Potential toxic metal(loid)s (PTMs) pose persistent threats to ecosystems and necessitate robust pollution risk assessments. Accurate environmental baselines are essential for reliable assessment of coastal metal(loid) pollution risks, yet conventional methods often lack spatiotemporal representativeness. This study presents a novel data-driven framework that integrates Positive Matrix Factorization (PMF) with particle-mineral associations to establish site-specific baselines. Temporally-matched baselines were derived by resolving particle migration-dependent components from sediment matrices in two coastal systems (Daya Bay, Pearl River Estuary). Validation shows strong consistency between PMF-derived baselines and traditional geochemical background values in assessing risks for Cd, Cr, Ni, Zn, and Pb using enrichment factors. A significant advantage of the new baseline is its derivation from contemporary metal(loid) concentrations, which ensuring temporal relevance and accounts for spatial heterogeneity through independently generated site-specific baselines. The assessment performance of EF (Optimal R-2 = 1, p < 0.001) in single-element risk assessment demonstrates better linearity than C & fnof; (Optimal R-2 = 0.36, p < 0.001). For multi-element risk index (emRI/mRI), the framework performs comparably or better than traditional approach. Our method enables automated, high-resolution baseline construction for long-term coastal monitoring and provides a robust tool for precision pollution management.

Plant litter input is a fundamental driver of carbon cycling in mangrove sediments. However, the mechanisms by which litter decomposition simultaneously regulates soil organic carbon (SOC) accumulation and destabilization remain poorly understood, limiting our ability to predict the stability of blue carbon ecosystems. Herein, we conducted litter addition experiments combined with three-dimensional excitation-emission matrix fluorescence spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry and proton nuclear magnetic resonance, to assess dissolved organic carbon transformation and stability during litter decomposition. Our results demonstrate that litter decomposition alters mangrove sediment properties, with a higher decomposition rate observed in summer compared to winter. During summer, litter-driven carbon accumulation increased significantly (from 20 to 40 g kg-1), characterized by high microbial activity and decarboxylation reactions, leading to substantial accumulation of labile components (e. g., CCCH, XCCH) and a net increase in SOC lability. In contrast, winter decomposition favored preservation pathways, such as dealkylation and oxygen addition, resulting in the enrichment of recalcitrant, carboxyl-rich alicyclic molecules. This mechanistic insight resolves the apparent paradox of simultaneous stability and instability, demonstrating that litter input is a critical determinant of blue carbon fate. Our findings underscore the necessity of incorporating these seasonal dynamics and molecular-level pathways into models for accurate carbon accounting and sustainable management of mangrove ecosystems.

Potentially toxic metals (PTMs) pose serious ecological threats through bioaccumulation in aquatic food webs, yet the influence of dietary pathways remains insufficiently understood. This study examined how food source contributions regulate PTM bioaccumulation in mangrove gastropods across different seasons and species. PTM concentrations were measured in sediments and four gastropod species (Cerithidea rhizophorarum, Littoraria ardouiniana, Neritina violacea, and Bullacta exarata) collected from the Zhangjiang Estuary, China. Food sources were identified using dual stable isotope analysis (δ13C and δ15N) combined with a Bayesian mixing model (SIAR). Three dominant food sources, i.e., aquaculture phytoplankton (aquaPhyOM), mangrove suspended particulate organic matter (mangroveSPOM), and mudflat benthic microalgae (naturalBMA), were found to drive metal bioaccumulation in gastropod tissues. Their dietary contributions varied across seasons and species. C. rhizophorarum shifted from consuming 69.2 % naturalBMA in summer to 58.6 % mangroveSPOM and 34.6 % aquaPhyOM in winter. B. exarata mainly consumed aquaPhyOM (65.2 %), while N. violacea relied mainly on naturalBMA (59.9 %) during winter. L. ardouiniana exhibited nearly equal contributions from the three food sources (aquaPhyOM: mangroveSPOM: naturalBMA = 27.2 %: 31.5 %: 41.3 %). Notably, food sources interacted with environmental factors to influence metal bioaccumulation. Specifically, ingestion of SPOM may fundamentally change the dominant pathway of Cr uptake in C. rhizophorarum, whereas Mn biodilution intensified with increasing naturalBMA consumption and soft-tissue biomass. These findings redefine patterns of metal bioconcentration, highlighting that trophic pathways play a critical role in PTM transfer rather than passive environmental exposure alone. Future research should quantify metal fluxes across trophic interfaces to better predict ecosystem-level impacts.

