Strong and selective metal chelating ligands are important for harnessing metal properties as well as for their selective sensing and detection. In the current study we synthesized a novel pyridine-based hydrazone (L) that showed strong and selective complexation with Cu2+. The chelation properties of L were studied in detail by different analytical methods, and the complex formed (L-Cu) was characterized in solid state by single crystal Xray analysis. This strong chelation property of L with Cu2+ was further utilized in the selective naked-eye/ colorimetric and spectroscopic determination of Cu2+ in acetonitrile/HEPES buffer (20 mM pH 7.2) (1:1) mixture and applied in real time environmental samples. By the addition of Cu2+ into the solution of L a fast color change to yellow was observed. L showed 100% selectivity for Cu2+ in the presence of other competing metal ions. The 1:1 complex formation between L and Cu2+ was confirmed by Job's plot showing similarity to the complex characterization data of HR-ESI MS and single crystal X-ray structure analysis. The limit of detection (LOD) was calculated as low as 7.63 nanomolar, that was found below the WHO permitted level (20 mu M). This chelation phenomenon was reversible; L was recovered by the addition of EDTANa2. A paper strip method was also devised for the instant detection of Cu2+ in water. It was utilized in environmental water samples for Cu2+ detection that showed excellent recovery. All these results concluded that L is a strong Cu2+ chelating ligand that could be used for the synthesis of Cu2+ complexes as well as in chromogenic or naked-eye and spectroscopic sensing and quantification of Cu2+.

The alpine grassland vegetation on the Qinghai-Tibet Plateau is composed of plant patches in varied sizes. It remains uncertain whether vegetation recovery following grazing exclusion (GE) in degraded grasslands is driven by increases in patches number (NP), patch size (PS), or both. We based our predictions on two hypotheses: GE intensifies plant competition, and facilitation prevails near patches while competition prevails in interpatch spaces. We predicted that the NP would remain stable or decrease and PS would increase under GE treatment. To evaluate these predictions, we conducted a study in six lightly degraded alpine grasslands under free grazing (FG) conditions in Bangor County, Tibet Autonomous Region, China, with corresponding GE treatments using transects in 2017 and 2018. Results revealed that four sites in 2017 and five sites in 2018 had reduced NP and increased PS, with probabilities of 0.033 (2017) and 0.004 (2018), respectively, and a joint probability of 0.0001 under the null hypothesis that GE does not affect NP or PS. The NP reduction was solely due to the decrease in small patch sizes. An increase in PS was common across species, and a predominant tendency for NP reduction was observed among species across the sites. The overall changes in NP and PS were primarily driven by the three most abundant species (contributing more than 60% in both years), rather than by shifts in floristic composition. Our findings highlight that vegetation recovery in Bangor alpine steppes following GE relies solely on the expansion of existing patches rather than the recruitment of new ones in interpatch gaps. We recommend prioritizing growth-promoting measures, such as nutrient or water management, over seed addition when assisting with GE for restoring lightly degraded grasslands.

As critical transitional zones between land and sea, estuaries are confronting the dual threats of increasing acidification and hypoxia driven by human activities and climate change. However, the combined effects of these stressors on estuarine nitrogen removal processes remain poorly understood. In this study, using stable-isotope tracing and molecular techniques in the Yangtze estuary, we found that hypoxia promoted N removal, yet concurrent acidification can override this effect, leading to net inhibition and a consequent reduction in estuarine nitrogen removal capacity. However, in seasonally hypoxic zones, these combined stressors generally enhanced nitrogen removal rates (by up to 34.4%), which suggests a degree of resilience under such perturbations. Nevertheless, the concurrent acidification-hypoxia in seasonally hypoxic areas stimulated N2O emissions (8.5-44.4%), which may intensify climate forcing and thereby further exacerbate these environmental stressors. Metagenomic and quantitative PCR analyses corroborated these response patterns, revealing coordinated changes in the abundance and expression of key nitrogen-removal genes, as well as divergent microbial response strategies and niche differentiation under acidification-hypoxia stress. This study elucidates the previously overlooked interactive effects of acidification and hypoxia on estuarine nitrogen removal, providing a mechanistic basis for refining biogeochemical models to improve the reliability of simulations under multiple stressors.

