Iodine is essential, yet excessive iodine in groundwater threatens water quality and public health. Denitrification, a widely distributed biogeochemical process in groundwater systems, plays a key role in regulating iodine behavior. We investigated denitrification driven iodine mobilization in high-iodine groundwater from Tianjin's Binhai area through laboratory simulations integrating redox conditions, salinity gradients, and bioaugmentation. The results showed that salinity and redox conditions reshaped the structure and metabolic activity of denitrifying communities. Low total dissolved solids (TDS) and more reducing conditions promoted the increased relative abundance of denitrification-related genera, including Stutzerimonas, Hydrogenophaga, and Pseudomonas. Compared with uninoculated controls, the bioaugmented treatments exhibited stronger iodide (I-) accumulation. Under low TDS (500 mg/L) and high nitrate (NO3-, 100 mg/L) conditions, the denitrification rate constant reached its maximum (23.54 & times; 10(-6) s(-1)), and I- increased most markedly from 18.61 to 700.91 mu g/L. Denitrification genes (e.g., narG and nirS) showed a moderate positive correlation with I- concentrations (r = 0.570, p < 0.05). In the bioaugmented treatments, the contribution of denitrification to I- accumulation was stage dependent: under more oxidising conditions, iodine mobilisation from the solid phase to the aqueous phase was associated with enhanced alkalinity and competitive adsorption by bicarbonate (HCO3-) (r = 0.620, p < 0.001); under more reducing conditions, I- accumulation synchronised with ferrous iron (Fe2+) accumulation, indicating a stronger linkage to iron reduction processes (r = 0.638, p < 0.001).This study reveals a salinity dependent coupling between denitrification and iodine mobilization, providing a framework for managing iodine mobility in coastal aquifers.

Microorganisms play an important role in controlling the transport and enrichment of iodide (I−) in groundwater, thereby exerting a significant influence on drinking water security. To date, most studies on microorganisms and I− migration and enrichment focused on the cultivation of specific microbial species in laboratory environments, and few studies investigated microbial communities and I− in natural environments. To understand the structural characteristics of microbial communities in groundwater with different I− concentrations, the microbial communities in groundwater with different I− concentrations in the coastal area of Tianjin were analyzed. Mantel test, alpha-diversity analysis, LEfSe analysis, co-occurrence network analysis, and PICRUSt2 analysis were employed to examine the microbial data. The results indicated that a total of 392 bacterial genera belonging to 215 families, 122 orders, 42 classes, and 23 phyla (relative abundance > 0.01%) were identified in the groundwater. Proteobacteria, Bacteroidota, Campilobacterota, and Actinobacteriota were the dominant species in the microbial community. Groundwater microbial communities were positively correlated with water chemistry environmental factors such as pH, Na+, TDS, Ca2+, and Mn2+. The diversity, ecosystem complexity, and richness of microbial communities decreased with increasing I− concentration gradient; with increasing I− concentration gradient, the coverage of species expands, the community structure gradually changes from aggregated to discrete, and the relative independence of each species increases. This study provides basic information for understanding groundwater microorganisms and iodine in Tianjin and similar coastal areas.

