There is the potential for nitrate contamination in the northern karst area. Systematically investigating the spatiotemporal pattern of surface water nitrate and the sources of pollution is extremely important for the timely recognition of the pollution hazard and the accurate location of the sources of pollution. Based on the representative watershed in the northern karst area, the Wuhushan Reservoir Basin, this study carried out evenly distributed sampling on the three main rivers of Jinyangchuan, Jinyunchuan, and Jinxiuchuan. A total of 54surface water samples from 18points along the major streams and primary tributaries were collected in the dry season, normal season, and wet season. By combining hydrochemical analysis, redundancy analysis (RDA), nitrogen and oxygen isotope methods, and the Bayesian isotope mixing model (SIAR), the study outlined the spatiotemporal pattern characteristics of nitrate in the basin's intricately interconnected surface water system and quantitatively estimated the contribution rates of different sources of pollution. The results showed that: ① The hydrochemical conditions in the research area were favorable for nitrification, with low ammonium and nitrite nitrogen contents persistently throughout the three seasons. Average nitrate contents in the dry season were greater than the normal season and wet season. Nitrate contents remained low in the upper reaches of Jinxiuchuan throughout the periods, while the downstream segments (S7-S9) had much higher nitrate contents in the dry season and normal season. Spatial differences in nitrate contents in the wet season narrowed, with relatively high contents at stations X2 and X3 in Jinyangchuan, Y2 and Y3 in Jinyunchuan. ② During the entire course of the three seasonal periods, assimilation and denitrification did not play a dominant role in the nitrate transport and transformation process, with the prevalence of nitrification. ③ During the wet season, nitrate in surface water in the study area came mainly from non-point source pollution, of which soil organic nitrogen was 62.81%. Pollution sources in the normal season were richer in composition, with soil and manure/sanitary sewerage supplying 48.85% and 21.96%, respectively. Sewage from household discharge was the major source in the dry season, which contributed to the surface water nitrate to the extent of 68.03%. These discoveries provide scientific support for the prevention of nitrate pollution and environmental protection of surface water in the northern karst area in China.

Polydimethylsiloxane (PDMS) is widely applied in daily-use products, medical treatment and power industry. In order to achieve its harmless disposal, the microbial green degradation approach was explored, and the pyrolysis characteristics, composition, production mechanism and surface hydrophobicity (CSH) of microbial cell membrane during the degradation process were analyzed. Results demonstrated that CGMCC 0452 strain exhibited strong tolerance to high-viscosity PDMS when polydimethylsiloxane (PDMS) was treated with Pseudomonas aeruginosa strain (CGMCC 0452). With the extension of degradation days, the CSH increased to 16%, and the CO stretching vibration of the carbonyl group in the chemical structure of the rhamnolipid chain was detected at 1712 cm^-1 by Fourier transform infrared spectroscopy. Gel permeation chromatography analysis revealed that the weight-average molecular weight and number-average molecular weight of PDMS decreased by 29130 Da and 21701 Da, respectively. Based on the above results, combined with comprehensive analysis of gas chromatography-mass spectrometry, it was determined that the long chain of polysiloxane was mainly degraded into cyclosiloxane oligomers (D5, D6, D8, D9), and the degradation products did not appear toxic and harmful substances. Finally, the CSH enhancement mechanism (rhamnolipid adsorption and cell membrane lipopolysaccharide loss) and cyclosiloxane oligomer formation mechanism were revealed from the micro level. This paper provides a novel research idea for the efficient and harmless treatment of polysiloxane, and offers a valuable reference for investigating the biodegradation mechanism of polymers.

This study addresses the limitations of traditional landfill groundwater pollution risk prediction methods by integrating high-performance simulation with uncertainty analysis to more accurately capture the effects of concealed leakage. The limitations of high computational load and low efficiency were addressed by combining a Particle Swarm Optimization (PSO) algorithm with an Extreme Gradient Boosting (XGBoost) model. By learning from multiple samples generated by detailed simulation models, a surrogate model was established to improve prediction efficiency. Additionally, an improved sampling method was proposed to reduce the reliance of PSO-XGBoost on sample size. The results indicate that the machine learning surrogate model developed in this study better captures the impact of parameter uncertainty compared to traditional analytical-Monte Carlo methods such as Landsim. The predicted pollution concentration range is 1.36 times greater than that of conventional models. The PSO-XGBoost surrogate model, combined with the improved sampling method, outperforms other machine learning models in prediction accuracy (R²= 0.99) and stability, while reducing the computational time for model training by 70%, significantly improving the efficiency of uncertainty analysis. The application research based on this model shows that the probability of the characteristic pollutant COD exceeding the standard in the 10th year reaches 56.43%, and the possible distance of exceeding the standard is 54meters, indicating that there is a certain pollution risk in the study area. These findings provide an efficient and precise scientific method for analyzing landfill leakage risks and uncertainties and offer valuable references for further related research.