Globally, rivers can yield a large amount of nitrous oxide (N2O) by microbial nitrogen processes. However, how the nitrification mediated N2O production in river sediments remains poorly understood. Here, we investigated potential nitrification and N2O production rates, and ammonia-oxidizing bacteria (AOB) communities in the mainstream and eight major tributaries of the Yangtze River. Potential nitrification and N2O production rates varied significantly, which were both significantly lower in the middle reach than in the upper and lower reaches. Potential nitrification and N2O production rates also varied significantly across the tributaries, in which Wujiang and Hanjiang showed higher rates. Nitrification dominated N2O production in the upper reach, whereas denitrification was mainly responsible for N2O production in the middle and lower reaches. Moreover, denitrification was the dominant pathway for N2O production in the tributaries (except for Ganjiang). AOB diversity varied significantly across the upper, middle and lower reaches. Microbial complexity and stability of AOB were significantly higher in the lower reach than the middle and upper reaches. Sediment size, NH4+, Fe(II), and DOC significantly correlated with AOB abundance, potential nitrification, and N2O production. These results suggest that sediment characteristics greatly affect N2O production by modifying nitrogen availability and microbial processes. In addition, enhanced nutrient availability can increase microbial complexity and further facilitate nitrification activity and N2O production, representing a positive climate warming feedback loop.

Estuaries worldwide are experiencing intensifying acidification and hypoxia, driven synergistically by anthropogenic activities and global climate change. Nevertheless, their combined impact on the emissions of the potent greenhouse gas methane (CH4) and its underlying regulatory mechanisms remains poorly understood, undermining our ability to project climate feedbacks. Here, we integrated 13C stable isotope tracing, DNA/mRNA-based qPCR, and amplicon/metagenomic sequencing to unravel how acidification-hypoxia interactions regulate the complex balance between CH4 production and consumption in estuarine sediments. Results showed that aquatic acidification and hypoxia combined to significantly increase CH4 emissions from estuarine sediments (P < 0.05), in a non-additive (antagonistic) manner where oxygen availability was the dominant factor governing this response. Notably, acidification increased CH4 emissions by suppressing methanotrophy more strongly than methanogenesis, whereas hypoxia preferentially stimulated methanogenic activity over CH4 oxidation. These response patterns were further demonstrated by metagenomic sequencing and mRNA-based quantitative PCR analyses, which revealed coordinated shifts in both the relative abundance and transcriptional activity of key functional genes. These findings uncover a previously overlooked mechanism whereby the worldwide co-occurrence of acidification and hypoxia in estuarine ecosystems jointly promote CH4 emissions, providing a scientific basis for improving predictive models of the global CH4 cycle and its climate feedbacks under combined anthropogenic and climatic stressors.

Antibiotic resistance gene (ARG) monitoring in environmental systems increasingly relies on DNA-based molecular approaches; however, the extent to which DNA extraction strategies bias downstream resistome interpretation remains insufficiently understood. This study systematically evaluated the effects of single versus successive DNA extraction on DNA recovery, microbial community composition, and the abundance and diversity of 385 genes related to antibiotic resistance including ARGs and mobile genetic elements (MGEs) across three contrasting matrices: water, sediment, and fish intestinal tissue. Successive extraction markedly increased DNA yield and detection of functional genes in water and sediment, particularly for low-abundance and particle-associated taxa. Enhanced recovery resulted in higher richness and abundance of ARGs and MGEs and strengthened correlations between intI1, ARGs, and bacterial taxa, indicating that single-cycle extraction may underestimate resistome magnitude and potential host associations in complex matrices. Conversely, fish intestinal tissue, used here as a representative biological matrix, showed limited benefit or even reduced gene abundance with repeated extraction, likely due to rapid depletion of extractable nucleic acids and DNA degradation. While successive extraction improves recovery efficiency, the potential inclusion of extracellular or relic DNA suggests caution in interpreting inflated ARG abundance. Overall, our findings demonstrate that DNA extraction is a matrix-dependent methodological driver that can reshape both quantitative outcomes and ecological inference. Matrix-specific optimization and careful protocol selection are therefore essential for improving data comparability and minimizing methodological underestimation in environmental resistome assessments.