Elevated cadmium (Cd) exposure poses a significant threat to plant growth and productivity. Phosphorus (P) alleviates Cd toxicity in plants to some extent; however, the mechanisms underlying this effect remain poorly understood. In this study, the effect of phosphorus on cadmium toxicity was investigated using Kandelia obovata (S., L.) Yong roots from physiological and proteomic perspectives. Under Cd stress, P application was associated with enhanced root activity and antioxidant enzyme functions (peroxidase and superoxide dismutase) within the roots of Kandelia obovata, while concurrently reducing malondialdehyde levels. Proteomic analysis identified 494 and 110 differentially expressed proteins in the cadmium stress vs. the untreated control (Cd vs. CK) group and the exogenous phosphorus addition under Cd stress vs. the phosphorus-only treatment (HP + Cd vs. HP) group, respectively. Enrichment results indicated that P treatment was associated with metabolic adjustments related to cell wall biosynthesis, protein synthesis, and intracellular transport. These coordinated responses suggest that P supplementation may improve Cd tolerance in K. obovata roots.

Highlights What are the main findings? CatBoost was identified as the optimal model for retrieving key water quality parameters (TN, TP, CODMn, and turbidity) from Sentinel-2 imagery, demonstrating superior accuracy and robustness in a dynamic fluvial system. Generalized additive models (GAMs) revealed scale-dependent and nonlinear responses of water quality to natural and anthropogenic drivers across buffer zones ranging from 50 m to 20 km, highlighting the multiphasic effects of factors such as forest cover, land use, and population density. What are the implications of the main findings? This study provides a transferable remote sensing-ML-GAM framework that moves beyond water quality mapping to quantitatively decipher multi-scale driver thresholds, supporting spatially explicit watershed zoning and targeted management strategies. The findings offer actionable insights for differentiated pollution control-such as optimizing riparian buffers for nitrogen and phosphorus interception-and establish a basis for real-time, satellite-based monitoring to track management effectiveness in subtropical coastal rivers.Highlights What are the main findings? CatBoost was identified as the optimal model for retrieving key water quality parameters (TN, TP, CODMn, and turbidity) from Sentinel-2 imagery, demonstrating superior accuracy and robustness in a dynamic fluvial system. Generalized additive models (GAMs) revealed scale-dependent and nonlinear responses of water quality to natural and anthropogenic drivers across buffer zones ranging from 50 m to 20 km, highlighting the multiphasic effects of factors such as forest cover, land use, and population density. What are the implications of the main findings? This study provides a transferable remote sensing-ML-GAM framework that moves beyond water quality mapping to quantitatively decipher multi-scale driver thresholds, supporting spatially explicit watershed zoning and targeted management strategies. The findings offer actionable insights for differentiated pollution control-such as optimizing riparian buffers for nitrogen and phosphorus interception-and establish a basis for real-time, satellite-based monitoring to track management effectiveness in subtropical coastal rivers.Abstract While understanding the drivers of river water quality is crucial, the dependence on ground observations hinders the accurate quantification of driver thresholds, as well as the scale-dependent effects of buffer zones. By transcending the limitations of ground observations, satellite remote sensing provides the spatially continuous data required to define effective buffer zones and determine the threshold intervals for natural and anthropogenic drivers, effectively promoting sustainable watershed management. Herein, we determined the total nitrogen (TN), total phosphorus (TP), permanganate index (CODMn), and turbidity in the Minjiang River of Fujian Province by synergizing Sentinel-2 imagery and in situ data (2021-2024). Subsequently, we further employed generalized additive models (GAMs) considering scale-dependent (50 m to 20 km) characteristics to screen and evaluate the natural-anthropogenic factors influencing the water quality indicators. The GAMs revealed that TN exhibited multiphasic responses to forest cover and water area, characterized by alternating positive and negative effects across their range. TP was found to be predominantly driven by agricultural and urban land use, showing clear scale-threshold effects. This study provides an integrated framework that moves beyond retrieval to quantitatively assess the impact of multi-scale natural-anthropogenic factors, offering actionable insights for precise watershed zoning and science-based management for the sustainable development of river systems.

