Potential and Mechanisms for Stable C Storage in the Post-Mining Soils under Long-Term Study in Mitigation of Climate Change

Carbon storage in soil increases along with remediation of post-mining soils. Despite many studies on the issue of carbon sequestration in soils, there is a knowledge gap in the potential and mechanisms of C sequestration in post-mining areas. This research, including nuclear magnetic resonance analysis, determines the soil organic carbon formation progress in a long-term study of limestone (S1), and lignite (S2) post-mining soil under different remediation stages. The main remediation target is reforesting; however, S2 was previously amended with sewage sludge. The study showed that for S1, the O-alkyl groups were the dominant fraction in sequestered soil. However, for S2, increased fractions of acetyl-C and aromatic C groups within remediation progress were observed. The remediation of S1 resulted in improved hydrophobicity and humification; however, the decrease in aromatic groups’ formation and C/N ratio was noted. For S2, we noticed an increase for all indicators for sequestered C stability, which has been assigned to the used sewage sludge in remediation techniques. While both post-mining soils showed huge potential for C sequestration, S2 showed much higher properties of sequestered C indicating its higher stabilization which can suggest that soils non-amended with sewage sludge (S1) require more time for stable storage of C.

New Approach for Mining Site Reclamation Using Alternative Substrate Based on Phosphate Industry By-Product and Sludge Mixture

Mining soils are generally characterized by soils having a coarse texture and low fertility, which makes revegetation a very difficult and delicate operation, especially in arid and semi-arid zones. The main objective of this work is to evaluate different substrates that can both contribute to the successful reclamation of phosphate mining soils and the valorization of phosphate by-product and sewage sludge. The study was carried out in pots under a greenhouse on Italian ryegrass (Lolium multiflorum). The experimental design is a randomized complete block with ten treatments, four repetitions from five substrates: phosphogypsum (PG), phosphate sludge (PS), sewage sludge (SS), topsoil from mining (TS) and phosphate waste rocks (PWR); this corresponds to soil after rock phosphate extraction. Nitrogen fertilization was applied to treatments after soil depletion in treatments not receiving sludge. An aerial biomass measurement and nutrient analysis were carried out for the three cuts. The results showed that a proportion of 65% of PG enriched the substrate in phosphorus by improving the crop yield. The addition of 5% of SS contributed to a significant improvement of ryegrass aerial biomass. In the absence of SS application, the addition of nitrogen is required to maintain crop growth. For large-scale application, TS can be mixed with PS, SS and PG for mine site reclamation.

The Influence of Compost Amendments on Bioaccumulation of Potentially Toxic Elements by Pea Plant Cultivated in Mine Degraded Soils

Potential toxic metals (PTEs) accumulation in soil and water is one of the major sources of food crop contamination. PTEs remediation from soil can be enhanced by addition of organic matter to the growing media. An experiment was carried out to investigate the effect of different organic amendments on the accumulation of PTEs in pea plant grown on mine degraded soils. Mining soils from chromite mine (CM), soap stone mine (SSM), manganese mine (MM) and quartz mine (QM) were mixed with vermicompost (VC), leaf mould (LC) and spent mushroom compost (SMC) along with garden soil at 1:1:1 ratio. Various growth and yield related attributes of pea plant as well as PTEs concentrations in soil and plants were studied. The highest Cd (2.62 mg kg−1) and Cr (13.6 mg kg−1) concentration was reported in CM soil, while Pb (23.3 mg kg−1) and Mn (59.2 mg kg−1) concentration in SSM and MM soil, respectively. Mining soils significantly reduced the plant growth and yield, while organic amendments reduced the PTEs availability and increased pea plant growth. Comparing the various organic fertilizers used, it was observed that VC efficiently reduced Cd, Cr, Pb and Mn uptake by pea plant, subsequently, improved pea plant growth. In order to assess the effects of various amendments on PTEs health risk reduction various risk indices including, plant trafser factor, average daily intake, health risk, target hazard quotient and target cancer risk were also calculated and the results revealed that application of compost particularly VC significantly reduced the dietary intake and health risks of PTEs.

Molecular Characterization of Distinct Fungal Communities in the Soil of a Rare Rarth Mining Area

The exploitation of ion absorbed rare earth elements (REEs) has caused serious ecological destruction and environmental pollution. Effect on soil fungal structure and diversity caused by mining activities are usually ignored, although fungi are one of the most important components in soil ecosystems. In the present research, quantitative polymerase chain reaction (qPCR) and high-throughput Illumina MiSeq sequencing were conducted to characterize fungal community composition and structure in soil of a rare earth mining area after in-situ leaching. Statistical analyses, Network and FUNGuild were used to conduct in-depth analysis. Ascomycota, Basidiomycota, Glomeromycota and unclassified fungi were the most abundant phyla in the mining soils. Organic matter, TC and TN contents, but not pH or REEs contents, were the vital factors to determine soil fungal abundances and diversities. Fungal community structures were stable after leaching practice, but nutrition contents significantly and positively contributed to fungal abundances and diversities. Fungi could mediate the interaction between species to enhance their ability to resist the harsh environment of REEs toxicity or ammonium caused by in-situ leaching practice. Saprotroph in phyla Ascomycota and Basidiomycota were the dominant fungal trophic mode in the mining soils, and they played a critical role in nutrient cycling, transformation processes and reducing metal toxicity. Symbiotrophs of phyla Glomeromycota contributed to soil aggregation and slowing down nutrient losses after in-situ leaching practice.