Industrial legacy sites, even after ceasing operations, often suffer from severe heavy metal contamination in soils. These residual pollutants can pose significant threats to the surrounding environment. However, tracing the sources, migration pathways of heavy metals from such sites, and their impacts on adjacent environments remains a major challenge. The present study focuses on historical mercury (Hg) contamination at two decommissioned industrial sites (an e-waste dismantling site and a pyrite smelting site), and employed Hg isotope analysis to investigate the sources, pollution pathways, subsurface migration in soils, and uptake of Hg by leafy vegetables. Topsoils at both sites showed substantially elevated Hg concentrations (2.5-32.1 mg kg(-1)), primarily derived from direct waste discharges during production. At the e-waste dismantling site, direct Hg emission from industrial waste gas was the primary contributor to adjacent soil contamination, while gaseous elemental Hg re-emitted from legacy-contaminated soils served as the dominant Hg source for nearby vegetables. Soil organic matter was identified as the key factor driving subsurface Hg accumulation at this site. In contrast, the pyrite smelting site exhibited a different contamination mechanism: acidic wastewater leaching altered soil pH, and under low pH conditions, strongly bound Hg was remobilized, leading to Hg pollution in deeper soil layers (down to similar to 500 cm depth). These findings reveal distinct environmental risks from direct emission and legacy Hg re-emission across different types of abandoned industrial sites, highlighting the need for site-specific management and remediation strategies to mitigate soil and agricultural Hg contamination.

Reservoirs in karst regions, which supply drinking water for around a quarter of the global population, exhibit complex pollutant heterogeneity due to fracture-conduit hydrogeology and seasonal hydrological rhythms. This year-long study investigated a subtropical monsoon climate karst reservoir, examining the spatiotemporal dynamics of dissolved organic matter (DOM), heavy metals, pesticides, and antibiotics. The formation potentials of seven major classes of disinfection by-products (DBPs) were quantified, and correlation analysis and partial least squares regression (PLSR) models were used to identify key precursors and drivers. The results showed that seasonal wet-dry alternation was the dominant mechanism which governed pollutant heterogeneity, and DOM was identified as the universal dominant precursor of all DBP categories, with both terrestrial organic matter and autochthonous tyrosine-like substances contributing significantly. Nitrogen-containing pesticides and quinolone antibiotics promoted the generation of specific DBPs, whereas the presence of manganese inhibited DBP formation, likely through both precursor oxidation and interference with chlorination. Moreover, PLSR models showed excellent predictive performance for the formation of the various classes of DBPs. However, conventional drinking water treatments (coagulation, sedimentation, sand filtration) proved inadequate in preventing potentially hazardous DBP levels upon chlorination, and it is recommended that both pre-and post-oxidation as well as activated carbon treatments are used to ensure the safety of drinking water produced from such reservoirs. Overall, this study provides valuable scientific background for control of drinking water safety in sub-tropical karst regions.

Based on six periods of remote sensing image data of land resource utilization from 1995 to 2020, this study conducted an analysis of the carbon balance of land resource utilization in the Beijing-Tianjin-Hebei region of China and proposed spatial optimization strategies for land resource utilization. The results were as follows: (1) Over the 25-year period, the carbon emissions from land use in the Beijing-Tianjin-Hebei region showed a significant "inverted U-shaped" curve pattern. Construction land was the main carbon source, and the spatial distribution presented a "core-edge" gradient emission pattern, with the highest carbon emission intensity in the core area of Beijing-Tianjin-Tangshan, followed by the central area of Jizhongnan, and the ecological area of Jibei maintaining a low-carbon level. (2) Although the total carbon absorption showed a slow growth trend, the regional carbon deficit situation continued to intensify, reflecting the ecological imbalance problem during the rapid urbanization process. (3) Based on the carbon neutrality goal and the main functional zoning, the study optimized and restructured the territorial spatial divisions of the Beijing-Tianjin-Hebei region into six categories, namely, low-carbon maintenance-agricultural product main production area; carbon intensity control-optimized development zone; carbon sink function-key ecological function area; carbon sink function-key development zone; high-carbon optimization-optimized development zone; and high-carbon optimization-key development zone. Resource allocation plans are suggested for each optimized zone, serving as a scientific basis for the coordinated development of the Beijing-Tianjin-Hebei region of China via low-carbon transformation and territorial spatial optimization configuration.

