Environmental Earth Sciences最新文献

Industrial solid wastes present severe disposal challenges, while hexavalent chromium [Cr(VI)]-contaminated wastewater threatens ecological and human health. This study developed a phosphogypsum-coal ash composite (MTPC) through synergistic mechanical-thermal activation to serve as a cost-effective impermeable liner for Cr(VI) environments. Orthogonal experiments assessed the influence of calcination temperature, duration, and Cr(VI) concentration on material’s performance. Optimal results were obtained at 700 °C for 120 min with a Cr(VI) concentration of 1 mg/L. The 28-day compressive strength reached 36.80 MPa, a 248.5% increase compared with the untreated samples. The Cr(VI) leaching concentration was reduced to 0.91 µg/L, while permeability coefficients as low as 2.66 × 10^− 8 cm/s. Microstructural and chemical characterization was performed using scanning electron microscope and energy dispersive X-ray spectroscopy (SEM-EDS), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Findings demonstrate that mechanical-thermal activation enhances the release and hydration reactions of active components in MTPC, promotes the formation of calcium silicate hydrate (C-S-H) gel and ettringite (AFt) crystals. These results highlight mechanical-thermal activation as an effective and practical approach to valorize industrial wastes into sustainable, high-performance cementitious materials for environmental protection.

The Mannarkad Watershed is a subtropical mountain catchment in the Western Ghats, Kerala, facing critical soil erosion issues due to climate change and anthropogenic activities, which cause adverse impacts on soil infertility and agricultural productivity. This study investigates the spatio-temporal variability of soil erosion rate (SE) and erosion hotspots for 2000, 2010, and 2023 using the GIS-based Revised Universal Soil Loss Equation (RUSLE) model. Sediment yield estimates were derived at detailed spatial scales using the Sediment Delivery Ratio (SDR) method. The results show that annual soil erosion rates have grown from 14.9 t/ha in 2000 to 23.02 t/ha in 2023, occurring in the sloped upland valleys and foothills across the watershed have seen the most severe erosion. Wherein, rainfall erosivity is at a higher rate of 1129–1669 MJ·mm/ha·hr·yr in 2000, and 2344–3076 MJ·mm/ha·hr·yr in 2023, causing sediment transport towards downslope and deposited along the valley fills and channel levees. Over the last two decades, the findings revealed that the erosion rate has progressively increased in various hotspots owing to rainfall variability and land-use changes. The RUSLE model exhibits that the erosion hotspots, mainly found in middle laterite plateaus, and sparsely vegetated uplands, consist of steep-sloped valleys, upland stream orders, barren lands, down-sloped fallows and proximity of built-up areas. Significantly, the sediment yield is at a higher rate (0.27–23.81 t/ha/yr) in the valley fills, downpour streams of the foothills, with an average rate of 6.75 t/ha/yr, contributing to alluvial plains and channel levees. The RSULE model calculates the AUC value of 0.823 based on the spatial correlation of eroded sites of GPS survey and map-derived data, indicating the model’s reliable predictability. The sediment yield was validated with rain gauge-based sedimentation data from the Kanjirapuzha Dam station, showing close agreement with the derived SDR rate (predicted 2.79 t/ha/yr vs. observed 5.8 t/ha/yr). GIS-based RUSLE–SDR is widely used for soil erosion rate and sediment yield at the pixel scale, and in heterogenic landscapes, and lacks this in other conventional approaches. However, the output of this model is subject to uncertainties that depend on the quality of input parameters, scale, and resolution. Despite these limitations, the outcomes provide a spatio-temporal pattern of soil erosion and sediment yield and are a valuable database for soil and water conservation planning and management activities.

