The coexistence of Cd(II) and tetrabromobisphenol A (TBBPA) in e-waste-impacted waters require remediation materials that remain stable during storage yet become highly reactive upon pollutant exposure. Here, we develop a silicate-stabilized ferrous sulfide (FeS-MS), in which Fe-O-Si interfacial bonding is suggested to contribute to enhanced structural and oxidative stability. More importantly, the silicate layer enables an ion-triggered activation mechanism, with Cd(II) acting as the most effective activator. Cd(II) is proposed to perturb Fe-O-Si interfacial bonding, thereby triggering interfacial activation that likely exposes reactive FeS domains and promotes Fe(II) release, while forming CdSiO3 and CdS via complexation and FeS substitution. This dual pathway enables ultrafast Cd(II) sequestration (up to 1292 mg/g) and shifts TBBPA behavior from limited adsorption (5.7%) to a coupled adsorption-reduction process, achieving concentration-dependent debromination (38% at 20 mu M and up to 68% at 10 mu M TBBPA). Common cations (Ca2+, Mg2+, Cu2+) also partially activate FeS-MS, supporting the generality of the interfacial activation concept. Across five representative water matrices, FeS-MS maintained near-complete Cd(II) removal and > 73% TBBPA removal over 14 days, while significantly reducing the toxicity of transformation products. These findings support a stability-reactivity interfacial switch governed by pollutant-induced disruption of Fe-O-Si bonding, offering a design principle for stable yet responsive reductive materials for multi-contaminant wastewater treatment.

Accurate fine-scale forest-type classification in mountainous regions is critical for ecological monitoring, forest resource assessment, and sustainable forest management. However, complex terrain and heterogeneous vegetation structures pose significant challenges to the accurate delineation of forest-type boundaries using conventional classification methods. In this study, we proposed a deep semantic segmentation framework that integrates a Swin Transformer encoder with a UPerNet decoder to improve fine-scale classification of forest types in mountainous regions. Gaofen-1 (GF-1) imagery with high spatial resolution (2 m) from the Dabie Mountains in China was used to train the model to distinguish four forest types: broadleaf forest, coniferous forest, mixed conifer–broadleaf forest (hereafter “mixed forest”), and sparse forest. Under three-fold leave-one-region-out cross-validation, the Swin Transformer–UPerNet model achieved a mean Intersection over Union (mIoU) of 83.17% ± 0.48%, a mean class accuracy (mAcc) of 90.74% ± 0.31%, and an overall accuracy (OA) of 93.72% ± 0.87%. The model outperformed U-Net, Swin-UNet, DeepLabV3+, SegFormer, and HRNet in overall classification performance. Independent validation in a separate region of the Dabie Mountains yielded an OA of 83.50% (95% CI: 81.20–85.70%), and cross-regional validation based on the pooled samples from three validation subregions in the Mount Huangshan region yielded an OA of 83.33% (95% CI: 78.75–87.50%). These results indicate that the integration of Transformer-based feature extraction and multi-scale feature fusion provides an effective approach for fine-scale forest-type mapping in mountainous regions. The resulting forest-type information can support forest resource inventories, ecological monitoring, and sustainable forest management.

