Microplastics (MPs) are emerging subsurface contaminants, yet their occurrence and transport potential in nearshore aquifers connected to large freshwater lakes remain poorly understood. This study characterized MPs in nearshore aquifers surrounding Taihu Lake using laser direct infrared (LDIR) spectroscopy and quantified their potential fluxes to the lake via lacustrine groundwater discharge (LGD) with a 222Rn-based model. MPs were detected in all ten shallow groundwater samples, with abundances ranging from 176 to 1526 particles/L (mean ± SD: 576.9 ± 404.6 particles/L). A total of 22 polymer types were identified, dominated by silicone, fluororubber, and chlorinated polyethylene, suggesting mixed domestic, industrial, and tourism-related sources. MPs were predominantly fine (< 50 μm) fragments, a size-shape combination favoring transport through porous media. Under three size-dependent transport scenarios, first-order, dry-season baseline LGD-derived MP loads were estimated to range from 1339 ± 966 to 3560 ± 2738 trillion particles/yr by number and from 6.1 ± 6.9 to 57.0 ± 49.8 tons/yr by mass. For the 20-50 μm fraction, the LGD-derived loads were of the same order of magnitude as the estimated annual riverine input. Although these estimates are subject to substantial uncertainty, these findings highlight the widespread presence of MPs in lakeshore shallow groundwater across a humid floodplain basin, and suggest that LGD could represent a previously underrecognized pathway for the transport of fine MPs to shallow lakes. This underscores the need to incorporate groundwater-surface water connectivity into future plastic pollution assessments.

In the Wanshan mining watershed, erosion is an important surface process transporting mercury contaminants from soil to river, posing substantial pollution risk to ecosystem. The erosion-driven mercury pollution is influenced by rainfall, soil erodibility, vegetation coverage, topography, mercury pollutant, and human activity. Quantifying the contribution of these factors is vital to evaluate erosion-driven mercury pollution. Previous studies over-relied on expert-based subjective method to assess factor contributions, yielding discrepancies between mercury pollution risk and observed fluvial contamination. Here, this study applied the CRITIC method to quantify objective factor contributions. Results indicate that rainfall, human activity, and mercury pollutant predominantly determine pollution risk, with contribution of 28 %, 20 %, and 18 %, respectively. Based on objective contribution results, we develop a novel risk index to evaluate mercury pollution. The evaluated mercury pollution risk and observed fluvial mercury contamination show a consistent distribution pattern. These findings provide effective reference for pollution control within mining watersheds.

In situ chemical oxidation (ISCO) using controlled-release oxidants materials (CRMs) is an effective method for the long-term removal of organic pollutants from groundwater. However, the complex hydrodynamic characteristics of groundwater make it extremely challenging to elucidate the mechanisms of pollutant degradation through CRMs. This study aims to construct persulfate-based CRMs using mesoporous MnO2 (Mn-CRMs) and TiO2 (Ti-CRMs) as catalysts to degrade tetracycline (TC) under static and dynamic groundwater. The types and contributions of active species, stoichiometric efficiency of the reactions, TC degradation pathways of the CRMs were compared in the static and dynamic groundwater. The results revealed the active species in the CRMs-based TC degradation depending on the structures of the powder catalysts. In the static and dynamic groundwater, the contribution rate of ·OH and SO4·- in the Mn-CRMs-based TC degradation was nearly 100 %, indicating a complete radical-based degradation pathway. TiO2 with abundant oxygen vacancies produced abundant 1O2 during the PDS activation process. Ti-CRMs showed a contribution rate of 1O2 to the TC degradation of up to 32.05 %, which indicated the co-action of ·OH and 1O2 for degrading TC. The RSE values of the CRMs-based TC degradation were similar to those of TC degradation using powder catalysts. Since the groundwater flow and PDS release, lower PDS concentrations were maintained around the CRMs in the dynamic groundwater, resulting in a higher RSE value. The results in this study provide insights into the removal mechanisms of pollutants in different groundwater and expand the application of ISCO to groundwater remediation.