The primary parent material of tropical coral islands was coral sand, which was characterized by significant deficiencies in nitrogen retention capacity, particularly in terms of nitrate nitrogen (NO₃^--N) immobilization efficiency. This limitation was not only jeopardizes the sustainability of freshwater resources on these islands but also compromises the stability of coastal ecosystems. To promote the synergistic development of island-marine ecosystems, this study selected biochar (C), iron-modified biochar (FeC), and magnesium-modified biochar (MgC) were selected as soil amendments. These were combined with the native pioneer plant Ipomoea pes-caprae (P) to establish a collaborative remediation system. Experimental results demonstrated that MgC exhibited optimal NO₃^--N adsorption performance when applied individually, with its adsorption capacity and surface area-based adsorption capacity (SAC) exceeding those of FeC and C by 12.3%~28.6%. However, in plant-combined systems, a more sustained synergistic effect was demonstrated by the FeC-P combination, which maintained over 85% NO₃^--N retention rate throughout the experimental period. In contrast, performance decline was exhibited by the MgC-P system in later stages. Specifically, an 88.7% retention rate was achieved by the FeC-P group on day 40, which was 1.96-fold of the A-P group, 1.17-fold of the C-P group and 1.10-fold of the MgC-P group, respectively. Mechanistic analysis revealed that the electrical conductivity of coral sand was significantly increased by FeC (33.7%), and the proliferation of Patescibacteria was promoted (a 1.8-fold increase in relative abundance was observed), thereby strengthening the system's nitrogen transformation function. This physicochemical-biological synergistic optimization mechanism facilitated beneficial interactions between FeC and Ipomoea pes-caprae. Ultimately, a sustained enhancement of nitrogen retention capacity in coral sand was achieved. A novel technical pathway for the ecological restoration of coral islands was provided by the research outcomes.

Thorough mixing of contaminated soil and stabilizer is essential for effective ex-situ stabilization for heavy metals-contaminated soils. Field tests of ex-situ soil stabilization was conducted, and the total elements, moisture content, and leaching concentrations of target heavy metals (including arsenic(As) and antimony(Sb)) in the stabilized soils were measured. The influence of mixing equipment type, and soil-stabilizer mixing frequency on the ex-situ stabilization efficiency was evaluated. Based on the measured total elemental content and moisture content, a concept termed 'mixing uniformity' was proposed. The results showed the multi-function mixing equipment performed better than screening crushing bucket in controlling the uniformity of stabilizers in the contaminated soil. In contrast, the screening crush bucket significantly improved the uniformity of total As and Sb in the soil, with a larger mixing range. The mixing uniformities of total element content, moisture content, and As and Sb leaching concentrations increased with the number of mixing using the screening crushing bucket. When the number of mixing exceeded three, As and Sb leaching concentrations fell below remediation target values. Additionally, the uniformity of As and Sb leaching concentrations showed a good correlation with the uniformity of total contents. Based on the results, it is recommended that on-site rapid testing of total heavy metal content, combined with uniformity analysis, can be used to evaluate the mixing uniformity of contaminated soil and stabilizers during stabilization processes.

