slope was between 0° and 21°, BD exhibited a specific change law. (4) From the perspective of vegetation classification, the orders of magnitude of BD in the 0-20-cm and 20-60-cm layers differed. Overall, BD in areas vegetated with Korshinsk Peashrub was the lowest, and BD was moderate in areas with mixed vegetation, while BD was the highest in areas without vegetation or only vegetated with Black Locust. The mixed grass-bush-tree or bush-tree mode attained the best effect in regulating BD. These results can improve the basic principles of land reclamation in mining areas and provide a basis for further optimizing land reclamation technology in practice.

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.

The effect of combined ecological remediation (plant microorganism modifier) on rare earth mine wasteland.

Due to the vegetation destruction and soil desertification caused by excessive exploitation at Ganzhou ion-type rare earth mine in the mid-1980s, it is essential to carry out ecological remediation. The symbiotic mycorrhiza formed by the developed perennial ryegrass (Lolium perenne L.) roots infected with arbuscular mycorrhizal fungi (AMF) can significantly improve the growth and resistance of plants. In this study, the combination of symbiotic mycorrhiza and soil modifier was used to construct the ryegrass-AMF-soil modifier combined remediation technology, which achieved effective ecological remediation of soil tailings. The orthogonal experiment of soil modifier showed that the most efficient formula for ryegrass biomass, soil organic matter, soil alkaline hydrolysis, soil available phosphorus, and soil pH was 5 g/kg sepiolite, 3 g/kg chicken manure, 2 g/kg humic acid, and 2 g/kg biochar (A4B3C3D3), and chicken manure (B), humic acid (C), and biochar (D) had significant effects on the improvement of ryegrass biomass, soil organic matter, soil alkaline nitrogen, and soil available phosphorus. Sepiolite (A) had a significant improvement in soil pH. Furthermore, the AMF infection results indicated that Glomus moss (G.m.) had higher affinity with ryegrass. The T4 treatment-combined remediation using G.m. inoculation had the most significant effect on ryegrass growth; plant height increased by 39.19% compared with T1 treatment-inoculation using G.m. Under combined remediation, soil pH, organic matter, alkali nitrogen, and effective phosphorus content also significantly improved after combined treatment. Under G.m. inoculation treatment (T4 treatment), the soil nutrient content reached the three criteria of the soil nutrient grading standard.

Heavy metal concentrations of soils near the large opencast coal mine pits in China.

Mining is a common industrial activity and significant source of soil heavy metal (HM) pollution. However, nearly all studies on the effects of mining activities on soil environmental quality have entailed field monitoring of small regions or bibliometric analyses. This study therefore investigated the pollution of surface soils surrounding 135 large opencast coal mining pits in China. A total of 1772 surface soil samples were collected, and the concentrations of eight major HMs were determined. The HM concentrations in this study were relatively lower than the published HM concentrations of coal mine soils from 50 typical Chinese coal mines. However, pollution assessments indicated that Cd, Cu, and As concentrations were concerning. Significant correlations existed between all of the HMs and mining pit area (p < 0.01), as well as between the Pb and Zn concentrations and direction (p < 0.05). Climate conditions had large influences on the HM concentrations. The concentrations of all studied HMs, except for Ni, were highest in Anthrosols and lowest in hydromorphic soils. The concentrations of all HMs, except for Hg, in land use types showed a descending trend of cultivated land > garden plot > grassland. Significantly negative correlations (p < 0.01) between all HM concentrations and elevation were observed. Cr, Zn, and Ni were significantly and positively correlated with the slope, and no HMs, except Cr, showed significant correlations with the parcel area. This paper provides insights for the policymakers regarding soil pollution control and management strategies near coal mine pits.

Effects of mycorrhizae and water conditions on perennial ryegrass growth in rare earth tailings.

Mycorrhizal symbioses, which include plant roots and arbuscular mycorrhizal fungi (AMF), can significantly enhance plant resistance and promote the absorption of soil nutrients by plants. A greenhouse experiment was conducted to investigate the effects of three AMF species (Glomus mosses, Glomus etunicatum and Glomus versiforme) on the height, biomass, malondialdehyde (MDA) and proline contents and antioxidant enzyme activities of perennial ryegrass (Lolium perenne) under different water supply treatments. Potted experimental soil samples were collected from the abandoned rare earth tailings in Ganzhou, Jiangxi. The results showed that all three AMF species infected ryegrass under the different treatments. Under severe drought stress, G. mosses had the most significant effects on the promotion of ryegrass performance. After inoculation, the height and whole-plant biomass of ryegrass increased by 60.44% and 150%, respectively. In addition, inoculation with AMF significantly reduced the content of MDA and proline in the ryegrass leaves in all water supply treatments except the moderate drought stress treatment, in which there was no effect. The leaf antioxidant enzyme activity was also measured. The results showed that under severe drought stress, inoculation with Glomus mosses significantly increased the activities of CAT and SOD in ryegrass and enhanced the resistance of plants. A possible reason that AMF promotes host plant growth and enhances drought resistance is that AMF directly increases the absorption of soil water and minerals by host plant roots and indirectly improves the physiological metabolism of plants.

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.

The soil chemical properties of reclaimed land in an arid grassland dump in an opencast mining area in China.

Opencast coal mining damages the land in arid grassland mining areas where topsoil is scarce. Restoration of the soil chemical properties is important for land reclamation and the rebuilding of vegetation. We studied a south dump after 4 years of reclamation, a north dump after 8 years of reclamation, and undamaged land to identify changes in the soil profile after mining and reclamation. Variance, correlation, and principal component analyses assessed spatial and temporal differences, and correlations between soil organic matter (SOM), total nitrogen (STN), available phosphorus (SAP), available potassium (SAK), and soil pH (pH) in the 0-40 cm layers. The soil chemical properties were evaluated to support the reconstructed soil profiles and guide soil reconstruction in grassland mining areas. SOM, STN, SAP, and SAK in the south dump were significantly lower than those in the undamaged land. SOM and STN levels in the north dump were lower than those in the undamaged land. SAP and SAK levels in the north dump were higher than those in the undamaged land. Therefore, land reclamation can improve the chemical properties of the reconstructed soil profile in grassland mining areas lacking SAP. Principal component analysis revealed that increasing reclamation years improved the soil chemical quality, and that of the surface soil was better than that of the lower layer. The chemical quality of the soil below 20 cm was consistent. At 0-40 cm, correlations between the soil chemical properties declined from top to bottom, and changed from interdependent to mutually independent; SOM was the core element. The use of topsoil and coal gangue to construct soil profiles can improve the soil chemical properties and resolve the difficulties of land reclamation caused by surface soil scarcity and droughts.