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

Tree-level landscape transitions and changes in carbon storage throughout the mine life cycle

Opencast mining activities destroy native vegetation, directly impacting the carbon sequestration capacity of the regional ecosystem. Restoring tree species have significant impacts on carbon storage. However, changes in carbon storage across tree-level landscape and the impact of tree-level landscape transitions on carbon storage remain poorly described in the literature, and this information is urgently needed to support management decisions. In this study, we combined field data and remote sensing techniques to create field data-driven maps of the tree-level landscape. This enabled the assessment of carbon storage and quantification of the impact of tree-level landscape transitions on carbon storage. We founded that carbon storage rises in initial/stable stages, decreases in development stage during mining expansion and reclamation. The choice of restoration tree species significantly influenced carbon storage. Pinus tabuliformis-R. pseudoacacia accumulated more carbon storage, making it a more suitable model for ecological reclamation of Pingshuo opencast mine. Furthermore, changes in carbon storage are influenced by land-use policies. Land-use policies and reclamation efforts counterbalance carbon loss associated with construction. Various tree-level landscape transitions were examined, with Pinus tabuliformis transitions notably affecting carbon storage, offering insights for ecological reclamation planning. Our research provides a reference for carbon storage assessment in opencast mining areas, enhances understanding of carbon storage changes in mining areas, assists in formulating ecological reclamation plans, and contributes to the "dual‑carbon" goals and climate change mitigation.

Monitoring the ecological restoration effect of land reclamation in open-pit coal mining areas: An exploration of a fusion method based on ZhuHai-1 and Landsat 8 data

Land reclamation is a long-term, dynamic process; postreclamation monitoring and management are particularly important, and the use of remote sensing technology is a good way to conduct ecological quality monitoring and evaluations. In this study, we fused ZhuHai-1 and Landsat 8 data; selected the best band combinations to calculate ecological quality indicators such as the inverted red-edge chlorophyll index, modified soil moisture monitoring index, normalized difference built-up and soil index and land surface temperature; and constructed the fusion remote sensing ecological index to monitor the ecological restoration effect of the reclaimed area in Pingshuo, China. The results showed that the inverted red-edge chlorophyll index and modified soil moisture monitoring index had positive contributions, the normalized difference built-up and soil index had a low impact on the ecological quality of the study area, and the land surface temperature had a negative effect on ecological quality. The environment of the reclaimed area was better than that of the surrounding areas where these areas were affected by mining. The mean value of the fusion remote sensing ecological index showed a trend of "rising first, then falling" with increasing reclamation time. The ecological quality of the reclaimed area was best in areas with 20-22 years of reclamation time. The ecological condition of the area has been declining for 25 years or more of reclamation, so it is suitable to apply artificial intervention to ensure good ecological quality. The use of remote sensing technology for monitoring the effects of ecological restoration can provide a reference basis for the targeted and accurate implementation of land reclamation management measures.

Effects of long-term herbaceous plant restoration on microbial communities and metabolic profiles in coal gangue-contaminated soil

The soil microbial diversity in the gangue accumulation area is severely stressed by a variety of heavy metals, while the influence of long-term recovery of herbaceous plants on the ecological structure of gangue-contaminated soil is to be explored. Therefore, we analysed the differences in physicochemical properties, elemental changes, microbial community structure, metabolites and expression of related pathways in soils in the 10- and 20-year herbaceous remediation areas of coal gangue. Our results showed that phosphatase, soil urease, and sucrase activities of gangue soils significantly increased in the shallow layer after herbaceous remediation. However, in zone T1 (10-year remediation zone), the contents of harmful elements, such as Thorium (Th; 1.08-fold), Arsenic (As; 0.78-fold), lead (Pb; 0.99-fold), and uranium (U; 0.77-fold), increased significantly, whereas the soil microbial abundance and diversity also showed a significant decreasing trend. Conversely, in zone T2 (20-year restoration zone), the soil pH significantly increased by 1.03- to 1.06-fold and soil acidity significantly improved. Moreover, the abundance and diversity of soil microorganisms increased significantly, the expression of carbohydrates in soil was significantly downregulated, and sucrose content was significantly negatively correlated with the abundance of microorganisms, such as Streptomyces. A significant decrease in heavy metals was observed in the soil, such as U (1.01- to 1.09-fold) and Pb (1.13- to 1.25-fold). Additionally, the thiamin synthesis pathway was inhibited in the soil of the T1 zone; the expression level of sulfur (S)-containing histidine derivatives (Ergothioneine) was significantly up-regulated by 0.56-fold in the shallow soil of the T2 zone; and the S content in the soil significantly reduced. Aromatic compounds were significantly up-regulated in the soil after 20 years of herbaceous plant remediation in coal gangue soil, and microorganisms (Sphingomonas) with significant positive correlations with benzene ring-containing metabolites, such as Sulfaphenazole, were identified.