Ever-increasing heat wave and frequent ambient ozone (O3) pollution in China has been exacerbating premature mortality. However, the urban-suburban-rural compound exposure inequity has seldom been explored. Here, a space-time-stratified case-crossover study of 1,040,125 all-cause deaths from 1390 townships in Anhui province, China, during 2013-2021 was conducted to comprehensively investigate the spatiotemporal variations in excess mortality attributed to compound exposure to both hazards and its driving factors along the UR (urban area)-MU (urban-dominated mixed region)-MR (rural-dominated mixed region)-RU (rural area) fourfold structure. Under various definitions, the odds ratios (ORs) of mortality associated with compound exposure to heat wave and O3 pollution ranged from 1.09 (95% CI, 1.06-1.12) to 1.28 (1.19-1.37) in UR; 1.13 (1.09-1.18) to 1.44 (1.32-1.56) in MU; 1.15 (1.13-1.16) to 1.50 (1.43-1.56) in MR; and 1.15 (1.12-1.18) to 1.69 (1.43-1.94) in RU. Correspondingly, the estimated excess mortality rates per 100,000 people ranged from 0.06 (95% CI, 0.04-0.07) to 0.38 (0.25-0.50) in UR; 0.05 (0.04-0.07) to 0.56 (0.37-0.76) in MU; 0.05 (0.04-0.06) to 0.87 (0.78-0.96) in MR; and 0.04 (0.02-0.05) to 0.89 (0.69-1.08) in RU. Notably, the excess mortality attributed to exposure to concurrent heat wave and O3 pollution was found to exhibit significant gradient variations across the UR-MU-MR-RU spatial structure. Overall, increased exposure to compound days (83.03%), rising baseline mortality (10.25%), and population aging (6.65%) were the primary drivers for the increase of attributable deaths. However, along the UR-MU-MR-RU gradient, the contribution of exposure to excess mortality decreased from 86.72% to 79.9%, while baseline mortality contributions increased from 5.4% to 13.42%, highlighting the roots of structural vulnerability in marginalized communities facing compound climate hazards. These findings support the spatially targeted measures for urban, suburban, and rural areas to better protect populations from increasingly prevalent compound climate hazards.

Fulvic acid (FA), a highly reactive and soluble fraction of dissolved organic matter in cultivated soils, facilitates the formation of stable colloids through complexation with iron (Fe), thereby significantly modulating the environmental mobility of arsenic (As). However, the migration behavior of As associated with FA-Fe colloids in porous media remains insufficiently characterized, particularly regarding the integration of coupled migration processes with quantitative modeling. This study investigated colloid-mediated As(III) migration in saturated porous media using column experiments and a time-fractional advection-dispersion equation (fADE). Increasing FA concentration enhanced As mobility, as evidenced by elevated breakthrough ratios and an increase in the fractional order α from 0.475 to 0.881, signifying the attenuation of memory effects and a transition toward Fickian migration. Conversely, elevated Fe concentrations promoted colloidal aggregation and suppressed As migration, with α decreasing to 0.437, capturing non-Fickian behavior associated with particle retention and deposition. Mechanistically, FA stabilizes FA-Fe colloids through electrostatic repulsion and steric hinderance while competing for adsorption sites, whereas Fe induces aggregation and enhances pore-scale interception, leading to As sequestration via inner-sphere complexation with Fe-OH groups. Under alkaline conditions, surface charge effects strengthened electrostatic repulsion and promoted migration, while elevated ionic strength compressed the electrical double layer, facilitated deposition. These results demonstrate that As migration is governed by the coupling between colloidal stability and interfacial interactions, which is effectively quantified by fADE. These findings provide a theoretical framework for understanding As mobility in subsurface environments and offer critical insights for groundwater remediation strategies involving colloid-facilitated migration.

Understanding the molecular-scale heterogeneity of dissolved organic matter (DOM) in tea plantation soils is essential for explaining regional differences in tea quality and mitigating contaminant risks. However, systematic studies on the structural characteristics of DOM in tea garden soils at different molecular weight scales and its binding behavior with pollutants remain limited. In this study, the molecular weight fractionation, structural composition, and arsenic (As) binding behavior of DOM in iron-rich red soils from three premium tea-growing regions of Huangshan City, China, were comprehensively investigated. An integrated spectroscopic approach was employed to analyze soil samples from Huangshan Mao Feng (Region 1, HSMF), Keemun Black Tea (Region 2, QMHC) and Taiping Houkui (Region 3, TPHK) plantations. The results revealed that the soil DOM exhibited high aromaticity (average SUVA₂₅₄ > 4.34 L·mg-¹·m-1) and was predominantly of microbial origin (fluorescence index > 1.9). Distinct regional patterns emerged: Region 2 exhibited the highest aromaticity (SUVA₂₅₄ = 4.75 ± 3.99 L·mg-¹·m-1) and a pronounced microbial signature in low-molecular-weight DOM (LMW-DOM, FI = 1.89 ± 0.87). Region 1 was characterized by highly humified, high-molecular-weight DOM (HMW-DOM, HIX = 8.64 ± 3.57). In addition, Region 3 displayed stronger allochthonous inputs (SR = 1.13 ± 0.58). PARAFAC analysis revealed that protein-like substances accounted for approximately 60 % of the fluorescence intensity in Region 2's HMW-DOM, whereas humic-like components dominated in Region 1 and Region 3. Furthermore, two-dimensional correlation spectroscopy revealed distinct DOM-As binding sequences: humic acid-dominated in Region 1 (389 nm → 324 nm → 288 nm), protein-dominated in Region 2 (425 nm → 390 nm → 386 nm) and fulvic acid-dominated in Region 3 (370 nm → 410 nm → 280 nm). These findings demonstrate that the molecular composition of DOM, which is shaped by local agronomic practices, determines its environmental reactivity. This provides crucial insights for optimising the management of tea quality and controlling the mobility of contaminants.