Soil multifunctionality in riparian zones regulates the transfer of energy, matter, and biodiversity across landscapes, yet the mechanisms sustaining this multifunctionality remain inadequately understood. Here, we conducted a field investigation across subtropical riparian zones along three major rivers in southeastern China-the Minjiang, Jiulong, and Jinjiang Rivers-to examine the relationships between soil microbial biodiversity, cooccurrence network complexity, and soil multifunctionality (SMF). Our finds revealed that fungal alpha-diversity, particularly the richness of symbiotrophic and saprotrophic fungi, and soil organic carbon (SOC) content were the primary biotic and abiotic predictors of SMF, respectively. Additionally, fungal richness, niche width, and the stability of the fungal community were significantly correlated with SMF. Structural equation modeling indicated potential trophic linkages within the microbial food web, where greater diversity of higher trophic levels enhanced SMF, likely through cascading effects on the diversity and composition of lower trophic levels. Notably, the complexity of microbial co-occurrence networks, especially among lower trophic levels, exerted a significant positive influence on SMF. Overall, these results highlight the crucial role of multitrophic microbial network structure in sustaining riparian ecosystem functions. These insights provide a mechanistic framework for riparian ecosystem management, emphasizing that conservation of keystone fungal guilds (e.g., symbiotic and saprotrophic fungi) and enhancement of SOC sequestration should be central to riparian restoration efforts.

Arsenic (As) contamination poses an increasing threat to coastal wetland ecosystems, yet the adaptive strategies of keystone mangrove species remain poorly understood. Here, we investigated the interactive effects of As and iron (Fe) on root morphological, anatomical, and physiological responses in Avicennia marina seedlings using a sand culture experiment. Seedlings were exposed to three As concentrations (0, 10, and 30 μmol L-1) with or without Fe supplementation (100 μmol L-1) for 3 months. Our results showed that As exposure reduced chlorophyll content, root dry weight, and root morphological traits in a concentration-dependent manner, while root porosity and aerenchyma formation increased. Radial oxygen loss (ROL) exhibited a parabolic response, peaking under low As and declining under high As stress. Iron supplementation significantly enhanced ROL (5-fold compared to no-Fe controls) and promoted the formation of Fe plaques on root surfaces, which sequestered As and reduced its translocation to aboveground tissues, as evidenced by increased plaque As content and decreased translocation factors. Anatomical analysis revealed that Fe supplementation further induced looser xylem and phloem cell arrangements with enlarged lumina, facilitating oxygen transport. Correlation and redundancy analyses revealed strong positive associations between ROL and plaque Fe, and negative associations between plaque Fe and As content. Collectively, our findings demonstrate that A. marina employs a coordinated multi-tiered strategy-combining root morphological plasticity, enhanced ROL, aerenchyma formation, and Fe plaque development-to mitigate As toxicity. This study provides mechanistic insights into the adaptive capacity of mangroves under metal (loid) stress and highlights the potential of Fe amendment as a nature-based intervention for restoring contaminated coastal wetlands.

Microplastic (MP) pollution threatens subtropical estuarine wetlands, critical transition zones along the river-estuary-coastal continuum. While these ecosystems serve as sinks and secondary sources of MPs, distribution and burial patterns under varying sedimentary conditions remain poorly understood. Here, this study used high-resolution laser direct infrared (LDIR) imaging to systematically quantify MPs (10-500 μm) in sediment cores from the Zhangjiang Estuary, a subtropical mountain river-estuary system in China. Results show that the average MP abundance ranged from 10,463 to 399,481 items/kg, with corresponding surface areas of 0.61-7.39 cm²/kg. MP concentrations decreased downstream, with enrichment in the surface layer (0-20 cm) and accumulation at depth (up to 80 cm), indicating potential historical deposition based on sedimentation rates. Polymer assemblages, dominated by polyethylene (PE), polyamide (PA), polyurethane (PU), polyethylene terephthalate (PET), and rubber, reflected agricultural, industrial, and domestic sources. MP abundance correlated positively with silt and organic matter content and negatively with salinity and pH, suggesting that fine, organic-rich sediments enhance MP retention, while water-salt dynamics influence vertical long-term burial and downstream transport. Critically, salinity and sediment texture were associated with variations in MP size and polymer composition, which may affect site-specific environmental risk. Estuary exhibited elevated risk due to higher proportions of hazardous polymers such as polyvinyl chloride (PVC) and acrylonitrile butadiene (AB). These findings indicate that MP size and polymer type are important factors for assessing estuarine MP risk, with implications for management across estuary systems.

