Abstract
Coal gangue piles accumulate outside mines and can persist for years, negatively impacting the regional environment. To determine the main cause of soil pollution at coal gangues, several coal gangues in Guizhou Province, China that had undergone natural recovery via native plants for 8 years were investigated in summer 2019. Three plots (2 m × 2 m) from the coal gangue area were selected for the treatment (GP). Control plots that were 100 m away from GP were also investigated in contrast (CK-near). In addition, plots from forest, farmland and lake land that were far from GP and largely undisturbed were also investigated as more extreme contrasts (CK-far). A series of soil indicators that can be affected by coal-gangue, such as heavy metals (Mn, Cr, Cd, Ni, Zn, Cu, Pb), As, pH, cation exchange capacity (CEC), sulfur (S) and iron (Fe), were tested for in the plots. Plant species, coverage and height were also analyzed to uncover biodiversity and dominant species information. The results suggested that coal gangue significantly influences soil S, pH and plant species after 8 years of natural recovery. The CK-far plots contained relatively low soil sulfur content, normal pH (close to 7) and abundant plant biodiversity. Generally, pH related positively with both the Patrick (R = 0.79, n = 22, p < 0.001) and Shannon indices (R = 0.67, n = 22, p < 0.001); the soil S related negatively with both the Patrick (R = 0.85, n = 22, p < 0.001) and Shannon indices (R = − 0.79, n = 22, p < 0.001). S content was highest (S = 1.0%) in GP plots, was lower in CK-near plots (S = 0.3%) and was the lowest of all in the plots distant from the coal mine (S = 0.1%, CK-far). S content was negatively correlated with pH. Soil pH decreased significantly, from 7.0 in CK-far, to 5.9 in CK-near, to 4.2 in GP. Soil Fe was 3.4 times higher in GP and CK-near than in CK-far. The excess sulfur and Fe elements and the acidified soil drove changes in soil and vegetation in the coal gangue areas. After 8 years of natural recovery, only a few plants, like Miscanthus floridulus, were able to live near the coal gangue in the area where the soil was still acidic and high in S and Fe.
Highlights
Coal mining is indispensable due to the widespread use of coal, and gangue is the accumulated solid waste byproduct that persists in mined lands, even after the mines have been abandoned[1]
Environmental health[13,14,15], and heavy metals are quite common in the soil around coal gangue dumps[3,16,17]
Ao and Huang’s research (2005)[18] conducted in the Wuda mining gangue dump of Inner Mongolia found that the environment had been heavily polluted by the low soil pH value and the high concentration of S O42– in the surface water around the gangue dump
Summary
Coal mining is indispensable due to the widespread use of coal, and gangue is the accumulated solid waste byproduct that persists in mined lands, even after the mines have been abandoned[1]. When exposed to atmospheric oxygen conditions, waste water that leaches from coal gangue may produce acidic drainage. This is due to the oxidation of sulfide minerals, which is associated with a variety of toxic heavy metal elements. At a large number of abandoned coal mining areas, coal mining waste and discharge pollutes the surrounding soil and water, thereby affecting agricultural land and even human populations. Near the entrances and within a small radius of these abandoned mines, some gangues are still piled up These coal gangue dumps can be paired with the undisturbed lands nearby to compare and study how residual coal gangue dumps affect the surrounding soil and plants. Soil contains a mass of chemical information, and plants are sensitive indicators of the environment, so studying these two elements offers a fairly holistic picture
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