Fulvic acid (FA), a highly reactive and soluble fraction of dissolved organic matter (DOM) in cultivated soils, can form stable colloids upon complexation with Fe, thereby markedly influencing arsenic (As) mobility. However, the co-transport processes and mechanisms of FA-Fe-As(III) ternary complexes in groundwater systems remain insufficiently understood. Moreover, a quantitative modeling framework describing their transport in porous media has yet to be fully established. This study investigated colloid-mediated As(III) transport in saturated porous media using column experiments and a time-fractional advection–dispersion equation (fADE). FA significantly enhanced As(III) mobility (breakthrough ratio C/C0 increased from 0.63 to 0.98) by stabilizing colloids and competing for adsorption sites. Conversely, elevated Fe(III) concentrations lowered the FA/Fe molar ratio, inducing aggregation and reducing As(III) breakthrough by ~40%. Spectroscopic characterization confirmed As(III) sequestration via inner-sphere complexation with Fe-OH sites on FA-regulated iron (oxyhydr)oxides. Numerical simulations revealed that increasing FA raised the fractional derivative α (0.4746 to 0.8814), signaling a shift toward Fickian transport due to attenuated memory effects. In contrast, high Fe concentrations reduced α to 0.4367, effectively reproducing the observed non-Fickian behavior associated with aggregation-deposition processes. Furthermore, alkaline conditions favored transport via electrostatic repulsion, whereas high ionic strength suppressed mobility. These findings elucidate the coupling of colloidal stability and interfacial interactions, providing critical insights for predicting colloid-facilitated contaminant transport in subsurface environments.

Understanding spatiotemporal patterns of ecosystem service balance (ESB) is crucial for restoring damaged ecosystems. Existing studies focus on ESB's current status, neglecting its dynamic changes and drivers in management strategies. This study proposed a framework to classify China's county-level ecological management zones using the balance between supply and demand of terrestrial ecosystems in China (2000-2020) and formulated tailored strategies based on key drivers. Using expert scoring matrices, ecosystem service supply (ESS), demand (ESD), and ESB were assessed. A four-quadrant model categorized zones, while random forest analysis identified drivers. The results indicated: (1) ESS and ESD showed significant spatiotemporal disparities, with China's ESS exceeding ESD overall but the gap widening; (2) Four management zones were mapped via static/dynamic ESB indices; (3) Ecological land ratio dominated ESB variation, while changes in ecological land and impervious surfaces drove Delta ESB shifts; (4) Critical turning points in ESB/Delta ESB aligned with driver changes, informing zone-specific strategies. Integrating these dynamics and drivers enhances precision in ecological management, offering actionable insights for balancing conservation and development. This approach addresses gaps in current research by linking ESB trends to policy design, aiding sustainable ecosystem governance.

