This paper investigated the application of an improved perfusion method for microbial-induced calcium carbonate precipitation（MICP）technology in the solidification of heavy metals. Bacillus pasteurii was employed as the urease-engineered bacterium, and a 0.5cm diameter channel filled with pebbles and wire mesh was constructed to facilitate the injection treatment of industrial solid waste tailings. The migration behavior of heavy metals in the tailings was examined, the mechanisms of MICP solidification were analyzed, and a risk assessment was conducted. The results indicated that, following MICP treatment, the migration factors（MF）of Cu, Pb, and Cd in the tailings were significantly reduced by 78.94%, 61.88%, and 64.06%, respectively. Calcium carbonate precipitation was formed, filling the tailings model box and significantly increasing the residual fractions of Cu, Pb, and Cd（76.43%~92.48%）. Consequently, the environmental risks of Cu, Pb, and Cd were reduced from very high to moderate levels, significantly lowering the pollution risk of the tailings. The improved perfusion method was shown to enhance the diffusion channels of the bacterial solution, increased its contact efficiency with the tailings, promoted rapid calcium carbonate precipitation and solidification, and ensured uniform penetration while avoiding uneven solidification. This study provides a valuable reference for the engineering application of MICP technology in heavy metal pollution remediation.

A 120-day soil incubation experiment was conducted to investigate the effects of rice husk biochar on soil properties and cadmium（Cd）immobilization in polypropylene micro-/macroplastics and Cd co-contaminated soils. The results showed that biochar addition significantly improved soil pH in the co-contaminated soils compared to the control group. It also considerably increased the content of dissolved organic carbon in soils co-contaminated by 7% plastics and Cd. In addition, biochar promoted the conversion of Cd from the active form into relatively stable form in the particulate organic matter and mineral fractions, effectively reducing both the bioavailable Cd content and the proportion of DTPA-extractable Cd（DTPA-Cd）in the co-contaminated soils. Specifically, biochar reduced the bioavailable Cd content by 7.58%~19.71% and the DTPA-Cd proportion by 20.23%~30.83% in microplastics and Cd co-contaminated soils. For macroplastics and Cd co-contaminated soils, the corresponding reductions were 23.80%~28.19%and 21.63%~22.74%, respectively. Notably, the concentration of microplastics was positively correlated with the content of bioavailable Cd, while the concentration of macroplastics showed no significant effect on it. The findings demonstrated that rice husk biochar effectively alleviated the adverse effects of the plastics and Cd co-contamination through improving soil properties, mediating the migration and transformation of Cd among soil solid fractions, as well as adsorbing and immobilizing Cd.

In this study, we conducted a laboratory experiment to study the effects of oxygen-loaded biochar on nitrogen transformation and arsenic migration in paddy soil, and to assess the inhibition effect of oxygen-loaded biochar on arsenic migration in paddy soil-rice system. The results showed that the oxygen-loaded walnut shell biochar reduced the pH of pore water, alleviated the decline of DO and increased Eh. Meanwhile, the abundance of amoA gene in the paddy soil significantly increased（P<0.05）, which promoted the nitrification process. Also the the release of nitrous oxide was reduced and the loss of total nitrogen was depressed. After 80days, the arsenic（III）content in the paddy soil in the oxygen-loaded biochar and biochar applied treatment accounted for 42.6%、51.9%, respectively, which were significantly lower（P<0.05）than that in control（90.2%）. The amendment of oxygen-loaded biochar was also responsible for the increase in the height and tillers of rice, as well as the accumulation of iron plaque around rice root, which reached 18.4 mg/kg and was 4.2 times higher than that in control. Therefore, the arsenic content in rice was reduced by 46.3%. This indicates that the addition of oxygen-loaded biochar in paddy soil increased the concentration of iron plaque in rice roots, led to more arsenic fixation, and triggered the reduction in the accumulation of arsenic in rice. The results offer a new sight to inhibit the nitrogen loss in paddy soil and arsenic mitigation in rice.

The collaborative ecological governance demonstration test project in the coal gangue backfills subsidence area of a city in Shaanxi Province provided an example for this study. This research investigated the environmental pollution risks in the backfill area, where coal gangue was used as the backfill material. It analyzed the spatiotemporal laws of heavy metal leaching and migration. The variation and processes of heavy metals in the soil were simulated using Hydrus-1D.A comparison of measured values from the soil column experiment with the simulated values verified the model, and the analysis identified relationships between infiltration distances at different periods and concentration equilibrium times in various soil layers. The results demonstrated that the established model effectively simulated the migration and change patterns of heavy metals in the soil of the backfill area. Over time, the leaching concentrations of heavy metals varied with depth, ranked as Cr（Ⅵ）= Pb>Ni>Hg, with maximum migration distances of 21.60, 21.60, 20.70 and 16.20m, respectively. At different soil layer depths, the leaching concentrations of heavy metals followed the order Pb>Cr（Ⅵ）>Ni>Hg. The concentration trends increased rapidly and stabilized, with none exceeding the limit values. The findings confirmed no significant environmental pollution impacts occurred in the coal gangue backfill subsidence area.

