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Introduction: This study evaluates the effectiveness of soil reconstruction and restoration in the Jiangcang coal mining area on the Qinghai-Tibet Plateau, where harsh environmental conditions pose significant challenges to ecological restoration.

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 ( R 2 ) of each segment was higher than 0.940, and the average value of the five-segment R 2 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.

PurposeThe 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 methodsA 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 discussionCompaction generally reduced VD, SD, and MCD, which ranged from 0.10 to 0.20, 2.23 to 2.80 mm2 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 mm2 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.ConclusionsAll 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.

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 Chinese government attaches great importance to the ecological restoration of abandoned open-pit mines, increasing the area of cultivated land, and ensuring food security. Soil reconstruction is a crucial step in ecological restoration of abandoned open-pit mines. This study investigated the utilization of hydrophobic sand to create an Air-Permeable Aquiclude (APAC) under the plant root zones, thereby minimizing water infiltration and enhancing soil aeration. Field plot experiments for 2 years have been conducted, with control groups, Clay Aquitard (CAT), and Plastic Aquiclude (PAC), to evaluate the effects of APAC on rice yield, nitrogen utilization, and water efficiency. The findings revealed that utilizing APAC resulted in a significant rise in rice yield, ranging from 8.09 t/hm² to 9.27 t/hm², which were 7.67–27.16% higher than the control groups. Moreover, the APAC led to a remarkable reduction in irrigation water usage by 37.08%, alongside a substantial boost in Irrigation Water Productivity (IWP) efficiency by 28.64–71.12%. Notably, Nitrogen Partial Factor Productivity (NPFP) exhibited a substantial increase of 7.69–27.06%. These outcomes underscore the APAC’s positive role in water and nutrient conservation and enhanced yields.

Soil microbes are the main driving forces and influencing factors of biochemical reactions in the environment. Study of ecological recovery after mining activities has prompted wider recognition of the importance of microbial diversity to ecosystem recovery; however, the response of soil bacterial communities to vegetation restoration types and soil biochemical properties remains poorly understood. The purpose of this research was to explore the soil bacterial communities and soil biochemical properties at four sampling sites (brushland (BL), forestland (FL), grassland (GL) and unreclaimed land (UL)) on the Loess Plateau, China, to evaluate the effect of vegetation restoration on the reconstructed soil in mining areas. In August 2017, samples were collected at the Heidaigou coal mine dumps. Illumina MiSeq sequencing was used to identify the structure of the soil bacterial community and evaluate its relationships with soil biochemical properties. The results showed that soil biochemical properties (soil organic matter, available phosphorus, urease, sucrase, microbial biomass carbon and microbial biomass nitrogen) were significantly increased in BL, FL and GL relative to UL, indicating that the soil quality was significantly improved by vegetation restoration. In addition, the results showed that the vegetation restoration on the reconstructed soil in the mining area could significantly improve the operational taxonomic units (OTUs), abundance (ACE and Chao1) and diversity (Shannon and Simpson) indices of bacterial community and the dominant phyla were Proteobacteria, Actinobacteria and Acidobacteria. With vegetation restoration, the relative abundance of Proteobacteria and Acidobacteria showed an increasing trend, while that of Actinobacteria showed a decreasing trend, and the dominant phyla were only significantly correlated with a few biochemical properties. Moreover, there were no changes in soil bacterial community structures across the four sampling sites and the response of the bacterial community to biochemical properties was not obvious. This implies that, although the region has experienced about 20 years of vegetation restoration, the microbial community still maintains good stability and lagging response to soil biochemical properties. Since the BL soil had better biochemical properties and higher bacterial richness and diversity, it was recommended as the optimum vegetation restoration type for soil reclamation in this area.

The complex formation process of reconstructed soil triggers the high spatial variability of soil physical properties, for which traditional soil sampling methods are not applicable due to the destructive and time-consuming modes. Ground penetrating radar (GPR) can collect continuous and high-resolution data flexibly, but the technology has rarely been employed to detect reconstructed soil properties in opencast coalmine regions. This study explored the applicability and accuracy of GPR in measuring reconstructed soil bulk density (RSBD) in southern dump, expanded western dump, and internal dump of the Antaibao open-pit mine, China. The variations of RSBD and the relationships between the dielectric constant and RSBD were analyzed based on ring knife sampling weighing, GPR detection, variance analysis, and fitting analysis. The results showed that (1) RSBD exhibited significant variations in different dumps and at different depths of the same profile. (2) RSBD differences in different dumps could be qualitatively analyzed based on the large-amplitude signals in GPR images. (3) When the soil volume moisture content ranged from 15 to 25%, RSBD was found to be negatively correlated with the dielectric constant. GPR has the potential to be widely employed to detect RSBD in reclaimed lands, which can contribute to the development of non-destructive quality testing of land reclamation.