Heat wave and ozone (O3) pollution events are increasingly co-occurring in the context of climate change, especially in China. However, the effects of compound exposure to both hazards on cause-specific cardiopulmonary mortality remain largely unclear. In this study, we conducted a space-time-stratified case-crossover study of 550,634 township-level cardiopulmonary deaths in Anhui Province, China, from 2013 to 2021 to systematically evaluate the associations of exposure to heat wave and O3 pollution with multi-cause cardiopulmonary mortality and quantify their interactive effects Under various definitions, the odds ratios (ORs) of cardiopulmonary mortality associated with heat wave-only events, O3 pollution-only events, and compound events exposure ranged from 1.15 (95 % CI: 1.14-1.16) to 1.39 (95 % CI: 1.37-1.41), 1.02 (95 % CI: 1.01-1.03) to 1.04 (95 % CI: 1.03-1.04), and 1.22 (95 % CI: 1.20-1.23) to 1.75 (95 % CI: 1.62-1.88), respectively. Notably, more significant synergistic effects of heat wave and O3 pollution exposure at lag 1 day were observed on mortality risk from hypertensive heart disease, ischemic heart disease, acute myocardial infarction, hemorrhagic stroke, and chronic obstructive pulmonary disease. Females, older adults, and residents living in rural-dominated mixed regions experienced higher compound exposures. During the study period, the estimated number of excess cardiopulmonary deaths attributable to compound events exposure under various definitions ranged from 243 (95 % CI: 201-285) to 3227 (95 % CI: 2974-3480). More than 90 % of these excess deaths occurred after 2017 and were primarily concentrated in densely populated northern and central-eastern townships. These findings underscore that coordinated governance of air pollution and climate change could maximize reductions in the cardiopulmonary mortality burden.

Ambient fine particulate matter (PM2.5) has been widely associated with pulmonary tuberculosis (PTB). However, less is known about the impact and temporal variations of specific PM2.5 components on PTB. In this study, we employed breakpoint regression and distributed lag nonlinear models (DLNM) to assess the temporal variations in the effects of long-term exposure to PM2.5 and its components, including sulfate (SO42-), nitrate (NO3-), ammonium (NH4+), organic matter (OM), and black carbon (BC) on the incidence of 14,816,329 PTB cases across 31 provinces in mainland China from 2004 to 2018. We also explored sources of heterogeneity through meta-regression. The study found that long-term exposures to PM2.5 components were linked to higher monthly PTB incidence. The cumulative relative risks (CRR and 95 % CI) were highest at 1.379 (95 % CI: 1.331-1.428) per interquartile range (IQR) increase in NH4+, followed by 1.361 (95 % CI: 1.314-1.409) for NO3-, 1.331 (95 % CI: 1.282-1.382) for SO42-, 1.130 (95 % CI: 1.091-1.171) for OM, and 1.126 (95 % CI: 1.084-1.170) for BC. Smear-positive pulmonary tuberculosis (SPPTB) showed greater susceptibility. This association varied significantly across different socioeconomic and healthcare levels. In regions with lower per capita disposable income, urbanization rate, and the number of medical technical personnel per 1000 persons, NO3-and NH4+ were associated with higher PTB incidence rates. Over time, the effect sizes per unit increase in PM2.5 components has significantly diminished, but the impact of NH4+, NO3-and SO42-on PTB remains substantial. This observation might be due to reductions in PM2.5 exposure levels and changes in socioeconomic status factors, such as advancements in the economy and healthcare systems. Our study highlights the temporal variations in the effects of different PM2.5 components on PTB incidence, identifies key harmful components contributing to PTB, and provides scientific evidence for the PTB prevention and control strategies targeting specific PM2.5 sources.