The composition and reactivity of terrestrial carbon in river networks are crucial components of the global carbon cycle. Yet a key limitation is our inadequate understanding of how hydrological processes and spatial watershed patterns interact to govern the molecular-level composition and biogeochemical reactivity of dissolved organic matter (DOM). To address this, we characterized the spatiotemporal dynamics of DOM across three subtropical rivers in China. By integrating data from ultrahigh-resolution mass spectrometry and excitation-emission matrix spectroscopy with basin characteristics (e.g., land use types, population density), we assessed the molecular composition and reactivity of DOM across rivers and identified key landscape controls. Our findings reveal a dual-control model: anthropogenic activities (e.g., urbanization) shift the DOM pool toward labile, protein-like compounds, whereas natural vegetation (indexed by the Normalized Difference Vegetation Index) enhances the abundance of stable, aromatic compounds, thereby increasing DOM stability. Spatially, the influence of anthropogenic indicators (e.g., impervious surface area) on DOM composition remained statistically significant across wider buffer distances, whereas the influence of natural vegetation was more constrained to riparian zones. This pattern indicates a differential spatial extent of impact mediated by hydrological connectivity. We propose a hierarchical control framework in which watershed characteristics set the primary template for DOM character, and in-stream hydrochemistry acts as a secondary processor that modulates the composition and diversity of riverine DOM. Our findings emphasize that terrestrial carbon composition and reactivity are co-determined by the interplay of watershed characteristics and hydrology, with critical implications for regional carbon budgets under a changing global climate and land use.

Aquatic ecosystems demonstrate distinct dynamic characteristics and function as essential repositories for anthropogenic pollutants. Metal(loid)s can enter food chains through aquatic organism feeding behaviors, accumulate within organisms, and subsequently affect the health of higher trophic-level consumers through trophic transfer. Current research indicates a scarcity of bibliometric studies regrading metal(loid) migration in aquatic ecosystems. This study utilizes bibliometric methods to systematically present research trajectories and focal areas of this rapidly expanding topic, providing comprehensive insights for future research. This field has garnered continuous attention, experiencing accelerated growth after 2005. Research priorities primarily focus on two key areas: metal(loid) bioaccumulation and associated ecological/human health risk assessments. Studies concerning ecological and human health risks have emerged as research frontiers recently. Fish represent the primary research subjects, while scientific attention to sedimentary environments as metal(loid) repositories demonstrates notable growth. Additionally, literature analysis indicates that seminal studies maintain lasting influence on disciplinary development. Given aquatic ecosystems’ essential role as anthropogenic pollutant sinks, studying metal(loid) migration remains crucial for understanding ecosystem health and human welfare. Future research should emphasize enhanced international collaboration, interdisciplinary research, and unified approaches to environmental challenges to advance societal health and safety frameworks.