With the deepening of groundwater resource development and deep mineral resource exploitation, the complexity of fluid seepage and solute transport in fractured rock masses has become increasingly prominent, especially the migration and evolution mechanisms of fracture water chemistry under high-temperature and high-pressure conditions remain unclear. This study explored the laws of sulfate evolution and radon migration under fracture seepage conditions by establishing a multi-factor coupling experimental system, and further deepened the analysis of their internal mechanism of action. Research results showed that an increase in temperature accelerated sulfate generation by increasing the kinetic rate of sulfide oxidation, while it enhancing the thermal motion of radon molecules and significantly increasing the radon migration rate; Increased confining pressure compressed the equivalent hydraulic aperture of fractures, which in turn reduced the reaction interface between sulfides and fluid and increased seepage resistance, thereby resulting in a reduction in sulfate production; The influence of flow rate on sulfate concentration was primarily manifested as a competitive mechanism involving “oxygen supply” and “oxidation time”. Under most operating conditions, the inhibitory effect (caused by increased flow rate shortening fluid residence time) played a dominant role, resulting in a reduction in sulfate concentration; Mineral composition served as the material basis for the migration of sulfate and radon. The sulfate concentration in the fracture seepage fluid of pyrite was much higher than that in limestone, and the RaSO₄ complexes formed by SO₄²⁻ and Ra(radium) led to a significant increase in the concentration of radon generated by decay in the seepage fluid. This study provides important experimental data and theoretical support for numerical simulations of fracture water chemistry and radon migration, as well as environmental risk assessment in deep mining settings.

Submarine groundwater discharge (SGD) and its influence on coastal acidification and trace-metal enrichment have not been studied in Borneo. This study characterizes SGD from northwest Borneo into the South China Sea, focusing on iron (Fe) and aluminum (Al) inputs, hydrogeochemical controls on their mobility, and SGD’s role in coastal acidification. Samples were collected along transects at Tungku and Empire beaches, spanning the peritidal to subtidal zones, as well as from streams, pools, and beach sand. SGD contained elevated Fe and Al (Tungku: 4.07 mg/L Fe, 1.31 mg/L Al; Empire: 2.12 mg/L Fe, 0.38 mg/L Al), identifying these as key SGD-derived trace metals. pH was near-neutral in many samples (minimum 6.6), rising from 7.72 (Tungku) and 7.48 (Empire) in SGD to 8.11 and 8.01 in adjacent seawater, creating steep pH gradients favoring Al and Fe precipitation. Acid sulfate soils and high dissolved organic matter enhance groundwater acidity and trace-metal mobility. Major-ion chemistry indicates dominance of non-carbonate alkalis (SO₄²⁻ + Cl⁻ >CO₃²⁻ + HCO₃⁻; Na⁺ + K⁺ >Ca²⁺ + Mg²⁺) and low phosphate and nitrate, with mixed freshwater–saline contributions. The combination of low pH, elevated Fe and Al, and anthropogenic disturbance may degrade coastal and groundwater quality, affecting marine biogeochemical cycles, biodiversity, and ecosystem functioning. Overall, SGDs in Brunei deliver acidic, Fe- and Al-enriched water, contributing to coastal acidification and contamination, with implications for regional climate resilience.

Mapping permafrost distribution is significant for comprehending the impacts of climatic alterations and providing baseline data for delineating permafrost-induced hazard potential areas in high mountainous regions in the Himalayas. This study investigates the spatial distribution of permafrost in the Garhwal Himalaya, Uttarakhand, by integrating topo-climatic variables and rock glacier inventories using three machine learning algorithms: Binary Logistic Regression, Random Forest, and Extreme Gradient Boosting (XGBoost). A total of 268 rock glaciers comprising 247 active and 21 relict forms were mapped using high-resolution imagery from Sentinel-2 and Google Earth. Logistic regression models were developed based on key predictor variables, including mean annual air temperature (MAAT), mean annual ground temperature (MAGT), land surface temperature (LST), snow cover duration, potential incoming solar radiation (PISR), and slope aspect. The Random Forest and XGBoost models incorporated extreme air temperature, elevation, and the mean temperature of the warmest quarter (MTOWQ) to better capture the spatial variability of permafrost. The logistic regression models (LRM-MAAT, LRM-MAGT, LRM-SC, and LRM-LST) demonstrated classification accuracies of 94.8%, 91.8%, 92.05%, and 91.4%, respectively. The Random Forest and XGBoost models outperformed the regression models, achieving testing accuracies of 97.6% and 97.0%, respectively. Validation using the Permafrost Zonation Index map showed strong similarity among all models with adequate accuracy indicating the applicability of these models for permafrost distribution modeling in the Himalayas. (Keywords: Garhwal Himalaya, Logistic Regression Model, Permafrost, Random Forest ML, Rock Glacier, XGBoost ML)