Optimal water resource allocation in agricultural irrigation districts constitutes a core strategy for achieving coordinated regional water–food–ecosystem development. However, current studies rarely integrate inter-basin water diversion projects into the allocation, and the prolonged operation of diversion systems fails to adequately consider their ecological impacts in the irrigation districts. This study incorporates inter-basin water diversion into supply–demand dynamics and considers its influence on groundwater table changes in terrestrial ecological targets. Inexact two-stage stochastic programming (ITSP) was applied for optimal water allocation to address uncertainties from fluctuations in future water availability and interval ambiguity in socioeconomic information. Taking the densely populated agricultural irrigation district of Huaibei as a case study, we established a multi-stakeholder allocation model, considering the Yangtze-to-Huai water diversion project, to maximize comprehensive benefits under multiple scenarios of water availability for the years of 2030 and 2040. The results demonstrate that the district will face escalating water scarcity risks, with demand–supply gaps widening when available water resources decrease. The water redistribution in the second stage reduces scarcity-induced losses, achieving maximum comprehensive benefits. The water diversion project enhances supply capacity and boosts economic gains. The project can also decrease the fluctuation range of the total benefits by 5 × 106 CNY (2030) and 3.4 × 107 CNY (2040), compared with the scenario without the project. From 2030 to 2040, limited water resources will progressively shift toward sectors with higher economic output per unit water, squeezing agricultural allocations. Therefore, for irrigation districts in developing countries, maintaining a minimum guaranteed rate of agricultural water proves critical to safeguarding food security.

Freshwater ecosystems play a critical role in sustaining biodiversity, but with increasing anthropogenic disturbances in recent years, issues such as water degradation and biotic community decline have become increasingly severe. Although existing research has explored the impact of water quality factors and land use on macroinvertebrate communities, the specific mechanisms by which human activities indirectly influence macroinvertebrate diversity by altering the aquatic environment are still underexplored. Therefore, this study, on the basis of land use, aquatic environmental, and macroinvertebrate survey data, employed a Partial Least Squares Path Model (PLS-SEM) to elucidate the mechanisms by which land use and water quality factors jointly drive changes in macroinvertebrate communities. Our results demonstrate that macroinvertebrate community structure varied significantly among disturbance levels, with biodiversity indices increasing progressively as disturbance intensity lessened. Specifically, pollution-tolerant taxa dominated in high disturbance areas, Bellamya and Alocinma were predominant in moderate disturbance areas, whereas sensitive species were dominant in low disturbance areas. Land use explained 11.1% of the variation in diversity, about 2.6 times that of water quality factors (4.3%), indicating clear differences in their driving effects on macroinvertebrate diversity, as shown by variance partitioning analysis (VPA). According to the PLS-SEM results, built-up land, as the main negative factor, exerted combined effects on diversity both directly and indirectly by causing water quality deterioration. Water quality factors exhibited spatially differentiated effects: ammonia nitrogen and total nitrogen strongly inhibited diversity in high and moderate disturbance areas, whereas in low disturbance areas, total hardness and water temperature emerged as the primary positive drivers. This study elucidates the dynamic response mechanisms of macroinvertebrate communities to changes in land use and water quality, offering new perspectives for freshwater ecosystem health assessments and biodiversity conservation.

In iron (Fe)-rich tea plantation environments, the composition and behaviour of dissolved organic matter (DOM) differ markedly from those observed in other land use systems. Despite its importance, research on DOM in tea plantation soils remains limited, particularly with regard to its role in the transport and transformation of heavy metals, component-specific interactions and the quantification of environmental thresholds. This study examined the composition and fluorescence characteristics of DOM in surface soils, and quantified its Fe-mediated interactions with arsenic (As) under real-world tea plantation conditions. The results revealed that soil DOM in these environments exhibits low humification, high bioavailability and a predominantly terrestrial origin. Five distinct DOM components were identified, falling into two categories: humic acid-like and protein-like substances. A significant negative correlation was observed between soil As and Fe concentrations. Notably, in soils with high Fe levels (33,000 mg/kg), the presence of DOM reduced As concentrations by up to 53.6 %. This reduction is attributed to the rich array of adsorption sites in DOM, which influence Fe redox processes by facilitating the reduction of As(V) and promoting the formation of insoluble Fe-As precipitates through complexation. These findings enhance our understanding of DOM composition in tea plantation soils and shed new light on the environmental interactions among DOM, Fe and As. Such insights are crucial for assessing As mobility, enhancing soil quality monitoring in tea-growing regions and promoting the sustainable growth of the tea industry.

