Insights into the spatiotemporal differences in tailings seepage pollution by assessing the diversity and metabolic functions of the soil microbial community

Fungal community determines soil multifunctionality during vegetation restoration in metallic tailing reservoir

Microorganisms are pivotal in sustaining soil functions, yet the specific contributions of bacterial and fungal succession on the functions during vegetation restoration in metallic tailing reservoirs remains elusive. Here, we explored bacterial and fungal succession and their impacts on soil multifunctionality along a ∼50-year vegetation restoration chronosequence in China's largest vanadium titano-magnetite tailing reservoir. We found a significant increase in soil multifunctionality, an index comprising factors pertinent to soil fertility and microbially mediated nutrient cycling, along the chronosequence. Despite increasing heavy metal levels, both bacterial and fungal communities exhibited significant increase in richness and network complexity over time. However, fungi demonstrated a slower succession rate and more consistent composition than bacteria, indicating their relatively higher resilience to environmental changes. Soil multifunctionality was intimately linked to bacterial and fungal richness or complexity. Nevertheless, when scrutinizing both richness and complexity concurrently, the correlations disappeared for bacteria but remained robust for fungi. This persistence reveals the critical role of the fungal community resilience in sustaining soil multifunctionality, particularly through their stable interactions with powerful core taxa. Our findings highlight the importance of fungal succession in enhancing soil multifunctionality during vegetation restoration in metallic tailing reservoirs, and manipulating fungal community may expedite ecological recovery of areas polluted with heavy metals.

Pollution control performance of solidified nickel-cobalt tailings on site: Bioavailability of heavy metals and microbial response

There has been increasing attention given to nickel-cobalt tailings (NCT), which pose a risk of heavy metal pollution in the field. In this study, on site tests and sampling analysis were conducted to assess the physical and chemical characteristics, heavy metal toxicity, and microbial diversity of the original NCT, solidified NCT, and the surrounding soil. The research results show that the potential heavy metal pollution species in NCT are mainly Ni, Co, Mn, and Cu. Simultaneous solidification and passivation of heavy metals in NCT were achieved, resulting in a reduction in biological toxicity and a fivefold increase in seed germination rate. The compressive strength of the original tailings was increased by 20 times after solidification. The microbial diversity test showed that the abundance of microbial community in the original NCT was low and the population was monotonous. This study demonstrates, for the first time, that the use of NCT for solidification in ponds can effectively solidification of heavy metals, reduce biological toxicity, and promote microorganism diversity in mining areas (tended to the microbial ecosystem in the surrounding soil). Indeed, this study provides a new perspective for the environmental remediation of metal tailings.

The adaptability, distribution, ecological function and restoration application of biological soil crusts on metal tailings: A critical review

A large amount of metal tailings causes many environmental issues. Thus, the techniques for their ecological restoration have garnered extensive attention. However, they are still in the exploratory stage. Biological soil crusts (BSCs) are a coherent layer comprising photoautotrophic organisms, heterotrophic organisms and soil particles. They are crucial in global terrestrial ecosystems and play an equal importance in metal tailings. We summarized the existing knowledge on BSCs growing on metal tailings. The main photosynthetic organisms (cyanobacteria, eukaryotic algae, lichens, and mosses) of BSCs exhibit a high heavy metal(loid) (HM) tolerance. BSCs also have a strong adaptability to other adverse conditions in tailings, such as poor structure, acidification, and infertility. The literature about tailing BSCs has been rapidly increasing, particularly after 2022. The extensive literature confirms that the BSCs distributed on metal tailings, including all major types of metal tailings in different climatic regisions, are common. BSCs perform various ecological functions in tailings, including HM stress reduction, soil structure improvement, soil nutrient increase, biogeochemical cycle enhancement, and microbial community restoration. They interact and accelerate revegetation of tailings (at least in the temperate zone) and soil formation. Restoring tailings by accelerating/inducing BSC formation (e.g., resource augmentation and inoculation) has also attracted attention and achieved small-scale on-site application. However, some knowledge gaps still exist. The potential areas for further research include the relation between BSCs and HMs, large-scale quantification of tailing BSCs, application of emerging biological techniques, controlled laboratory experiments, and other restoration applications.