Nitrate contamination of groundwater is a growing global concern, with severe health and environmental consequences, particularly in arid and semi-arid regions where groundwater is the primary water resource. This study investigates the extent and risk of nitrate pollution in the Southern Gabes aquifers, south-eastern Tunisia, addressing the research question: To what extent are these aquifers vulnerable to nitrate contamination, and what areas are most at risk? The conceptual framework integrates hydrogeological vulnerability assessment with spatial pollution risk modeling. Methodologically, the study employs the Intrinsic Vulnerability Index (IVI), Nitrate Pollution Index (NPI), Groundwater Nitrate Sensitivity Index (GNSI), and Groundwater Nitrate Pollution Risk Index (GNPRI), combined with geospatial analysis. The IVI indicates that 71.42% of the region faces moderate nitrate contamination risk, while only 0.36% shows negligible vulnerability, with 50 mg/L set as the critical drinking water threshold. Spatial correlation analyses reveal that areas of high nitrate concentration overlap with zones of intensive agricultural nitrate application. The integrated GNPRI highlights that 60.91% of the aquifer system has medium sensitivity to nitrate pollution, with 0.25% classified as highly sensitive. These findings not only identify priority zones for intervention but also provide an evidence-based framework for decision-making in groundwater protection. The implications of this research extend beyond regional boundaries, offering a transferable methodology for sustainable groundwater management in water-scarce environments worldwide.

This study examines the distribution of mercury in the brine, plankton, and bottom sediments of Lake Bolshoye Yarovoye. In inorganic complexes, mercury predominantly occurs as HgCl₄²⁻ and Hg(SR)₂. Within pore waters, mercury is mainly present as MeHgSR–DOM rather than MeHgCl. The accumulation of mercury in bottom sediments results from the precipitation and dissolution of Fe and Mn oxides and oxyhydroxides. The geochemical behavior of mercury in sediments is influenced by various sulfur species, including S(VI), S(II), and pyrite, which can restrict the bioavailability of mercury and affect the formation of MeHg. A strong correlation is observed between the distribution of Hg–OM and S(II) within the upper 50 cm of the sediment column. Vertical migration of anthropogenic mercury within the sediment core has been detected, facilitated by the high water content. At a depth of 110–120 cm, a geochemical barrier is formed, representing a zone of active transformation of mercury species. A moderate level of mercury contamination was recorded in the bottom sediments and in the plankton Artemia salina within the impact zone of the “Altaikhimprom” plant.