The water–soil interface contains substantial amounts of dissolved organic matter (DOM) and iron minerals. However, the stability and aggregation behavior of DOM-Fe colloids under varying concentrations and mineral compositions remain unclear. Therefore, the binding behavior of these composite colloids with As(III) requires further investigation. This study analyzes the surface charge and particle size variations of the composite colloids to understand their stability and the binding process with As. Results indicate that the C/Fe molar ratio affects the dispersion of the three types of humic acid–iron (HA–Fe) composite colloids. As the C/Fe ratio increases, the Zeta potential of the composite colloids increases, and their particle size decreases, with a minimum size of 135, 232, and 188 nm. When the C/Fe molar ratio is below 4.7, sedimentation occurs, with the maximum sedimentation value (C/C0) reaching 0.7. As pH increases, the Zeta potential of all three HA–Fe composite colloids increases by 6.3, 8.1, and 6.2 mV respectively, and their particle sizes decrease, with average reductions of 336, 483, and 256 nm. The binding capacity with As(III) increases as the C/Fe ratio rises from 0 to 23.3. At a C/Fe ratio of 23.3, the binding coefficients (logKD) with As(III) are 2.42, 2.86, and 2.96 for the three composite colloids, respectively. Among them, the HA–FeO(OH) composite colloid shows the highest binding rate with arsenic at 92

Record-breaking heat wave and frequent ozone (O3) pollution events are causing greater harm to the Chinese population. However, the fine spatial variation of compound exposure risks from these two extreme events remains largely unknown in China. In this study, we employed a three-stage risk assessment framework to reveal the heterogeneity in mortality risk associated with compound exposures to heat wave and O3 pollution in Anhui Province (2013-2021) at the township-level. We found a significant synergistic effect between heat wave and O3 pollution on daily mortality at the province level, with the relative excess odds due to interaction (REOI) gradually increasing from 0.01 to 0.21 as increasingly stringent thresholds for definingheat wave and O3 pollutionevents were applied. Nevertheless, spatial heterogeneity in such synergistic effects was observed across townships. A higher proportion of elderly and agricultural populations, lower educational attainment, lower hospital accessibility, lower green space coverage, and poorer air quality within a township drove stronger synergistic effects. Notably, the REOIs systematically increased after incorporating spatial information corrections, indicating that neglecting spatial effects might underestimate the health risks of compound hazards. Our findings provide valuable insights for grassroots units in developing countries to effectively address compound climate hazards and optimize resource allocation.

Dissolved organic matter (DOM) serves as a critical link in the migration and transformation of heavy metals at the soil–solid interface, influencing the migration behaviour and transformation processes of Cu2+ in soil. There have been studies on the combination mechanisms between DOM and Cu2+ in paddy soils. However, the adsorption/complexation and redox processes between DOM and Cu2+ in other agricultural soil types (such as dry farmland and vegetable fields) are unclear. In order to reveal the combination process of DOM with Cu in different agricultural soil types and the dynamic changes in chemical behaviour that occur, this study analysed the variability of DOM components and structure in three soils using three-dimensional fluorescence spectroscopy and X-ray photoelectron spectroscopy. In addition, the priority order of different DOM compounds in combination with Cu and the change process in relation to the Cu valence state in the soil of Lujiang County, Anhui Province, was revealed based on laboratory experiments. The results showed that the composition of soil DOM was mainly composed of humic-like and fulvic-like substances with a clear terrestrial origin and that the organic matter showed a high degree of decomposition characteristics. The results indicated that the composition of soil DOM is mainly composed of humic and fulvic acid-like substances, and they have obvious characteristics of terrestrial origin. In addition, the soil organic matter showed high decomposition characteristics. The complex stability constants (lgKM) of humic acid-like substances with Cu2+ follow the order of forest land (lgKM = 5.21), vegetable land (lgKM = 4.90), and dry farmland (lgKM = 4.88). The lgKM of fulvic acid-like substances with Cu2+ is in the order of dry farmland (lgKM = 4.51) and vegetable land (lgKM = 4.39). Humic acid-like substances in soil DOM combine preferentially with Cu2+, showing a stronger chelating affinity than fulvic acid-like substances. Cu2+ complexes mainly include hydroxyl, phenolic hydroxyl and amino functional groups are included in soil DOM, accompanied by redox reactions. In comparison to dry farmland, the soil DOM in forest and vegetable fields undergoes more intense redox reactions simultaneously with the chelation of Cu2+. Therefore, the application of organic fertilisers to vegetable and forest soils may lead to uncertainties concerning the fate of heavy metals with variable chemical valence. These results contribute to a deeper understanding of the interaction mechanisms between DOM and Cu2+ in agricultural soils.