In view of the characteristics of Ultisols (red soils) in southern China, this study developed two types of rice-specific biochar-based fertilizers (BBOF: bio-organic-inorganic biochar-based fertilizer; BBF: inorganic biochar-based fertilizer) using rice straw biochar as the base and coating technology. Pot and field experiments were conducted to evaluate their effects on soil chemical properties, microbial communities and rice yield under different pH value, nutrient statuses, and cadmium (Cd) pollution levels. Conventional fertilizer (CF) was used as the control, with three carbon treatments for experiments: direct biochar application (BC), BBOF, and BBF. The results showed that both BBF and BC improved rice yield under field conditions, with BBF enhancing the three key yield components; however, BBF had limited effects on soil improvement. BBOF and BC significantly increased soil pH and soil organic carbon contents(SOC) in the weakly acidic (WA) soil and the strongly acidic soil (SA) with Cd pollution(P<0.05), demonstrating effective acid regulation and carbon sequestration, but had limited effects in low-nutrient acidic (LN) soils. The impact of carbon treatments on soil nutrients varied with soil type: in WA soils, all three treatments significantly increased available phosphorus (AP), available potassium (AK), and dissolved organic carbon (P<0.05); in SA soil, AK was significantly reduced (P<0.05); and in LN soil, ammonium nitrogen(NH₄⁺-N) and nitrate nitrogen levels were notably altered, with BC also significantly increasing AK content (P<0.05). Other soil properties showed no significant response to biochar treatments. Compared with BC, biochar-based fertilizers reduced the amount of exogenous biochar applied and thereby decreased soil Cd input, indicating higher environmental safety. Microbial community analysis revealed that none of the biochar treatments had significant effects on fungal communities (P>0.05), but all affected bacterial communities, with an impact intensity order of BC>BBOF>BBF and a soil bacterial communities response order of LN>SA>WA. Both BC and BBOF regulated bacterial communities in a similar way by significantly increasing the relative abundances of key phyla (Myxococcota, Methylomirabilota, and Acidobacteria) and important functional families (Rokubacteriales_unclassified, Anaeromyxobacteraceae, Bradyrhizobiaceae, and Nitrospiraceae), while significantly decreasing the relative abundances of Planctomycetota (phyla level) and Subgroup_7_unclassified and Isosphaeraceae (family level) (P<0.05). Correlation and redundancy analyses indicated that shifts in soil bacterial communities were closely related to changes in soil chemical properties, with different driving factors identified across soils: AP in WA, SOC in SA, and NH₄⁺-N in LN. This suggests that the regulatory effects of carbon treatments are highly soil-dependent. In conclusion, the bio-organic-inorganic biochar-based fertilizer demonstrated advantages in improving soil environmental conditions and regulating microbial communities in rice-growing red soils, showing potential to replace direct application of biochar. However, its yield enhancement effects and application strategies require further study and optimization.

Pyrolysis is an important process for efficient remediation of petroleum-contaminated soil (PCS), but how to reuse the obtained carbonized soil (RCS) has not received enough attention. In this study, RCS was treated by ball milling to activate its environmental catalytic components, and the obtained carbonized soil (RBCS) was used to activate peroxymonosulfate (PMS) oxidation to treat organic wastewater. The results showed that when the dosage of RBCS was 2g/L and the dosage of PMS was 1.5g/L, the removal rate of aniline (AN, 100mg/L) reached 99.9 %. Compared with RCS, ball milling treatment significantly improved the activation performance of RBCS for PMS oxidation. Quenching experiments and EPR tests showed that 、·OH、¹O₂ and environmental permanent free radicals (EPFRs) existed in the RBCS/PMS system. Electrochemical experiments show that there is also an electron transfer mechanism in the RBCS/PMS system. Ball milling exposes more metal oxides, amorphous carbon and oxygen-containing groups on the surface of carbonized soil. Metal oxides and oxygen-containing groups can activate PMS to produce reactive oxygen species to attack AN, while graphitized carbon and EPFRs may promote PMS oxidation by accelerating direct electron transfer to degrade AN. This study provides an environmentally friendly, value-added transformation strategy and treatment method for RCS, which is expected to have a good application prospect.