Soil labile organic carbon (C) fractions play a key role in agricultural soil fertility. However, the effects of long-term organic substitution regimes on soil organic carbon (SOC), its labile fractions, stability, and vegetable yields as well as the relationships among these factors in the open-field are less well-studied. Hence, the objective of this study was to analyze the effects of long-term organic substitution regimes on SOC sequestration, labile C fractions [particulate organic C (POC), microbial biomass carbon (MBC), dissolved organic C (DOC), and readily oxidizable C (ROC)], SOC stability, the C pool management index (CMI), and vegetable yields in a long-term (13 years) open-field experiment. Five treatments were examined: 100% chemical nitrogen fertilizer (CN), substituting 25% of the chemical N with manure (MN) or straw (SN), and substituting 50% of the chemical N with manure (2MN) or manure plus straw (MSN). Compared to the CN, organic substitution treatments increased the average yields of vegetable, the SOC, the labile C fractions’ contents, and the C pool management index (CMI) to varying degrees, but only MSN reached significant levels for these factors. However, the MSN treatment had a significantly lower C stability index (SI) than the CN. 13C-NMR analyses also confirmed that organic substitution treatments increased the proportion of O-alkyl C and the OA/A, but reduced SOC stability. Pearson correlation analysis and the partial least squares path model indicated that labile C fractions were the mainly direct contributors to yield and SOC stability. Overall, substituting 50% of the chemical N with manure plus straw is a relatively ideal fertilization practice to improve vegetable yields and enhance C activity in an open field.

Arsenic (As) contamination in paddy soils disrupts root morphogenesis and radial oxygen loss (ROL), yet the dynamic interplay between iron (Fe) plaque formation and plant physiological adaptation remains poorly understood across temporal scales. This study investigated Fe-mediated mitigation of inorganic As toxicity through hydroponic experiments with varying As (0, 10, and 30 μmol/L) and Fe (0–100 μmol/L) concentrations over exposure periods ranging from acute to chronic scenarios. Pot experiments revealed that 1-week high-As (HAs) exposure reduced chlorophyll content by 28% and suppressed ROL by 50% compared with the control group (CK), whereas prolonged low-As (LAs) exposure induced partial chlorophyll recovery (LAs > CK > HAs). Fe supplementation enhanced root biomass by 1.18–2.39 times under chronic As stress and significantly increased ROL rates by 1.38–2.83 times through Fe-plaque formation, which sequestered 38%–52% of root-associated As. Root porosity peaked at 9.84% under As–Fe co-treatment but showed an inverse correlation with ROL. Anatomical analysis revealed Fe-driven restoration of aerenchyma (46.32% cross-sectional area) and reinforcement of lignification barriers. These findings highlight Fe’s dual role in alleviating As toxicity through physical immobilization and physiological adaptation, offering insights into Fe-based remediation strategies for As-contaminated wetlands.

Disposable masks constitute key microplastic pollutants, as their released mesh-structured microfibers (MS-MFs) demonstrate unique ecosystem penetrability and persistent contamination risks across environmental compartments. However, critical aspects such as microbe-plastic interactions and metabolite transformations remain unexplored fully in wetland ecosystems. This study conducted an in-situ experiment in estuarine wetlands, utilizing integrated material characterization and multi-omics approaches to investigate the environmental transformation of MS-MFs and its driving ecological factors. The findings revealed notable physicochemical changes in polypropylene (PP) materials exposed to the environment, including surface oxidation (46 % increase in the O/C atomic ratio), a 35 % reduction in crystallinity, and accelerated polymer chain scission induced by Fenton-like reactions due to iron adsorption. Metagenomic profiling revealed structured microbial succession, with Pseudomonadati and Bacillati dominating early colonization, transitioning to oxidative stress-tolerant taxa (Vibrio, Jiulongibacter) in later stages. Functional enrichment highlighted biofilm formation and redox-active metabolisms, while metabolomics identified lipid remodeling (arachidonic acid upregulation, sphingolipid suppression) associated with oxidative stress adaptation. These findings revealed microbial colonization patterns where abiotic oxidation, metal catalysis, and microbial activity form a self-reinforcing loop, accelerating polymer breakdown. This study advances mechanistic insights into microplastic dynamics in wetlands and provides a theoretical basis for microbiome-driven remediation strategies.