Dissolved organic matter (DOM) is widely present in soil environments and plays a crucial role in controlling the morphology, environmental behavior, and hazards of arsenic (As) in soil. In the Fe-rich red soil of tea plantations, the decomposition of tea tree litter complicates DOM properties, leading to more uncertain interactions between DOM, Fe, and As. This study focused on three tea plantations in Huangshan City to investigate the contents of DOM, Fe, and As in surface red soils (Ferralsols) and establish their correlations. Three-dimensional fluorescence spectroscopy and PARAFAC analysis methods were used to analyze the DOM components and fluorescence signatures. Additionally, the process and mechanism of the binding of DOM-Fe with As were explored through laboratory experiments on the morphological transformation of As by DOM-Fe. The results showed that the pH values of the soils in the three tea plantations ranged from 3.9 to 5.2, and the entire sample was strongly acidic. The DOM exhibited strong intrinsic properties and low humification, containing three types of humic acid components and one intermediate protein component. The DOC content in the Fe-rich red soil did not have a direct correlation with Fe and As, but the interaction of DOM fractions with Fe significantly influenced the As content. Specifically, the interaction of protein-like fractions with Fe had a more pronounced effect on the As content. The maximum sorption rate of As by DOM was 15.45%, and this rate increased by 49 to 75% with the participation of Fe. In the configuration of the metal electron bridge, Fe acts as a cation, forming a connecting channel between the negatively charged DOM and As, thus enhancing the DOM’s binding capacity to As. DOM-Fe compounds bind As through surface pores and functional groups. These findings provide deeper insights into the influence of DOM on As behavior in Fe-rich soil environments and offer theoretical support for controlling As pollution in red soil.

Southwestern China is a critical biodiversity hotspot area, and many large hydroelectric projects have been established in the valleys in the region. Tree growth in the valleys will be affected by both regional climate and reservoir impoundment. However, it remains unknown whether the radial growth of trees in the valleys has a common response pattern to the regional climate, and it is also unclear whether the response of radial growth to reservoir impoundment can be detected. In this study, we developed tree-ring width chronologies of Pinus yunnanensis Franch. collected at 11 sites with vertical and horizontal gradients to three hydroelectric reservoirs in three riverine valleys in southwestern China. We analyzed the radial growth responses to the regional climate from 1986 to 2017 by correlation with instrumental meteorological data. Tree growth responses to reservoir impoundment were investigated through spatial and temporal comparisons using the change in the Euclidean distance and difference test. We also distinguished their responses at tree-ring sites without influenced by reservoir impoundment including two sites in the valleys and seven sites at high elevations. The results showed that the climate conditions in May and the dry season before the growth season significantly limit the radial growth in the valleys, which is different to that at high-elevation areas in southwestern China. Growth variations in the valleys are related to elevations and the trees in similar slopes positions exhibit similar responses. For trees in the low slope positions, both variance and mean values of radial growth are affected by reservoir impoundment. Trees at relatively low sites (i.e., sites M2, R2, L2), rather than the trees close to the reservoirs (i.e., sites M1, R1, L1), respond more sensitively to reservoir impoundment.