Habitat-specific environmental factors regulate the spatial variability of biological soil crust microbial communities on the Qinghai-Tibet Plateau

Biological soil crusts (BSCs) are an important biological component of the soil surface, covering approximately 12 % of the Earth's land surface. Although BSCs are closely related to habitats, the microbial diversity and spatial variability of BSCs in different ecosystems are still unclear, especially on the Qinghai-Tibet Plateau (QTP), where climate is changeable and habitats are complex. Here, we investigated the diversity, assembly processes, spatial distribution pattern and driving factors of prokaryotic and eukaryotic microbial communities in BSCs in four habitats on the QTP. It was found that habitat-specific environmental factors regulated the composition, diversity and spatial variability of BSC microbial communities. Soil organic carbon and soil water content were the most important factors (R2 = 0.9024, P = 0.001; R2 = 0.8004, P = 0.001) affecting the spatial differences in prokaryotes and eukaryotes, respectively. Under the specific climate of the QTP, the spatial pattern of microbial communities in BSCs was controlled by precipitation rather than temperature. In addition, ecological processes further explained the effects of habitat specificity, and environmental filtering explained microbial community differences better than dispersal limitation. The results of the neutral community model and the normalized stochastic ratio index revealed that the assembly of prokaryotic communities was determined by deterministic processes at the regional scale, and at the local scale, the assembly process was mainly determined by habitat type, while the assembly of eukaryotic communities was determined by stochastic processes at both the regional and local scales. This study provided a scientific reference for the prediction of BSC distribution and resource conservation under future climate change scenarios.

Mechanism of downward migration of quinolone antibiotics in antibiotics polluted natural soil replenishment water and its effect on soil microorganisms

Reclaimed water is widely concerned as an effective recharge of groundwater and surface water, but trace organic pollutants produced by traditional wastewater treatment plants (WWTPs) would cause environmental pollution (water and soil) during infiltration. Therefore, the effects of reclaimed water containing ofloxacin (OFL) and ciprofloxacin (CIP) in antibiotics polluted natural soil (APNS) were investigated by simulating soil aquifer treatment systems (SATs). The experiment results showed that OFL and CIP in water were adsorbed and microbially degraded mainly at 30 cm, and the concentration of OFL and CIP in soil increased with depth, which were mainly due to the desorption from APNS. Concurrently, the change in replenishment water concentration also significantly affected OFL and CIP in pore water and soil. Although OFL and CIP inhibited the diversity of soil microbial community, they also promoted the growth of some microorganisms. As the dominant bacteria, Proteobacteria and Acidobacteriota can effectively participate in the degradation of OFL and CIP. The degradation effects of soil microorganisms on OFL and CIP were 45.48% and 42.39%, respectively, indicating that soil microorganisms selectively degraded pollutants. This experiment was carried out on APNS, which provided a reference for future studies on the migration of trace organic pollutants under natural conditions.

Insights into remediation effects and bacterial diversity of different remediation measures in rare earth mine soil with SO4 2- and heavy metals