Artisanal mining is common in many developing and underdeveloped countries and is a major source of livelihood for communities in mining areas. This activity is also a major cause of environmental deterioration in many parts of Africa, Asia and South America. Over the years, Penhalonga, a small town in Zimbabwe has seen the rise of artisanal miners, mostly practicing alluvial panning. The artisanal mining activities in Penhalonga have resulted in environmental problems such as land degradation and pollution. This study aims to investigate how artisanal mining has impacted the land cover changes in Penhalonga, particularly, how vegetation and water have been impacted. This was achieved by using the XGBRFClassifier to analyze Landsat images (representing a 30-year period) of the study area on Google Earth Engine. This study revealed that Penhalonga is predominantly covered by vegetation but has been negatively impacted as artisanal mining consistently expanded. Between 1993 and 2003, 116 hectares (16.5%) of Vegetation were converted to Artisanal Mines, between 2003 and 2013, 78 hectares (11.8%) of Vegetation were converted to Artisanal Mines and 117 hectares (18%) of Vegetation were converted to Artisanal Mines between 2013 and 2023. These changes pose a serious threat to the Penhalonga community, which relies on agriculture and forestry, both of which have suffered due to expanding mining activities. A review of Zimbabwe’s mining policies revealed a lack of specific guidelines for artisanal mining, presenting a major challenge to sustainability. This study offers recommendations for promoting sustainable artisanal mining practices to mitigate environmental degradation while supporting local livelihoods.

Atmospheric deposition of persistent toxic substances represents a potential threat to pristine mountain ecosystems, where precipitation and meltwater from snow and glaciers are essential components of downstream water supply. We investigated the concentrations of polycyclic aromatic hydrocarbons (PAHs) in surface waters of the western Tianshan Mountains in Kyrgyzstan, and used n-alkane and water isotope values (δD and δ¹⁸O) to elucidate PAH sources and the factors that influence their distributions. PAH concentrations in lake and river waters were 21.00 − 68.05 ng L^–1 and 13.84 − 81.57 ng L^–1, respectively, with high fractions of low-molecular-weight (LMW) compounds. Based on n-alkane profiles and a positive matrix factorization (PMF) model, we determined that PAHs in the study area originated from biomass combustion (42.8%), petroleum input (23.6%), vehicle emissions (16.3%) and coal burning (17.3%). Highly contaminated sites, with greater abundance of heavy compounds and higher stable isotope values, were closer to large settlements, indicating contributions from local human impacts on the PAH loads in waters. Elevated LMW-PAH concentrations in river waters with more negative isotope values, and altitude-dependence of LMW congeners, indicated that atmospheric deposition is responsible for the spatial distribution of more volatile PAHs. Risk estimation suggests possible effects of PAHs on ecosystem biota, but negligible non-carcinogenic and carcinogenic effects on humans, from either dermal contact or water ingestion.

Accurate identification of geochemical features in coalbed methane (CBM) well-produced water is vital for evaluating the gas potential of reservoirs. However, fracturing fluid interference with water chemistry and productivity analysis is a challenge. This study reveals the origin of produced water ions and their control mechanisms on productivity in CBM wells, based on hydrochemical data from 31 CBM wells in the Gujiao Block, Xishan Coalfield, China. To extract original reservoir information, we established quantitative identification criteria for fracturing fluid contamination (Cl⁻ < 70 meq/L and K⁺ + Ca²⁺ + Mg²⁺ < 2.5 meq/L), effectively excluding 29% of contaminated samples. Analysis of the water origin and system conditions indicated that the dominant Cl-Na water results from salt dissolution and cation exchange. Ba²⁺-Sr²⁺ enrichment reflects a marine-terrestrial transitional environment in the Taiyuan Formation, while δD-δ¹⁸O indicates slow water circulation, with CBM water mainly sourced from sandstone. The produced water in the study area mainly comes from the Member 3 Formation sandstone aquifer. The synergistic effects of SrSO₄-BaSO₄ precipitation in microfractures, as well as the enrichment and fractionation of hydrogen and oxygen isotopes in high hydrodynamic zones, are the main controlling factors for low productivity. Under weak hydrodynamics, cation exchange, microbial dissolution, sulfate reduction, and CO₂ dissolution enrich Na⁺-HCO₃⁻-TDS-Li⁺, enhancing gas well productivity. Ultimately, by integrating these hydrochemical parameters, the ion evolution pathways in wells with different production capacities were analyzed, and a geochemical mechanism model for CBM water production control was constructed. This research provides a crucial hydrochemical evaluation basis for the efficient development of CBM.