The geochemical fate of heavy metals in mining regions is significantly complicated by the coupled effects of residual flotation reagents and the co-existence of multiple metals. Combining column transport experiments and spectroscopic characterization, this study developed a Multisurface Speciation Model (MSM) to describe the reaction processes between cadmium (Cd), lead (Pb), and zinc (Zn) and key retention components including iron oxides, organic matter, clay minerals, and ethyl xanthate (EX), to quantitatively elucidate the impact of system complexity and EX-loaded concentration on their transport and retention behaviors in actual porous media. First, increasing the EX-loaded concentration from 0 to 1 mmol/L enhanced overall retention and inhibited the transport of all the three metals. Conversely, increasing system complexity from single-metal to multimetal systems diminished overall retention and enhanced transport. EX loading established EX as a dominant component for metal retention and concurrently suppressed the retention contribution of other soil components. However, the transition from single metal systems to ternary metal systems led to the intensified competition between metals and EX, thereby reducing the adsorption of EX onto the porous media and consequently weakening its overall capacity to retain the heavy metals, with the EX-retained concentrations of Cd, Pb, and Zn decreasing by 78.62 %, 52.44 %, and 80.46 %, respectively. The characterization results demonstrated that while the introduction of EX enhanced heavy metal retention through introducing new sulfur-containing functional groups, increasing the net negative surface charge, and promoting metal-immobilizing sulfidation reactions, the enhancement was significantly offset in multimetal systems by the intensified inter-metal competition and by a concurrent weakening of electrostatic attraction. This study successfully deconvolved the dual effects of EX loading and multimetal competition on the transport and retention of Cd, Pb, and Zn, offering a new perspective on the fate of heavy metals in xanthate-affected systems.

Lake eutrophication driven by excessive nutrient inputs has become a global issue, but the potential impact of lacustrine groundwater discharge (LGD) as a nutrient source on lake eutrophication remains largely unknown. This study assessed the contribution of LGD-derived nutrient loads and revealed their potential impact on lake eutrophication in Taihu Lake, a typical large shallow and eutrophic lake in China, based on the segmented radon mass balance model and nutrient data. The total LGD flux was estimated to be 6.59 × 109 m3 a-1, representing 57.8 % of the annual flux from inflowing rivers. LGD was a significant hidden nutrient source, contributing total nitrogen (TN) and total phosphorus (TP) loads to the entire lake comparable to those of the inflowing rivers. Dissolved inorganic forms dominated these LGD-derived nutrient loads. Spatially, the majority of TN (59.9 %) and TP (62.4 %) loads derived from LGD originated from sub-area III (southwest), which differed from the dominant area of riverine inputs, sub-area II (northwest). In addition, the significant enrichment of nitrogen observed in LGD suggests its potential to mitigate nitrogen limitation in the lake. The increasing nitrogen limitation in Taihu Lake and the prevalence of nitrogen limitation in eutrophic lakes worldwide indicate that nitrogen is a key nutrient in managing LGD-derived nutrient loads. This study highlights the importance of integrating LGD-derived nutrient loads into nutrient reduction strategies to reverse eutrophication in large eutrophic lakes, especially those with nitrogen limitation.

Accurately simulating immiscible counter-current flow is crucial for applications from geological CO2 storage to shale gas production, yet it remains a major challenge for conventional pore network models (PNMs), which are unable to handle the numerical instability of opposing flows. To address this critical gap, we developed a novel dynamic PNM that incorporates a ‘transition state’ algorithm. This method successfully eliminates the spurious meniscus oscillations that hinder traditional models, enabling robust simulation of the complete counter-current process. Using this model, we quantify the profound impact of pore structure on flow efficiency. Our results demonstrate that increasing the pore size distribution uniformity (Weibull shape factor k from 0.5 to 3.0) extends the persistence of continuous air outflow pathways by more than six-fold (from 359 to over 2300 simulation steps). This leads to a quantifiable increase in the initial fluid exchange rate by nearly 10 times (from 10−11 to 10−10 m3/s) and a reduction in final residual air saturation by 53% (from 0.91 to 0.43). This work provides a tool for predicting and optimizing counter-current flow efficiency in subsurface engineering applications.