Superior improvement on soil quality by Pennisetum sinese vegetation restoration in the dry-hot valley region, SW China

Vegetation restoration is a good way to improve soil quality and reduce erosion. However, the impact of vegetation restoration on soil quality in the dry-hot valley region has been overlooked for many years. This study aimed to reveal the effects of Pennisetum sinese (PS) and natural vegetation (NV) on soil quality and then to explore the feasibility of introducing PS for the vegetation restoration of the dry-hot valley region. The PS and NV restoration areas deserted land evolving from cultivated land (CL) have been established since 2011. The results showed that the soil properties were obviously improved by PS from the dry to wet seasons, except for the soil available phosphorous. The comprehensive soil quality indexes of the three typical seasons (dry, dry-wet, and wet) were determined by using nonlinear weighted additive (NLWA) based on the total dataset, significant dataset and minimum dataset (MDS). The results indicated that the comprehensive minimum dataset soil quality index (MDS-SQI) of the three typical seasons evaluate soil quality well. The soil quality of PS was significantly greater than that of CL and NV (P < 0.05), as shown by the MDS-SQI. Additionally, PS could maintain a stable soil quality in the three typical seasons, while both CL and NV had obvious fluctuations. In addition, the result of the generalized linear mode suggested that the vegetation type had the greatest impact on the soil quality (44.51 %). Comprehensively, vegetation restoration in the dry-hot valley region has a positive impact on the soil properties and quality. PS is a great candidate species for the early vegetation restoration in the dry-hot valley region. This work provides a reference for vegetation restoration and rational utilization of soil resources in degraded ecosystems in dry-hot valleys and other soil erosion areas.

Effects of Vetiveria zizanioides on the Restoration and Succession of Coal Gangue Mountain Plant Communities in Different Years

The restoration of vegetation on coal gangue mountains has always been an area of concern, and therefore, an important area of research. Liupanshui city in Guizhou province, China, has a large number of coal gangue mountains, and for this reason, was chosen for studying vegetation succession on these sites. Vetiveria zizanioides is known to accelerate the restoration of vegetation on coal gangue mountains and to shorten community succession timeframes. Because of this, we investigated different successional stages after the planting of V. zizanioides on coal gangue mountains in the Dahe coal mine comprehensive environmental governance project area in Liupanshui city. Through field community surveys and model prediction, the effects of planted V. zizanioides on the species composition, species diversity, and community succession of gangue mountains 3, 6, 8, 10, and 13 years after planting were explored. In total, 35 plant species belonging to 17 families and 32 genera were recorded across the five different coal gangue mountains. With more time after planting, the height, coverage, density, and biomass of V. zizanioides all decreased, but increased for Miscanthus floridulus. The Simpson diversity index, Shannon–Wiener diversity index, and Pielou evenness index all first increased before decreasing over time; maximum values were recorded for the coal gangue mountain 8 years after planting of V. zizanioides. According to different similarity and dissimilarity indices, the successional stages became more similar with increasing time after planting. According to biomass fitting and prediction curves, the succession process of coal gangue mountain plant communities could be divided into a V. zizanioides community stage, a M. floridulus community stage, and a woody plant stage, that starts to approach the natural community of evergreen broad-leaved forests, with durations of 0–5.62 years, 5.62–17.48 years, and over 17.48 years, respectively.