A large number of loose piles formed by mountain hazards are highly susceptible to hydraulic erosion under rainfall conditions. The use of ecological substrate materials for erosion control and ecological restoration of gravel soil slopes has become a current research hotspot and the study difficulty. The post-earthquake slump accumulation gravel soil in Jiuzhaigou was selected as the research object, and the self-developed modified glutinous rice-based material was used to reinforce the gravel soil. The variable slope flume erosion test and rainfall simulation test were carried out to study the water erosion resistance of the material reconstructed soil under the influence of runoff erosion and raindrop splash erosion. The results show that: As the material content reached 12.5%, the reconstructed soil did not disintegrate after 24 hours of immersion, the internal friction angle was increased by 42.26%, and the cohesion was increased by 235.5%, which played a significant reinforcement effect. In the process of slope erosion, the soil rill erodibility parameter Kr was only 3‰ of the gravel soil control group, the critical shear force τ increased by 272%, and the soil erosion resistance was significantly improved. In the process of rainfall and rainfall on the slope, the runoff intensity of the reconstructed soil was stable, and the ability to resist runoff erosion and raindrop splash erosion was enhanced. The maximum value of soil loss rate on different slope slopes is 0.02–0.10 g·m −2s−1 , which is significantly lower than that of the control group and has better erosion reduction effect.

Soil reconstruction is at the core of mine land reclamation. Reconstructed soil from an opencast mine dump in a loess area is a complex composite that was assembled by humans, using multiple reconstruction technologies. The soil is composed of varied soil particles with irregular shapes and has self-similar structure. To better quantify the characterization of reconstructed soil in this dump, the soil particle-size distribution from four modes of soil reconstruction in the Shanxi Pingshuo Antaibao opencast coal-mine dump was analyzed using multi-fractal theory. Soil reconstruction modes included loess material containing gravel (LG), loess material containing coal gangue (CG), total loess material (AL) and loess material containing ginger stone (LGS). Soil particle composition, gravel content, field water capacity, soil bulk density, soil organic matter, total nitrogen (TN), soil pH and electrical conductivity (EC) of different soil layers from different reconstruction modes were measured. A generalized dimension spectrum D(q), multi-fractal singularity exponent α(q) and multi-fractal spectrum function f(α(q)) were calculated. Relationships between soil properties and fractal parameters were analyzed. The results led to the following conclusions: (1) the soil particle distribution of reconstructed soil had significant multi-fractal characteristics in an opencast coal-mine dump in a loess area. D(0), D(1), D(1)/D(0), Δα and Δf can reflect the non-uniform particle-size distribution characteristics. D(0), D(1)/D(0) and Δf (or D(0), D(1)/D(0) and Δα) can be simplified as three parameters to quantify the multi-fractal characterization of the reconstructed soil particle distribution. (2) After reclamation, the soil quality from different layers of different profiles in different reconstruction modes shows some improvement. (3) There were strong correlations between multi-fractal parameters and soil properties. D(1) and Δα increased and D(1)/D(0) and Δf decreased with increasing gravel content, soil bulk density, organic matter, TN and soil EC; however, it was opposite for pH and field water capacity. Gangue and gravel have a definite impact on the dispersion degree of soil particles in reconstruction. This study provides a theoretical basis for land reclamation and quantitative expression of reconstructed soil particles’ distribution in opencast coal-mine dumps in loess areas.

Ecological restoration techniques are extensively employed in the ecological restoration of damaged mountain ecosystems via effectively restoring the plant community and improving soil functions. Aggregate spray seeding technology as an effective ecological restoration method, can quickly restore the damaged slopes to their previous status and keep the ecosystem functions. However, the lack of understanding of the characteristic of carbon storage as well as its influencing factors limits the scientific management of carbon sink function of the rehabilitated damaged mountain ecosystem. In this study, relying on field surveys in the East Ussuri River Basin, we analyzed the carbon storage distribution and its influencing factors in damaged mountain slopes that had been restored through the spray seeding technology after an 8-year restoration phase. The results showed that the carbon storage distribution of the damaged slopes repaired by aggregate spray seeding is in the order of soil layer > tree layer > shrub layer > litter layer > herbaceous layer. Among them, the carbon storage of the vegetation layer is mainly distributed in the tree layer, and its size is similar to that of undisturbed natural slopes. Plants and soil are the main factors affecting the carbon storage of the repaired slopes, where the plant density has a significant positive correlation with carbon storage, accounting for 19% of the carbon storage variation, and the soil bulk density has a significant negative correlation with carbon storage, accounting for 23.7% of the carbon storage variation. This study reveals the mechanism of the aggregate spray seeding technology in restoring the carbon storage of damaged slopes and points out that regulating vegetation density and improving soil conditions are key to enhancing the carbon sink capacity of slopes.