The removal of trace amounts of antibiotics from water environments while simultaneously avoiding potential environmental hazards during the treatment is still a challenge. In this work, green, harmless, and novel asymmetric mesoporous TiO2 (A-mTiO2) was combined with peroxodisulfate (PDS) as active components in a controlled-release material (CRM) system for the degradation of tetracycline (TC) in the dark. The formation of reactive oxygen species (ROS) and the degradation pathways of TC during catalytic PDS activation by A-mTiO2 powder catalysts and the CRMs were thoroughly studied. Due to its asymmetric mesoporous structure, there were abundant Ti3+/Ti4+ couples and oxygen vacancies in A-mTiO2, resulting in excellent activity in the activation of PDS for TC degradation, with a mineralization rate of 78.6%. In CRMs, ROS could first form during PDS activation by A-mTiO2 and subsequently dissolve from the CRMs to degrade TC in groundwater. Due to the excellent performance and good stability of A-mTiO2, the resulting constructed CRMs could effectively degrade TC in simulated groundwater over a long period (more than 20 days). From electron paramagnetic resonance analysis and TC degradation experiments, it was interesting to find that the ROS formed during PDS activation by A-mTiO2 powder catalysts and CRMs were different, but the degradation pathways for TC were indeed similar in the two systems. In PDS activation by A-mTiO2, besides the free hydroxyl radical (·OH), singlet oxygen (1O2) worked as a major ROS participating in TC degradation. For CRMs, the immobilization of A-mTiO2 inside CRMs made it difficult to capture superoxide radicals (·O2−), and continuously generate 1O2. In addition, the formation of sulfate radicals (·SO4−), and ·OH during the release process of CRMs was consistent with PDS activation by the A-mTiO2 powder catalyst. The eco-friendly CRMs had a promising potential for practical application in the remediation of organic pollutants from groundwater.

The heavy metal pollutant Cr(Ⅵ)has high toxicity and strong mobility,posing a great threat to groundwater safety.The cunent relevant soil standards often overlook groundwater safety.It is urgent to establish a Cr(Ⅵ)soil environmental reference value based on groundwater safety in order to provide support for the supervision of contaminated sites.In order to determine the calculation method of soil environmental reference value for groundwater protection that is in line with China's characteristics,research and derivation of soil environmental reference value based on groundwater safety at home and abroad,and draw reference from foreign methods for formulating environmental reference value of pollutants based on groundwater safety.Taking Zhejiang clay loam,Jiangsu loamy sandy soil and Jilin loamy clay as research objects,the distribution coefficients of Cr(Ⅵ)in the three soils were obtained through indoor static adsorption tests.The soil parameters and aquifer-related parameters of the three soils were obtained through literature research,The soil screening level(SSL)method proposed by the United States Environmental Protection Agency in the Soil Screening Guidelines was adopted,based on groundwater quality standards(GBT14848-2017),a soil environmental reference value aiming at groundwater protection is obtained.The results show that the baseline values of Cr(Ⅵ)soil environment based on groundwater safety were 0.944 0.690,0.514 mg/kg,respectively.The results are close to the reference values of foreign countries for the purpose of protecting groundwater safety.However,the differences of soil properties in each study area make the final base values different.Therefore,when improving the soil environmental quality system,local regulatory agencies should build a database of soil and aquifer parameters to help soil pollution control.The research results can provide scientific basis for deducing the environmental reference value of heavy metal soil based on groundwater safety in various regions of China.