Representative Sb tailings from the northwest and southwest regions were selected to investigate the migration characteristics of Sb and arsenic (As), as well as changes in microbial community under both covered and exposed conditions. The results showed that the total concentrations of Sb-As in the Qinglong tailings were significantly higher than those in the Xihe soil-covered tailings, with Sb levels being 21.90~29.35 times higher and As levels 20.23~39.26 times higher. The index of Geo-accumulation (I_geo) and the Ratio of secondary phase to primary phase (RSP) indicated that the Qinglong tailings Sb-As contamination index was greater than 3, which belongs to severe contamination, the exposure of Sb-As thus poses a considerable threat to the soil environment. In contrast, the I_geo index for Sb-As in the Xihe soil-covered tailings were both <3, and RSP values was <2, indicating a relatively low level of contamination. Using the Wenzel sequential extraction method, the distribution of Sb-As fractions was found to follow the order: amorphous iron-aluminum oxide-bound fraction (F3)>residual fraction (F5)>crystalline iron-aluminum oxide-bound fraction (F4)>specifically adsorbed fraction (F2)>non-specifically adsorbed fraction (F1). F3 accounted for 36.91% and 37.00% of the total Sb-As contents, respectively. The bioavailable forms of Sb [Sb(Bio)] and As [As (Bio)] were significantly higher in the Qinglong tailings than in the Xihe soil-covered tailings. In Qinglong, Sb-As primarily occurred in the F3fraction, whereas in Xihe, they were mainly associated with the F5fraction. Principal coordinates analysis(PCoA) revealed that bacterial community structure varied across different environmental media. The dominant bacterial phyla in the Qinglong tailings were Chloroflexi and Firmicutes, with Kaistobacter, Pseudomonas, and Rhodoplanes as the predominant genera. In the Xihe soil-covered tailings, Gemmatimonadetes and Bacteroidetes were significant components, and Thiobacillus, Kaistobacter, and Sphingomonas were the dominant genera. Thiobacillus, Pseudomonas, Bacillus, Geobacter, and Sphingomonas were identified as key bacterial taxa enriched in long-term Sb-As contaminated environments, indicating their potential for application in in-situ ecological restoration of Sb tailings. The functional prediction using PICRUSt2 and Partial least squares discriminant analysis(PLS-DA)suggested that bacterial functional changes were primarily characterized by the enrichment of specific metabolic functions, accounting for approximately 40.66% of the total predicted functions. Spearman correlation analysis, Redundancy analysis (RDA), and Random forest (RF) analysis revealed that pH, soil organic matter (SOM), and water content (WAF) were the main drivers of bacterial community changes in the Xihe soil- covered tailings, while Sb-As concentrations and their chemical fractions were the main drivers of bacterial community structure and functional variation in the Qinglong tailings.

This study used Festuca arundinacea (tall fescue) as a pioneer plant for vegetation establishment on tungsten tailings to restore the tailings' soil multifunctionality index (SMF). The results showed that the application of chicken manure and biochar increased the available nitrogen (61.15%~61.48% and 23.55%~24.82%), available phosphorus (116.07%~143.50%), and organic matter content (55.46%~59.80% and 255.36%~263.27%) in the tailings. Chicken manure also increased the activities of urease (95.97%~117.03%), β-glucosidase (97.28%~112.59%), and phosphatase (31.11%~49.35%) in the tailings. These changes led to an increase in the SMF of the tailings, and the SMF was significantly correlated with the planting time of F. arundinacea (R² = 0.4260, P< 0.05). The amendments altered the bacterial community structure, with the community dissimilarity index between treatments increasing from 0.5437 to 0.7696 and then decreasing to 0.3496. The development of the bacterial community in the tailings showed convergence, attributed to the increase in the SMF. Co-occurrence network analysis of OUTs (operational taxonomic units) revealed that after the amendment treatments, the proportion of positively correlated edges decreased from 65.39% to 56.96%~61.85%, which enhanced the competitive relationships between bacteria and increased the complexity and sensitivity of the bacterial network. The structural equation model explained 89.1% of the changes in soil multifunctionality, with the direct effect of the amendments being 0.502. Additionally, indirect effects were generated through their impact on the fresh weight of F. arundinacea, bacterial diversity, and the co-occurrence network of OUTs.

In September 2023, a study was conducted in the Northeastern South China Sea to investigate the concentration distribution and mole composition of total dissolved amino acids (TDAA) in the seawater, as well as the sources and degradation status of dissolved organic matter (DOM). The results showed that the concentration of TDAA ranged from 0.37 to 2.59μmol/L, with an average value of (0.78±0.41) μmol/L. The horizontal distribution of TDAA exhibited a pattern of higher concentrations near the coast and lower concentrations in offshore, while the vertical distribution showed a gradual decrease from the surface to the bottom layer. Using D-alanine (D-Ala) as a biomarker, the contribution of bacterial organic matter to DOM (Bacterial-C%) was quantified. The Bacterial-C% in seawater ranged from 9.6% to 46.2%, with an average value of (23.3±8.1)%, demonstrating an overall trend of lower values near the coast and higher values in offshore areas. Additionally, the mean value of degradation index (DI) in surface seawater was (0.5 ± 1.0), while the average DI values for middle and bottom layers were (-1.2±0.6) and (-1.3±0.6), respectively. This indicates that the DOM in surface seawater was less degraded compared to those in the middle and bottom layers. This study elucidates the sources and degradation status of DOM in the Northeastern South China Sea, providing important scientific insights and data support for a deeper understanding of biogeochemical cycling processes in marginal seas.