Fragile mangrove wetlands are threatened by sea level rise, which results in the introduction of increased sulfate concentrations into mangrove sediment. Mangroves are also susceptible to heavy metal contamination, such as arsenic (As) contamination. However, little is known about whether sulfate affects the bioavailability of As in mangrove sediment. This study focuses on the effects of sulfate on arsenic mobilization and transformation in As-contaminated mangrove sediment, and modeled changes in sulfate concentration, As contamination levels, and pH conditions. The As release from sediment treated with sulfate (30 mM) significantly decreased (P < 0.05). In the moderate arsenic-contaminated sediment, the mean arsenic release was 181.95 +/- 33.05 mu g kg(-1) without sulfate and 157.55 +/- 40.98 mu g kg(-1) with sulfate. In addition, the release of As was affected by both pH and sulfate when pH conditions were changed. Arsenic release was promoted at pH 11 (P < 0.05), but sulfate still mitigating As release at this pH value (P < 0.001). Furthermore, the release of As after sulfate input was always accompanied by the release of iron (Fe) and aluminum (Al). Sulfate altered the distribution of forms of As in the sediment, with a significant increase in the proportion of strongly adsorbed As and silicate-bound states of As. Overall, sulfate intrusion mitigates As release, but it also increases the bioavailability of As in the sediment. This fact makes the toxic element most susceptible to long-term mobilization via biological processes. Therefore, the effect of persistent sulfate intrusion caused by sea level rise on toxic elements in mangrove sediment deserves long-term attention. The significance of this study is that it contributes to understanding the behavior of heavy metals in coastal wetland ecosystems affected by sea level rise.

The correlation between soil organic carbon (OC) and iron oxides is recognized as a significant mechanism for the long-term preservation of organic carbon. However, the impact of various phases of iron oxides on OC stabilization in karst ditch wetlands remains unclear. This study was conducted at Caohai National Nature Reserve, the largest karst plateau freshwater lake in China. Forty ditch samples of 0 20 cm soil layer were collected for low-frequency mass magnetic susceptibility (χLF), frequency magnetic susceptibility (χfd

The insufficient control of waste associated with personal protective equipment (PPE) resulted in a large influx of disposable face masks (DFMs) in marine environments. Herein, we investigated the biofilm colonization on three types of polypropylene microplastics (MPs, i.e., DFMs, films, and particles) as well as the potential risks of MP-associated heavy metals (HMs) in seawater. Compared to conventional MP particles and films, DFMs were conducive to colonization by microorganisms and minerals, resulting in the formation of a typical spatial network biofilm structure. This triggered more HM adsorption by the biofilm-developed DFMs through surface complexation with the organic components in the biofilm. By BCR sequential extraction analysis, we found that organic and mineral components comprised 70.2-85.6% and 14.4-29.8% of the HM concentration in the biofilm-developed DFMs, respectively. In an in vitro gastrointestinal tract model, biofilm-developed DFMs had a much higher desorption capacity for HMs than MP particles and films. Moreover, the ecological risk index of biofilm-developed DFMs was significantly higher than that of biofilm-developed films and particles. Considering the potential ecological risk of biofilm-developed DFMs, we advocate that the reasonable recycling and environmentally friendly treatment of PPE MP pollutants should be considered as a bursting challenge for sustainable coastal development.

Glomalin-related soil protein (GRSP) is a significant component in the sequestration of heavy metal in soils, but its mechanisms for metal adsorption are poorly known. This study combined spectroscopic data with molecular docking simulations to reveal metal adsorption onto GRSP's surface functional groups at the molecular level. The EXAFS combined with FTIR and XPS analyses indicated that the adsorption of Cd(II), Sr(II), and Ni(II) by GRSP occurred mainly through the coordination of -OH and -COOH groups with the metal. The -COOH and -OH groups bound to the metal as electron donors and the electron density of the oxygen atom decreased, suggesting that electrostatic attraction might be involved in the adsorption process. Two-dimensional correlation spectroscopy revealed that preferential adsorption occurred on GRSP for the metal in sequential order of -COOH groups followed by -OH groups. The presence of the Ni-C shell in the Ni EXAFS spectrum suggested that Ni formed organometallic complexes with the GRSP surface. However, Sr-C and Cd-C were absent in the second shell of the Sr and Cd spectra, which was attributed to the adsorption of Sr and Cd ions with large hydration ion radius by GRSP to form outer-sphere complexes. Through molecular docking simulations, negatively charged residues such as ASP151 and ASP472 in GRSP were found to provide electrostatic attraction and ligand combination for the metal adsorption, which was consistent with the spectroscopic analyses. Overall, these findings provided new insights into the interaction mechanisms between GRSP and metals, which will help deepen our understanding of the ecological functions of GRSP in metal sequestration.