In this paper, we reviewed the measured data of heavy metals in farmland soils in Guangdong Province since 2010. We applied a meta-analysis approach to combine the data based on “average concentration” “number of sampling points” and “standard deviation”. The results showed that the concentration of lead（Pb, 48.83mg/kg）and mercury（Hg, 0.18mg/kg）in Guangdong Province are among the highest in China, likely influenced by industrial and mining activities. In addition, subgroup analyses explored the effects of spatial distribution and cropping systems across different cities. The results revealed that heavy metal concentrations were higher in the economically developed Pearl River Delta and mineral-rich regions. Notably, some of the most polluted cities include Foshan city（As:18.32mg/kg, Cr:73.5mg/kg, Ni: 35.4mg/kg）, Shaoguan city（Pb: 86.61mg/kg）, Shenzhen city（Cd: 0.51mg/kg）, Meizhou city（Cu: 61.1mg/kg）, etc. Among them, farmland soil Cd concentration was significantly correlated with regional industrial output value（r=0.77, P<0.01）, with additional impacts from factors such as the local population and energy consumption. The analyses of different farming systems showed that Cd, Pb, Zn, Cr, and Hg concentrations in soils were higher in land and paddy fields; while Cu, Zn, As, and Ni were enriched in orchards and facility-based agriculture, which may be related to the soil physicochemical properties, fertiliser and the geological backgrounds in different farming systems. This study provides province-wide information on the spatial distribution of heavy metals in agricultural soils and cropping systems, which is of great significance to the management and control strategies of heavy metal pollution in agricultural soils in Guangdong Province.

Taking a typical mining area as an example, statistical methods and Positive Matrix Factorization（PMF）were integrated to qualitatively and quantitatively identify key regional pollution sources and their contributors. A spatial model was further constructed, considering the spatial heterogeneity of soil heavy metal pollution and its dominant environmental drivers, with the best environmental variables and spatial scale being selected. The results revealed that the sources of soil heavy metal pollution were natural sources, exhaust gas emission sources, slag emission sources, wastewater emission sources, and transportation sources, with contributions of 8.40%, 9.55%, 1.73%, 55.37%, and 24.99% of the total pollution, respectively. Notably, atmospheric deposition（q =0.113）and soil leaching（q=0.097）were identified as the primary input and output pathways for heavy metals. Among various spatial modeling strategies, the model that integrated both spatial pollution source characteristics and environmental variables demonstrated the highest predictive accuracy, outperforming the model based solely on dominant environmental factors or pollution source characteristics. The importance of incorporating spatial information to enhance model performance was highlighted by this finding. In particular, the Geographically Weighted Regression Kriging（GWRK）model was found to achieve superior predictive accuracy（mRadius=0.2916）when multiple data sources were integrated. Overall, a scientific foundation was provided for identifying high-risk soil pollution zones in mining regions, the understanding of ecological and environmental interactions between influencing factors and heavy metal contamination was enhanced, and valuable insights were offered for spatially targeted pollution control strategies.

In this study, two paddy soils with similar organic matter contents but different iron contents were used to conduct anaerobic microcosm incubation experiments with four treatments, including Control, +NO₃^-, +As（III）, and +As（III）+NO₃^-. The transformation of arsenic, nitrogen, and iron species, as well as changes in microbial community structure and abundance were investigated in order to elucidate the effect of iron on the microbial As（III）oxidation coupling nitrate reduction processes in soils under anoxic conditions. The results revealed that As（III）oxidation was driven by nitrate reduction, and 35.3% and 43.0% of As（III）were oxidized in the soils with low iron and high iron content, respectively, at the end of incubation. The phosphate-extracted and oxalate-extracted arsenic contents were significantly higher in the soil with high iron content than those in the soil with low iron content. The presence of As（III）slowed down the nitrate reduction process, reduced the accumulation of NO₂^- and N₂O, and promoted the NH₄⁺ production. In addition, the denitrification and dissimilatory nitrate reduction to ammonium（DNRA）processes were faster in the soil with high iron content than those in the soil with low iron content. The presence of nitrate and As（III）decreased the concentrations of dissolved Fe（II）and adsorbed Fe（II）in soils, increased the concentrations of adsorbed total iron, and altered the composition and abundance of soil microbial community. Bacillus, Clostridium, and Planococcaceae were identified as the dominant bacteria during nitrate reduction and As（III）oxidation processes. This study demonstrates that soils with high content of adsorbed iron can facilitate anaerobic As（III）oxidation coupling denitrification/DNRA and enhance the immobilization of As（III）and As（V）by iron（oxyhydr）oxides in soils. These findings provide scientific basis for the regulation of arsenic transformation by iron and nitrogen elements in flooded paddy fields.