Differences in electrical properties of media are the basis for determining the type and extent of contamination using geophysical methods. However, differences in heavy metals and organic matter complicate the electrical properties of compound -contaminated media, and existing geophysical methods cannot independently identify compound contamination. Therefore, this study proposes a geophysical detection system that combines electrical resistance tomography (ERT) and induced polarization methods and establishes a solid theory as the basis for the system application through laboratory experiments, model analysis, and site applications. The study reveals that as the organics volume proportion increases, the resistivity and normalized chargeability of contaminated media increased slowly, followed by a rapid increase, and finally reached a stable state. The specific type of compound significantly influences the electrical properties, while the resistivity of different kinds of compoundcontaminated media reaches the same maximum value as the organics volume proportion increases. The medium type determines the contaminated media's lower resistivity limit and upper normalized chargeability limit. Additionally, the interplay between heavy metal type, content, and medium complicates the electrical properties of the media, with the compound type exerting a significant impact on resistivity. Archie's law and random forest modeling reveal that the inflection point for resistivity change occurs at 40 % and 80 % organics volume proportions, while the inflection point for normalized chargeability change occurs at 30 % and 70 % organics volume proportions in compound -contaminated media. These inflection points depend on the types of compounds, compositions, proportions, and media, and their importance for the electrical properties of the media changes with the increasing organics volume proportion. Based on the changing patterns of resistivity and normalized chargeability in heavy metal -organic compound contaminated media, the modified geophysical detection system can effectively identify the pollution type and intensity, which provides accurate pollution information to develop effective treatment strategies.

In mining regions, flotation reagents can interact with heavy metals, thereby increasing the complexity of their migration. However, most current studies solely focus on the migration of heavy metals, neglecting the influence of flotation reagents in their models concerning mining area pollution. This study developed the reactive transport model, Multisurface Speciation Model (MSM), which integrated the reaction processes of the three main soil components (iron oxides, organic matter, clay minerals) and ethyl xanthate (EX), a typical flotation reagent, with cadmium (Cd2+) to investigate the effects of EX on the transport and retention of Cd2+ in natural porous media under varying pH conditions. The study revealed that EX formed new adsorption sites for Cd2+, enhancing its retention and inhibiting transport with increased EX loading (0 to 2.5 mmol center dot L-1), while higher pH levels (ranging from 4 to 8) further strengthened the retention capability of Cd2+. The MSM further predicted the solid-phase concentration distribution of Cd2+ among various components. With increasing EX-loaded concentrations, xanthate became the dominant adsorbing component, accounting for 48.93 % to 95.31 % of adsorption, and competitively interacted with other components. Xanthate retention was lower under acidic conditions compared to neutral and alkaline environments. Sensitivity analysis highlighted the concentrations of iron oxide adsorption sites (SurfaOH, SurfbOH) as critical parameters in the models, underscoring the need for precise determination of soil physicochemical indicators. This study stressed the crucial role of flotation reagents and pH conditions in controlling heavy metal mobility, offering important insights for environmental management in mining regions.

Aiming at the effective remediation of antibiotic contaminants in groundwater, in-situ chemical oxidation (ISCO), using controlled release materials (CRMs) as an oxidant deliverer, has emerged as a promising technique due to their long-term effective pollutant removal performance. This study used different microstructures of mesoporous manganese oxide (MnOx) and sodium persulfate as active components to fabricate CRMs. Following that, a comparative study of tetracycline (TC) degradation and the formation of reactive oxygen species (ROS) by mesoporous MnOx powder and CRMs were conducted. The ROS formed during peroxodisulfate (PDS) activation by powder catalysts and CRMs differed, but MnOx powder catalysts and CRMs both had good reaction stoichiometric efficiency (RSE) for PDS, thus completely mineralizing TC. In PDS activation by mesoporous MnOx powder, oxygen vacancies (OVs) caused by defects in the catalysts contributed to the generation of singlet oxygen (1O2). The 1O2 and free radicals (·SO4- and ·OH) both worked as major ROS participating in TC degradation. Concerning the release of CRMs in static groundwater, the immobilization of catalysts inside CRMs made it difficult to release 1O2 in the solution, thus slowing the degradation of TC by CRMs containing MnOx(1) in static groundwater. In the TC remediation in dynamic groundwater, the water flowing slowly passed through the CRM layer, and TC molecules were trapped. Therefore, 1O2 degraded the trapped TC in the CRM layer in dynamic groundwater. Compared to TC, the toxicity of most intermediates during the TC degradation by CRMs has decreased in static and dynamic groundwater.