Eukaryotic microbes play key ecological roles in riverine ecosystems. Amplicon sequencing has greatly facilitated the identification and characterization of eukaryotic microbial communities. Currently, 18S rRNA gene V4 and V9 hypervariable regions are widely used for sequencing eukaryotic microbes. Identifying optimal regions for the profiling of size-fractional eukaryotic microbial communities is critical for microbial ecological studies. In this study, we spanned three rivers with typical natural-human influenced transition gradients to evaluate the performance of the 18S rRNA gene V4 and V9 hypervariable regions for sequencing size-fractional eukaryotic microbes (>180 μm, 20-180 μm, 5-20 μm, 3-5 μm, 0.8-3 μm). Our comparative analysis revealed that amplicon results depend on the specific species and microbial size. The V9 region was most effective for detecting a broad taxonomic range of species. The V4 region was superior to the V9 region for the identification of microbes in the minor 3 μm and at the family and genus levels, especially for specific microbial groups, such as Labyrinthulomycetes. However, the V9 region was more effective for studies of diverse eukaryotic groups, including Archamoebae, Heterolobosea, and Microsporidia, and various algae, such as Haptophyta, Florideophycidae, and Bangiales. Our results highlight the importance of accounting for potential misclassifications when employing both V4 and V9 regions for the identification of microbial sequences. The use of optimal regions for amplification could enhance the utility of amplicon sequencing in environmental studies. The insights gained from this work will aid future studies that employ amplicon-based identification approaches for the characterization of eukaryotic microbial communities and contribute to our understanding of microbial ecology within aquatic systems.

Mangrove ecosystems play a critical role in supporting ecological service values and regulating the global carbon cycle. They have become one of the most highly vulnerable ecosystems in the Anthropocene under the long-term influence of diverse human perturbations. Soil dissolved organic matter (DOM) is an active fraction within the carbon cycle in mangrove ecosystems. However, it remains unclear how human perturbations regulate DOM dynamics. Here, we used the fluorescence method and structural equation modeling to quantify the anthropogenic and environmental influence on soil DOM across the urban development gradient on a national scale in China. Anthropogenic activities (urban construction and sewage discharge) and environmental factors (salinity, metals, pH, and soil organic carbon) were striking forces that shaped DOM quality in mangrove soils. Both indirect and direct effects played critical roles in the soil DOM heterogeneity across the gradient of urbanization. Environmental factors can act as cofactors mediating human impact on DOM pools and as promoters transforming soil DOM in mangroves. Our study provided novel insights into the relationship between coastal developments and mangrove soil DOM heterogeneity and improved knowledge of coastal ecosystems as blue carbon sinks.

Glomalin-related soil protein (GRSP) is a stable iron-organic carbon mixture that can enhance heavy metal sequestration in soils. However, the roles of GRSP in the transformation and fate of Cr(VI) have been rarely reported. Herein, we investigated the electrochemical and photocatalytic properties of GRSP and its mechanisms in Cr(VI) adsorption and reduction. Results showed that GRSP had a stronger ability for Cr(VI) adsorption and reduction than other biomaterials, with the highest adsorption amount of up to 0.126 mmol/g. The removal efficiency of Cr(VI) by GRSP was enhanced (4-7%) by ultraviolet irradiation due to the hydrated electrons produced by GRSP. Fe(II) ions, persistent free radicals, and oxygen-containing functional groups on the GRSP surface as electron donors participated in the reduction of Cr(VI) under dark condition. Moreover, Cr(III) was mainly adsorbed on the -COOH groups of GRSP via electrostatic interactions. Based on 2D correlation spectroscopy, the preferential adsorption occurred on the GRSP surface for Cr(VI) in the sequential order of C--O -> COO--* O-H-* C-O. This work provides new insights into the Cr(VI) adsorption and reduction mechanism by GRSP. Overall, GRSP can serve as a natural iron-organic carbon for the photo-reduction of Cr(VI) pollution in environments.