Comparison of the Vegetation Index of Reclamation Mining Areas Calculated by Multi-Source Remote Sensing Data

Following vegetation reclamation in mining areas, secondary damage may occur at any time, especially in locations that have been mined for decades or even hundreds of years. Effective monitoring strategies are required to accurately assess plant growth and to detect the ecological effects of reclamation. Single satellite monitoring is often difficult to ensure vegetation monitoring needs, therefore multi-source remote sensing is preferred. Different sensor parameters and variation in spectral bands can lead to differences in the type of data obtained, and subsequently, methods for evaluating these differences are required for simultaneous sensor/band use. In this study, NDVI was selected to characterize the vegetation growth of the Antaibao Open-pit Coal Mine Dump by analyzing the correlation between different types of sensors (Landsat 8, HJ, Sentinel-2) and vegetation greenness in order to facilitate satellites’ replacement and supplement. Results show that: (1) Landsat 8 and Sentinel-2 satellite have a high relevance for monitoring the vegetation, but the correlation between these two sensors and HJ is relatively low, (2) the correlation between NDVI values varied by vegetation type, tree (R = 0.8698) > combined grass, shrub and tree (R = 0.7788) > grass (R = 0.7619) > shrub (R = 0.7282), and (3) the phenomenon of “Low value is high, high value is low” in the NDVI value with HJ satellite monitoring may have been caused by a weak signal strength and low sensitivity of the HJ sensor. Comparing the correlation of multi-source sensors to monitor the vegetation in the mining areas can be helpful to determine the alternative supplement of sensors through conversion formulas, which are helpful in realizing the long-term monitoring of dumps and detecting reclamation response in mining areas.

Optimization of Reclamation Measures in a Mining Area by Analysis of Variations in Soil Nutrient Grades under Different Types of Land Usage—A Case Study of Pingshuo Coal Mine, China

The development of reclaimed mine soils is normally spatially heterogeneous, making the fine management and utilization of reclaimed mined lands difficult. Soil nutrient grading can provide a scientific basis for the precise regulation of soil nutrients, but few related studies are available in reclaimed mined areas. This study aimed to quantify the spatiotemporal variations in soil nutrient grades under different land-use types in a reclaimed mined area on the Loess Plateau, China. The study area was graded by four soil nutrients (soil available potassium (SAK), soil available phosphorus (SAP), soil total nitrogen (STN), and soil organic matter (SOM)), and the variation features of soil nutrient grades in the initial stage of reclamation under four land-use types (i.e., cultivated land, grassland, forestland, and barren land) were systematically characterized by geostatistical analysis, pedodiversity analysis, and correspondence analysis. The results show that during the initial five years after reclamation, the soil nutrient grades of most reclaimed areas increased from Grade V and VI to Grade I–IV, while the improvements were significantly heterogeneous. Notably, the four land-use types had distinct variation characteristics. The barren land had the lowest SAP level, whereas it had the highest proportion, and medium–high grades of SAK, STN, and SOM (88.3, 100.0, and 100.0%, respectively). In terms of quantitative structure, it had the lowest richness index (S′, 2.5) and Shannon’s entropy index (H′, 0.7) and the highest evenness index (E′, 0.8). These results suggest that the barren land had relatively high and balanced nutrients, with the highest homogeneity among the four land-use types. The grassland had considerable improvement in all nutrients (especially SAP; 95.6% of the area had high SAP grades); however, its improvement was the most heterogeneous (S′ = 4.5, E′ = 0.7). As the second-most heterogeneous land-use type (S′ = 4.0, E′ = 0.8), the forestland had relatively low STN, SAP, and SAK levels due to high nutrient uptake and storage by tree species, but it had the highest proportion of area that reached high SOM grades (36.4%) and medium to high SOM grades (100.0%) due to its high community productivity. The cultivated land, which received fertilization for an additional three years, was the most imbalanced in terms of nutrients. It had the highest proportion of area that reached high SAP grades (98.0%); in contrast, its area proportions of low-grade SAK and SOM (69.0 and 32.9%, respectively) were the highest among the four land-use types. Based on the above comprehensive characterization of soil nutrient grade variation, guidance was given for fine management of reclaimed mined land and the optimization of reclamation measures.