The increased demand for rare earth resources has led to an increase in the development of rare earth mines (REMs). However, the production of high-concentration leaching agents (SO₄ ^2-) and heavy metals as a result of rare earth mining has increased, necessitating the removal of contaminants. Here, a series of experiments with different remediation measures, including control (CK), sulfate-reducing bacteria (SRB) alone (M), chemicals (Ca(OH)₂, 1.5 g/kg) plus SRB (CM-L), chemicals (Ca(OH)₂, 3.0 g/kg) plus SRB (CM-M), and chemicals (Ca(OH)₂, 4.5 g/kg) plus SRB (CM-H), were conducted to investigate the removal effect of SO₄ ^2-, Pb, Zn, and Mn from the REM soil. Then, a high-throughput sequencing technology was applied to explore the response of bacterial community diversity and functions with different remediation measures. The results indicated that CM-M treatment had a more efficient removal effect for SO₄ ^2-, Pb, Zn, and Mn than the others, up to 94.6, 88.3, 98.7, and 91%, respectively. Soil bacterial abundance and diversity were significantly affected by treatments with the inoculation of SRB in comparison with CK. The relative abundance of Desulfobacterota with the ability to transform SO₄ ^2- into S^2- increased significantly in all treatments, except for CK. There was a strong correlation between environmental factors (pH, Eh, SO₄ ^2-, Pb, and Zn) and bacterial community structure. Furthermore, functional prediction analysis revealed that the SRB inoculation treatments significantly increased the abundance of sulfate respiration, sulfite respiration, and nitrogen fixation, while decreasing the abundance of manganese oxidation, dark hydrogen oxidation, and denitrification. This provides good evidence for us to understand the difference in removal efficiency, bacterial community structure, and function by different remediation measures that help select a more efficient and sustainable method to remediate contaminants in the REM soil.

Characteristic pollutants and microbial community in underlying soils for evaluating landfill leakage

Leachate leakage poses a serious environmental risk to the safety of surrounding soils and groundwater. A much faster approach to reflect landfill leakage is the premise to mitigate the ecological risk of landfills. In this study, two landfills (BJ and WZ) were selected to investigate the leaching characteristics of various pollutants along the vadose soil depths. The physiochemical properties of underlying soils including NO₃^--N, NO₂^--N, NH₄⁺-N, OM, TN, EC and Cl^- exhibited a typical leaching dynamic along the depths. Among them, TN, NH₄⁺-N, OM, NO₃^--N, and EC might be used as characteristic pollutants to evaluate the leachate leakage issues in landfilled sites. The genera Thiopseudomonas, Acinetobacter, Pseudomonas, and Hydrogenispora dominated in underlying soils. Compared to BJ samples, a more diverse and active microbiome capable of carbon and nitrogen cycles was observed in WZ samples, which was mainly ascribed to nutrients and elements contained in different types of soils. Among the environmental factors, nitrogenous compounds, SO₄^2-, pH and EC had significant effects on the microbial community structures in the underlying soils. The relative abundances of Hydrogenispora and Caldicoprobacter might be used as characteristic microorganisms to evaluate the leachate leakage issues in landfilled sites. These results provided a deep insight into effects of leachate leakage in underlying soils, especially the pollutants vertical distribution and the corresponding microbial community structures.

Gradient rise in seepage pollution levels in tailings ponds shapes closer linkages between phytoplankton and bacteria

A large number of tailings ponds formed by slag accumulation have become serious environmental hazards. Spatially high potential energy and long-term accumulation may result in gradient-changing seepage pollution. The assemblages of phytoplankton and bacteria are widely used as assessment indicators. In this study, we investigate the changes in phytoplankton and bacterial assemblages in tailing pollution. The results showed that there are temporal and spatial variabilities in seepage pollution. The abundance and diversity of phytoplankton and bacteria decreased with increasing pollution. However, Synedra acus (diatom) and Polynucleobacter (bacteria) were positively correlated with pollution levels (r = 0.37, P < 0.05; r = 0.24, P < 0.05). Heavy metals are the main contributors to bacterial changes (16.46%), while nutrients are for algae (13.24%). Tailings pond pollution reduced the number of phytoplankton and bacterial linkages. However, more pollution broke the originally independent modules of phytoplankton and bacteria, and they produced more positive correlations (79.39%; 87.68%). Microcystis sp. and Limnobacter were the key nodes of the co-occurrence network in the polluted areas. Exploring the interactions between bacteria and phytoplankton within different pollution levels could provide insights into biological interaction patterns and the bioremediation of tailings ponds.