As an emerging contaminant, the environmental fate of palladium (Pd) in estuaries depends critically on dissolved organic matter (DOM), yet its binding mechanisms in tropical systems remain unclear. We characterized sedimentary DOM and its complexation with Pd across Hainan Island estuaries. Multiple techniques were employed: ultraviolet-visible spectroscopy (SUA254, A253/A203), excitation-emission matrix fluorescence with parallel factor analysis (EEM-PARAFAC), and fluorescence quenching titration. Sedimentary DOM exhibited low molecular weight and low humification, with enrichment of tryptophan-like proteins and microbial metabolites. A distinct land-sea gradient showed declining terrestrial inputs and increasing marine microbial sources offshore. Humic-like and fulvic-like components occurred only in southeastern estuaries. Crucially, DOM composition controlled Pd complexation strength and migration risk. In eastern and southern estuaries, macromolecular components provided strong complexation (>50%), effectively sequestering Pd. This yielded lower migration risks (36-48%). In contrast, western estuaries were dominated by low-molecular-weight fractions, which showed weak complexation (<20%) and enhanced Pd mobility, resulting in a 61% migration risk. Unlike highly humified temperate estuaries such as the Yangtze River Estuary and Chesapeake Bay-where HIX values frequently exceed 10 and DOM is dominated by terrestrial humic substances-the weaker complexation capacity of tropical DOM leads to higher Pd mobility. This highlights the unique environmental vulnerability of tropical island estuaries to emerging metal contaminants. Our findings establish that spatial heterogeneity in DOM composition critically controls Pd migration risk, providing a theoretical framework for predicting the environmental behavior of platinum-group elements (PGEs) in analogous tropical coastal environments globally.

Plant-plant interactions play a pivotal role in shaping community structure and regulating nutrient cycling through modulating both intra- and interspecific resource allocation. These interactions largely impact ecosystem services, particularly in the context of global climate change. To address this, our review synthesizes global research on plant-plant interactions, evaluates current progress, and identifies key knowledge gaps to guide future research. We analyzed 346 peer-reviewed articles from the Web of Science to quantify intra- and interspecific interactions. Research trends were evaluated based on spatial and temporal patterns, plant functional groups, plant organs of focus (e.g., roots, leaves), and environmental drivers (e.g., atmospheric, soil, and biological factors). This systematic evaluation highlights key research priorities and biases. Research efforts are geographically concentrated in China and the United States, with a strong focus on grasslands. Taxonomically, Poaceae, Leguminosae, and Asteraceae are disproportionately represented. Despite the substantial body of research, significant geographical and ecosystem biases persist, with ecosystems like tropical, alpine, and desert regions being underrepresented. Aboveground interactions and environmental factors such as light intensity and soil moisture around trees, as well as rhizosphere soil nutrients in grasslands and crops, dominate the focus of studies. However, the essential roles of roots and the rhizosphere in nutrient uptake, water transport, and microbial interactions remain underexplored. It is crucial for ecological research to broaden the scope by incorporating a wider range of ecological factors, exploring underexplored ecosystems, and achieving a more balanced focus on both aboveground and belowground dynamics. To advance ecological theory and application, future research must adopt a more holistic framework that integrates underrepresented ecosystems (e.g., tropical, alpine, desert) and balances the study of above- and belowground dynamics. Expanding research to include root-rhizosphere interactions, microbial symbioses, and multifactorial environmental drivers (e.g., temperature gradients, CO2 levels, biotic stressors) will enhance the predictive capacity for ecosystem responses to global change. Bridging these knowledge gaps will not only enhance our understanding of plant ecology but also inform better conservation strategies and ecosystem management practices in the face of ongoing environmental changes.