Metal contamination in surface water is one of the major environmental risk factors contributing to the incidence and mortality of gastric cancer (GC) in rural China. In this study, the generalized additive model (GAM) was used to explore the single and interactive effects of metal elements in surface water on GC incidence on the watershed scale in Lujiang County, east of China. Spatially, the areas with a high incidence of GC were concentrated in the northwest watershed where the drainage system was relatively developed. Apart from Sr, the average concentrations of Al, As, Be, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, and Zn in the northern watershed were higher than those in the southern watershed. Among them, the average concentrations of Be (0.036 mg/L), Fe (1.539 mg/L), Mn (0.355 mg/L), and Ni (0.040 mg/L) well exceeded China's Grade III water quality standards. On the sub-watershed scale Be (F(5.130)), Pb (F(4.963)), As (F(3.508)), Cu (F(3.023)), Zn (F(2.922)), Cr (F(2.725)), Sn (F(2.588)), and Co (F(2.140)) in surface water were the main elements contributing to the high incidence of GC in Lujiang County, and the interaction effect mostly showed nonlinear enhancement. Especially, the nonlinear enhancement effect of Be with Cu (F(7.051)), Co (F(5.798)), Sn (F(5.328)), and Pb (F(5.193)) was more significant and had a greater effect on the incidence of GC. This study provides compelling direct evidence on the effects of metal contamination in surface water on the higher GC incidence in Lujiang County, China. It is recommended that there be routine monitoring of metal concentrations in surface water resources.

Understanding the response of the mechanisms driving ecosystem services (ESs) to socioecological factors is imperative for regional sustainable ecosystem management. However, previous studies of the mechanisms driving ESs have focused more on the degree and direction (positive and negative) of effects on ES supply or the supply–demand balance, while their nonlinear response processes have not been fully considered. In this study, a theoretical framework was developed through integrating land use/land cover data and supply and demand matrices with random forest models to assess response processes, including the relative importance and marginal effects, of essential factors that drive ES demand, supply, and supply–demand balance. Using the Yangtze River Economic Belt (YREB) as an example, our results indicated that the ES deficit regions (332 of 1070 counties or 14.45% of the area) of the YREB were located mainly in the three national urban agglomerations. Moreover, this study indicated that natural environmental factors (such as slope and precipitation) significantly influence the supply and supply–demand balance of ESs, while socioeconomic factors (such as cropland ratios and population density) profoundly influence the demand for ESs. However, cropland ratios were the most important drivers of ES supply, demand, and supply–demand balance in the YREB. Moreover, three types of response processes were identified in this study: logarithmic increase, logarithmic decrease, and volatility increase. Specific driving factors (e.g., proportion of cropland area, precipitation, population density, and slope) had significant threshold effects on the supply–demand balance of ESs. The turning points that can be extracted from these response processes should be recommended for ecosystem restoration projects to maintain regional sustainable ecosystem management.

The phenomenon of algal blooms resulting from lake eutrophication has the potential to increase the concentration of dissolved organic matter (DOM) and consequently influence the environmental behaviour of arsenic (As). In the subtropical region, the interplay between DOM, Fe/Mn and As becomes complex as Fe/Mn-rich substances from soils and sediments enter eutrophic lakes. The mechanisms by which DOM-Fe/Mn interactions affect the transformation of As species remain uncertain. Therefore, the Chaohu Lake Basin was selected as a representative case study site to investigate the levels of DOM, As, Fe and Mn in the water and to establish their associations. In addition, the interaction mechanism between DOM-Fe/Mn and As was investigated by elucidating the transformation behaviour of DOM-Fe/Mn on As species in a controlled laboratory environment. The results showed that in cases where the coexistence of Fe and Mn concentrations was relatively low (e.g. Fe < ∼0.5 mg/L and Mn < ∼0.6 mg/L), the concentration of As in water would increase proportionally with the simultaneous increase of both Fe and Mn concentrations (As < 5 μg/L). However, when the concentration of either Fe or Mn reached 10 mg/L, the proportion of As complexed by DOM increased significantly, reaching 99.73% and 99.66%, respectively. In the configuration of a metallic bridge, the elements Fe and Mn act as connectors between negatively charged DOM and As, thereby increasing the adsorption capacity of DOM for As. The alcohol and alkene functional groups present on the DOM-Fe/Mn surface show a preference for binding with free species of As in aqueous environments. In addition, the reductive groups on the surface of DOM not only directly convert As(V) to As(III), but also facilitate the reduction of Fe(III) to Fe(II), resulting in the indirect conversion of As(V) to As(III). Thus, this study provides a comprehensive understanding of the transport and transformation processes of arsenic in subtropical eutrophic lakes.