Air-water two-phase flow is a common phenomenon during irrigation or intense rainfall in soils. The competition between air and water phases has been recognized for long, but few attempts have been made to study the effect of pore size distribution on the air-water displacement processes at pore scale. In this study, micro-computed tomography experiments and pore network simulations are employed to study air-water flow in the pore space. Experimental and simulated results show that as the water saturation changes, the diameters of water-occupied pores change more quickly than air-occupied pores, while the connectivity of air clusters is more fragile than water clusters. Compared with single-phase conditions, air-water two-phase flow is more sensitive to pore network connectivity. It can also be found that, due to the decreasing diameter of water-occupied pores and decreasing connectivity of air clusters, the air-water flow rate decreases as the pore size distribution becomes skewed.

Controlled release materials (CRMs) are an emerging oxidant delivery technique for in-situ chemical oxidation (ISCO) that solve the problems of contaminant rebound, backflow and wake during groundwater remediation. CRMs were fabricated using ordered mesoporous manganese oxide (O-MnOx) and sodium persulfate (Na2S2O8) as active components, for the removal of antibiotic pollutants from groundwater. In both static and dynamic groundwater environments, persulfate can first be activated by O-MnOx within CRMs to form sulfate radicals and hydroxyl radicals, with these radicals subsequently dissolving out from the CRMs and degrading tetracycline (TC). Due to their excellent persulfate activation performance and good stability, the constructed CRMs could effectively degrade TC in both static and dynamic simulated groundwater systems over a long period (>21 days). The TC removal rate reached >80 %. Changing the added content of O-MnOx and persulfate could effectively regulate the performance of the CRMs during TC degradation in groundwater. The process and products of TC degradation in the dynamic groundwater system were the same as in the static groundwater system. Due to the strong oxidizing properties of sulfate radicals and hydroxyl radicals, TC molecules were completely mineralized within the groundwater systems, resulting in only trace levels of degradation products being detectable, with low- or non-toxicity. Therefore, the CRMs constructed in this study exhibited good potential for practical application in the remediation of organic pollutants from both static and dynamic groundwater environments.

During intense rainfall or flood irrigation, air may be compressed below the wetting front in the unsaturated zone, which reduces infiltration and thereby leads to excessive runoff and soil erosion. However, estimation of the critical infiltration rate (Icrit) that leads to air compression remains difficult. In this study, the critical infiltration rate for air compression was investigated experimentally and analytically. During infiltration experiments, significant air compression was observed as the infiltration rate excessed some critical rate for the working sands. And this measured critical rate increased as particle size of the sand increased. An innovative analytical approach was then proposed to estimate the values of Icrit using the parameters of the sands. When taking the impedance of air into consideration, the estimated Icrit matched well with the measured Icrit in the experiments. Based on the analytical approach, an equation was proposed to predict Icrit for a porous medium. According to the equation, the value of Icrit was determined by the permeability and pore size distribution of the porous medium. It was found that Icrit increased with the permeability of the porous medium, and also increased as the pore size of the medium became more uniform.