To unveil the carbon release capacity of humic soil and its potential applications in wastewater treatment, this study explored the impact of various aeration gradients on the release of dissolved organic matter（DOM）from humic soil. By establishing gradients of no aeration, low aeration, medium aeration, and high aeration, the carbon release experiment lasting 600 hours was conducted. The carbon release capacity at various time points and DOM changes in components were monitored with the aid of total organic carbon（TOC）analysis, three-dimensional fluorescence spectroscopy-parallel factor analysis（EEM-PARAFAC）, and UV-visible absorption spectroscopy. Results showed that aeration intensity significantly affected the amount and cycle of carbon release from humic soil. Before reaching medium aeration, the carbon release capacity increased with the intensity of aeration, followed by a decrease afterwards. Aeration was found to enhance the release of aromatic protein-like substance I（C1）and humic-like substances（C3）. However, the intensity and effectiveness of the enhancement varied between these two components. Conversely, aeration suppressed the release of aromatic protein-like substance II（C2）and soluble microbial metabolic substances（C4）, where differences were also observed. UV-visible absorption analysis indicated that the aromaticity and humification degree of DOM increased over time during the carbon release process from humic soil. The carbon release cycle was about 248h during the 600-h test, higher aeration intensities were found to improve the microbial utilization of DOM.

A year-long study was conducted in Taihu Lake with the objective of investigate the diffusive fluxes of methane（CH₄）across the sediment-water interface in different ecological zones, namely the algal bloom zone, the macrophyte zone, and the open water zone. The CH₄ concentrations in the sediment porewaters and the relevant fluxes at the sediment-water interface from different ecological zones of the lake were analyzed and evaluated. Results showed that CH₄ concentrations in porewaters increased with the sediment depth. The CH₄ concentrations in the open water zone were found significantly lower than that in the other zones. The organic carbon was identified as the key factor driving the spatial and temporal variations of CH₄. The mean diffusive fluxes of CH₄ across the sediment-water interface were 122.56±32.2, 108.75±23.8, and 3.36±0.6 µmol/（m²·d）in the algal bloom zone, the macrophyte zone, and the open water zone, respectively, with the open water zone showing the significantly lower fluxes. Seasonal variations of CH₄ fluxes were observed in the lake while the fluxes were significantly higher in the spring and the summer than the other two seasons. The regression result showed that the CH₄ flux was strongly influenced by the CH₄ concentration in the porewater and the sediment porosity. Our study also demonstrated that algal blooms and macrophyte reproductions enhanced CH₄ concentrations in porewaters and significantly increased the diffusive CH₄ fluxes across the sediment-water interface in Lake Taihu.

The hydro-chemical characteristics and trophic status of reservoirs are shaped by a combination of natural conditions and anthropogenic effects within the watershed. This study focuses on Xiaowan Reservoir（XW）and Danjiangkou Reservoir（DJK）to analyzes the main ions characteristics and spatial variations of nitrogen（N）and phosphorus（P）nutrients in their water bodies, we identify the primary sources of these ions and interprets the nutrient status of these karst reservoirs, along with the influencing factors. The results show that: The water chemistry of the karst reservoirs is governed by rock weathering, resulting in HCO₃·SO₄-Ca and HCO₃-Ca types for XW and DJK respectively; Both reservoirs exhibit high anthropogenic inputs of SO₄^2-and NO₃^-; In both reservoirs, nitrogen（N）and phosphorus（P）predominant exist in dissolved forms. While no carbon-limitation was observed,N-limitation is evident in XW and P-limitation in DJK, leading to a mesotrophic status in both reservoirs; The stoichiometric ratio of carbon（C）, nitrogen（N）, and phosphorus（P）are the primary factors influencing the comprehensive trophic level index（TLI）of the reservoirs. This is attributed to the karst hydrochemical background and high weathering rates; Under different N and P limiting conditions, the trophic status is affected by various factors, with the C to P ratio-sensitive to rock weathering, climate change, and anthropogenic inputs-emerging as a key determinant of water quality; To optimize the evaluation indices for assessing the trophic state and managing water quality in karst reservoirs under diverse hydrological conditions and functional roles, it is essential to analyze the effects of water chemical characteristics and stoichiometric ratios of biogenic elements on trophic status based on the analysis of nutrient limitations in water bodies.