Seafood consumption is not only deeply embedded in dietary structures but also serves as a key pathway for human dietary exposure to per- and polyfluoroalkyl substances (PFASs). However, probabilistic dietary risks in high seafood consumption regions remain unclear. This research presents PFASs occurrence, bioaccumulation, and trophodynamics in the East China Sea (ECS), and evaluates age-group specific dietary exposure in the Yangtze River Delta Urban Agglomeration (YRDUA). PFASs were ubiquitous in seawater and organisms, with cephalopods and shrimp showing the higher concentrations. The perfluorooctane sulfonate (PFOS) replacement, 6:2 chlorinated polyfluoroalkyl ether sulfonate (6:2Cl-PFESA), and its precursor perfluorooctane sulfonamide (PFOSA) exhibited biomagnification potentials comparable to those of legacy long-chain PFASs, challenging the assumption that PFASs alternatives are safer. Risk quotient analysis further indicated that 6:2Cl-PFESA and some long-chain PFASs, such as perfluorotridecanoic acid (PFTrDA), perfluorodecanoic acid (PFDA) posed higher ecological risks to invertebrates than to fish. Monte Carlo based risk mapping revealed substantial heterogeneity across age groups and a clear north-south geographic gradient within the YRDUA, with children aged 2 to 6 years in northern cities and adults in southern cities exhibiting the higher exposure levels. These findings offer a scientific basis for targeted exposure management and policy intervention.

Myriads of organic contaminants in atmospheric fine particulate matter (PM2.5) have been documented to pose appreciable health risks. Meanwhile, the quantities of analytes monitored by most established approaches have remained modest, hindering systematic elucidations of PM2.5-bound pollution. Therefore, this study developed a high-throughput and efficient methodology for targeted determination of 625 trace-level chemicals, which covered both emerging and conventional contaminants, as well as their transformation products. Additionally to notorious pollutants, like legacy brominated flame retardants (LBFRs), polycyclic aromatic hydrocarbons, organochlorine pesticides, and phthalate esters (PAEs), our analyte list also encompassed multiple classes of contaminants of emerging concern, including alternative BFRs, synthetic antioxidants, organophosphate esters (OPEs), liquid crystal monomers, and PAE replacements (PAEAs). The optimized protocol demonstrated satisfactory recoveries and negligible matrix effects for over 96% of the target compounds. The resulting method detection limits, ranging from 0.011 to 5.47 pg/m3, could rival the values reported for counterpart protocols quantitating even less contaminant categories. Following the final analytical procedures, we confirmed the measurable levels of 337 analytes in Chinese urban PM2.5 samples, with total concentrations spanning from 15.5 to 76.0 ng/m3. It is noteworthy that compound groups of the greatest abundances were PAEAs and OPEs, both introduced as alternative plasticizers and/or flame retardants, indicating recent market shifts of industrial additives in China. Moreover, outstanding residues were also observed for tire-derived chemicals, suggestive of their urban signatures. The broad-spectrum surveillance approach we built can facilitate data acquisitions for comprehensive regulation of atmospheric pollution.