Experiments were carried out to investigate the effect of infiltration flux on air counterflow in a 2-dimensional (2-D) confined sand chamber. The air saturation distribution was monitored using light transmission and the air pressure was measured by manometers. As infiltration flux increased to 1000 mL/min and 1100 mL/min, significant increase in air pressure was observed. Due to the increase of air pressure, water infiltration was retarded, leading to a significant decrease in air outflow rate at high infiltration flux. When the infiltration flux was larger than 800 mL/min, the air flowed out of the sand chamber in the form of air "fingers". The underlying process of the finger-like air outflow pattern was analyzed quantitatively, and the critical infiltration flux leading to air "fingers" was estimated based on the relative air/water permeability of the working sand. The Green-Ampt model showed that the infiltration process was retarded by air counterflow when the air pressure head was comparable to the depth of the wetting front at high infiltration flux.

In the present study, the moisture distribution on the wetting front during drainage and imbibition in a 2D sand chamber is studied thoroughly. Based on the high-resolution data measured by light transmission method, the moisture distribution is observed and then analyzed quantitatively. During drainage and imbibition, different moisture distributions are observed: (a) during drainage, moisture contents fluctuate in a larger range and fingers can be seen on the wetting front; (b) while during imbibition, moisture contents fluctuate in a smaller range and the wetting front is more regular. The Hurst coefficients are successful in capturing different characteristics of the moisture distribution between drainage and imbibition. During imbibition, the Hurst coefficients are around 0.2 on the wetting front; while during drainage, the Hurst coefficients are around 0.5. As the porosity changes from 0.336 to 0.383, the moisture distribution in the sand chamber does not display obvious change. While as the imbibition rate increases from 5 ml/min to 400 ml/min, the moisture distribution on the wetting front becomes more uniform.

Inter-basin water transfer projects (IBWTPs) can involve basins as water donors and water receivers. In contrast to most studies on IBWTPs, which mainly impact the surface-water eco-environment, this study focuses on the impacts of an IBWTP on groundwater and its eco-environment in a water donor basin in an arid area, where surface water and groundwater are exchanged. Surface water is assumed to recharge groundwater and a groundwater numerical simulation model was constructed using MODFLOW. The model was used to quantitatively evaluate the impact of an IBWTP located in the upstream portion of Nalenggele River (the biggest river in the Qaidam basin, Northwest China). The impact involved decrease in spring flow, drawdown of groundwater, reduction in oasis area, and an increase in species replacement of oasis vegetation in the midstream and downstream of the river. Results show that the emergence sites of springs at the front of the oasis will move 2–5 km downstream, and the outflow of springs will decrease by 42 million m3/a. The maximum drawdown of groundwater level at the front of the oasis will be 3.6 m and the area across which groundwater drawdown exceeds 2.0 m will be about 59.02 km2, accounting for 2.71% of the total area of the oasis. Under such conditions, reeds will gradually be replaced by Tamarix, shrubs, and other alternative plant species. These findings have important implications for the optimization of water resource allocation and protection of the eco-environment in arid regions.

江苏省地处我国东部沿海,为我国经济最发达的地区之一,地热水资源较为丰富,地热水资源开发前景广阔,科学的开发利用好地热水资源对缓解能源压力、节能减排、保护生态环境,促进江苏低碳经济的发展具有十分重要的意义[1].本文对江苏省178口地热井与温泉基本情况进行调查,并收集大量资料进行计算分析,对全省热储分布特征,微量元素的分布与区域地质背景之间关系以及其受水岩相互作用等条件的影响进行研究.结果表明,江苏省可按构造及地层特征划分为四大地热资源区,区内地热化学类型主要为HCO3-Na、Cl-Ca、Cl-Na、SO4-Ca、SO4-Na,地热水的矿化度范围为297~2 1087 mg/L,pH值范围为6.59~9.17.地热水微量元素以氟化物、锶、偏硼酸、偏硅酸四种微量元素为主,主要富集在40℃~60℃的地热水之中.该研究结果对江苏省地热水长期研究及开发利用提供参考.