Urban groundwater is increasingly recognized as an emerging reservoir and transport pathway for antibiotics, antibiotic-resistant bacteria (ARB), and antibiotic resistance genes (ARGs), posing potential ecological and public-health risks. However, the distribution and transport mechanisms of antibiotics and ARGs in groundwater systems under complex anthropogenic pollution remain insufficiently understood. Here, we investigated groundwater in Shanghai’s Taopu Industrial Park, a region characterized by multiple industrial contamination sources. Antibiotic concentrations were quantified using ultra-performance liquid chromatography–tandem mass spectrometry, while metagenomic sequencing and high-throughput quantitative PCR were employed to characterize ARG diversity and abundance and microbial community composition. Integrated analyses were performed to elucidate the distribution and transport patterns of antibiotics, microorganisms, and ARGs, and to identify key environmental drivers. Co-occurrence network analysis was further applied to infer potential ARB hosts. Twenty antibiotics were detected in groundwater at concentrations ranging from 24.1 to 1161.1 ng L-1, with sulfonamides dominating. Fluoroquinolones were more enriched in soil than groundwater, likely due to stronger sorption associated with their polar/ionic functional groups, whereas tetracyclines exhibited higher vertical mobility than sulfonamides. Antibiotic concentrations decreased exponentially with depth. Groundwater physicochemical parameters (dissolved organic carbon, salinity, dissolved oxygen, and conductivity) together with co-occurring polycyclic aromatic hydrocarbons (PAHs) were the major determinants of antibiotic distribution. Groundwater microbial communities were bacteria-dominated and of relatively low diversity, with Proteobacteria, Bacteroidetes, Actinobacteria, and Firmicutes as the major phyla. Actinobacteria occurred at higher relative abundance than in other industrial groundwater systems, likely reflecting selective pressure from the combined presence of antibiotics and PAHs, consistent with their roles in PAH degradation, antibiotic production, and ARG hosting. Redundancy analysis indicated that contaminants—particularly antibiotics and PAHs—were the primary drivers of microbial community structure, exceeding the effects of physicochemical parameters (pH, dissolved organic carbon, and dissolved oxygen). The composition and relative abundance of 21 ARG types were highly similar between soil and groundwater, with multidrug, macrolide, glycopeptide, tetracycline, and peptide resistance genes predominating in both media, suggesting potential ARG exchange and migration across compartments. In groundwater, contaminants (especially antibiotics and PAHs) were the dominant determinants of ARG profiles, followed by microbial community composition, while mobile genetic elements and physicochemical conditions further facilitated ARG dissemination. Network analysis identified several shared potential ARG-hosting genera in soil and groundwater, indicating that ARB-mediated vertical transport may represent an important pathway for ARG contamination in groundwater. Overall, this study reveals the coupled occurrence, transport behavior, and environmental drivers of antibiotics, microbial communities, and ARGs in urban groundwater under anthropogenic influence. The findings highlight the need for integrated management strategies that reduce source pollutants and selective pressure to mitigate ARG dissemination in subsurface environments.

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are highly toxic, persistent organic pollutants that bioaccumulate through food webs and constitute a major human exposure pathway. National-scale dietary exposure assessments in China remain uncertain due to limited monitoring data, assumptions of complete bioaccessibility, and heterogeneity in regional emissions and dietary patterns. In this study, we developed a China-specific multimedia food-chain model to quantify environmental transfer, food-chain accumulation, and human exposure of PCDD/Fs across six major urban agglomerations, including the Beijing-Tianjin-Hebei (BTH), Yangtze River Delta (YRD), and Pearl River Delta (PRD). The model integrates regional environmental concentrations, population dietary patterns, and cooking-related bioaccessibility for more accurate exposure estimation. Model predictions agree well with observations (n = 224), with 87.9% of mass concentrations and 91.5% of toxic equivalents (TEQs) within one order of magnitude, and significant correlations (r = 0.60 for mass and r = 0.84 for TEQ). BTH, YRD, and PRD regions exhibited the highest contamination and exposure levels, reflecting intensive industrial activities. Animal-derived foods dominated dietary exposure (∼92.7%), mainly eggs, milk, fish, and pork. Urban populations experienced 1.92-6.51 times higher exposure than rural populations, with larger disparities in industrialized regions. Children aged 2-5 years had the highest exposure. Incorporating cooking-related bioaccessibility reduced the daily dose by 86.6 ± 1.7%, 75.7 ± 0.62%, and 80.6 ± 0.95% under boiling, frying, and Chinese-style cooking, respectively. This study highlights spatial disparities in dietary exposure and the importance of considering cooking processes in exposure assessments, providing insights for region-specific food safety management and pollution control.

Urban waters are widely contaminated with co-occurring microplastics and antibiotics. Human-land interactions (e.g., wastewater discharge, stormwater runoff, and land use) drive contaminant distribution and antimicrobial resistance. Nevertheless, there is a lack of systematic research evaluating the role of co-occurring contaminants in shaping the spread of antibiotic resistance genes (ARGs). In this study, a metagenomic approach was used to characterize the diversity and distribution of ARGs based on contaminant co-occurring patterns. The random forests and partial least squares path model (PLS-PM) were used to identify and prioritize the factors impacting ARGs, leading to a thorough environmental health ecological risk evaluation. Industrial waters, especially pharmaceutical factories, were significant reservoirs and hotspots for the development of ARGs. Urban estuaries further gathered and amplified the effects of co-occurring contaminants, thereby enhancing the prevalence of ARGs. The potential spread of ARGs was dominated by contaminant co-occurring patterns in urban waters, whereas microbial communities dominated in sediments. Urban zoning comprehensively affected environmental health risks, indicating that environmental management strategies, such as controlling pollution sources and implementing remediation, should prioritize water bodies in agricultural areas and sediments in commercial/residential areas.

Current research on land-based pollutants entering marine environments often focuses on individual segments, limiting a comprehensive understanding of pollutant migration along the river-estuary-nearshore (REN) continuum. This study investigates the Nandu River continuum on Hainan Island by integrating positive matrix factorization (PMF) source apportionment with XGBoost-SHAP modeling to elucidate antibiotic distribution patterns and their key driving mechanisms. Results showed that antibiotic concentrations decreased along the gradient of river > estuary > nearshore. In the river section, medical (22.91%) and household medication (21.83%) were the dominant sources, whereas livestock and poultry breeding (21.47%) and aquaculture (20.07%) prevailed in the estuary section. In contrast, scientific, educational, and cultural (13.71%) were the primary contributors in the nearshore section. The XGBoost-SHAP model quantified the relative importance of driving factors as follows: emission sources (ES) (61.87 ng/L) > suspended particulate matter (SPM) (17.75 ng/L) > pH (12.18 ng/L). Antibiotic distribution along the continuum was jointly governed by intrinsic chemical responses to environmental gradients, hydrodynamically controlled transport and particle-mediated processes, and differentiated emission inputs. This study provides mechanistic insights into antibiotic behavior in small-to-medium river-marine continuums and offers scientific support for integrated land-sea environmental management.

Anthropogenic nitrogen pollution poses a systemic threat to microbial interaction networks and biogeochemical cycling in groundwater ecosystems, yet the underlying mechanisms remain poorly understood. Employing an endpoint gradient comparison, we conducted metagenomic analyses of urban groundwater under severe nitrogen stress (Shanghai, China; with NH4+ and NO3- concentrations ∼28× and ∼10× background levels, respectively) versus a near-pristine mountain aquifer (Calistoga, USA). This revealed a multi-level collapse and adaptive restructuring of microbial communities under nitrogen stress. Pollution triggered a fundamental restructuring of bacterial communities, with system type (urban vs. mountain) explaining 74 % of the compositional variation, accompanied by a significant reduction in bacterial alpha-diversity (Shannon index decreased by 34 %) and a taxonomic shift from Actinomycetota-dominated mutualistic networks in the mountain system to Pseudomonadota-dominated communities (> 0.86 relative abundance) in urban groundwater. Functionally, urban systems exhibited multi-pathway suppression of energy-intensive processes, including nitrification (e.g., hao, nxrB genes), methanogenesis, and inorganic sulfur oxidation, aligning with the theory of "pollution-induced metabolic decoupling." To survive, the microbial community pivoted to low-energy strategies, significantly enriching genes for organic sulfur metabolism (e.g., dddT, tsdB), which may exacerbate nitrogen retention by inhibiting denitrifiers via metabolites like H2S. Co-occurrence network topology analysis indicated a catastrophic loss of complexity in urban groundwater, with a ∼90 % reduction in connectivity and a collapse in modularity (from 19.94 to 3.33), alongside an abnormally high proportion of positive correlations (94.4 %), signaling a major loss of ecosystem stability and functional redundancy. Random Forest and redundancy analyses jointly identified ammonium (NH4+) as the core environmental driver of this cascading failure, explaining 86 % of the variance in functional gene profiles and likely disrupting the nitrification pathway through specific suppression of the rate-limiting hao gene (which explained 76 % of the variance in nitrification rates). Based on these insights, we propose a dual-track restoration framework that couples external NH4+ source control with internal microbial network rewiring (e.g., restoring keystone taxa, regulating sulfur feedback loops) to break the nitrogen-sulfur inhibition cycle and restore ecological function. Our findings underscore the critical importance of integrating microbial network resilience into strategies for managing and rehabilitating contaminated groundwater ecosystems.