AIMS:Microbial carbon fixation is central to carbon cycling and carbon sink functioning in coastal aquatic ecosystems. Although carbon fixation pathways have been increasingly investigated across diverse aquatic environments, comparative evidence remains limited for hydrologically connected yet hydrochemically contrasting coastal groundwater and surface water systems. This study aimed to compare carbon-fixation-associated microbial communities and major carbon fixation pathways across groundwater, river water, and reservoir water in the Tianjin coastal region. METHODS AND RESULTS:We integrated metagenomic sequencing with hydrochemical analyses to characterize carbon-fixation-associated microbial communities and six representative carbon fixation pathways. Surface waters were dominated by bacteria and showed relatively stable community composition, whereas groundwater communities comprised both bacteria and archaea and displayed pronounced spatial heterogeneity. The Calvin-Benson-Bassham cycle was prevalent across all water types, and the reductive tricarboxylic acid (rTCA) cycle was also widely distributed. Groundwater showed higher contributions of the Wood-Ljungdahl pathway, the archaeal 3-hydroxypropionate/4-hydroxybutyrate and dicarboxylate/4-hydroxybutyrate cycles, together with the rTCA cycle, indicating coexisting carbon fixation strategies. Pathway abundance and module completeness further suggested differences in pathway integrity among water types. Total dissolved solids, HCO3⁻, CO32⁻, and dissolved organic carbon were key correlates of carbon fixation gene distribution. CONCLUSIONS:Carbon-fixation-associated microbial communities, pathway distributions, and pathway integrity differed markedly between coastal groundwater and surface waters. Groundwater exhibited enhanced non-CBB cycle potentials and more diversified carbon fixation strategies, highlighting the importance of groundwater processes in evaluating carbon sequestration potential and carbon cycling in hydrochemically heterogeneous coastal aquatic systems.

The coastal zone presents complex hydrodynamic interactions among inland groundwater, reservoir water, and intruding seawater, with important implications for ecosystem functioning and water quality. However, the relative roles of hydraulic connectivity and seawater-driven salinity gradients in shaping microbial communities at the aquifer–reservoir interface remain unclear. Here, we integrated hydrochemical analyses with high-throughput 16S rRNA gene sequencing to investigate bacterial community composition, assembly processes, and co-occurrence network patterns across groundwater_in (entering the reservoir), groundwater_out (exiting the reservoir), and reservoir water in a coastal system. Our findings reveal that seawater intrusion exerts a stronger influence on groundwater_out, leading to distinct chemical profiles and salinity-driven environmental filtering, whereas hydraulic connectivity promotes greater microbial similarity between groundwater_in and reservoir water. Groundwater samples exhibited higher alpha and beta diversity compared to the reservoir, with dominant taxa such as Comamonadaceae, Flavobacteriaceae, and Rhodobacteraceae serving as indicators of seawater intrusion. Community assembly analyses showed that homogeneous selection predominated, especially under strong salinity gradients, while dispersal limitation and spatial distance also contributed in areas of reduced connectivity. Key chemical factors, including TDS, Na+, Cl−, Mg2+, and K+, strongly shaped groundwater communities. Additionally, groundwater bacterial networks were more complex and robust than those in reservoir water, suggesting enhanced resilience to salinity stress. Collectively, this study demonstrates that salinity gradients can override the effects of hydraulic connectivity in structuring bacterial communities and their networks at coastal interfaces. Our findings provide novel microbial insights relevant for understanding biogeochemical processes and support the use of microbial indicators for more sensitive monitoring and management of coastal groundwater resources.

Salinization of reservoir water will affect the utilization of water resources. In this paper, Beidagang Reservoir in Tianjin Binhai New Area is taken as the research object, and the Majuan intake gate is taken as the research point. Through column experiment, the influence of saline groundwater on reservoir water was studied, and the hydrogeochemical changes of reservoir water were studied, and the mechanism of reservoir water salinity is revealed. The change of hydrochemical index concentration will go through three stages: static period, rising period, dynamic balance period. There was a concentration gradient in the vertical direction (10–30 cm). The maximum increase of TDS concentration at the depth of 10 cm is 5.05 g/L, and the increase of TDS concentration at 30 cm is 1.19 g/L.

Basic flow is the main source of runoff during the dry season in the Lena River Basin, and plays an important role in water resource planning and ecological environment protection. A stable basic flow segmentation method is particularly crucial for basic flow research. This study compared 9 basic flow segmentation methods, including digital filtering, sliding minimum method, and time step method, to select the optimal method suitable for the Lena River Basin, in order to determine the basic flow. The results showed that the Boughton Chapman filtering method had the best application effect in the Lena River Basin.

Reservoir water and the adjacent soil are ecologically interconnected yet distinct microhabitats in saline coastal wetland ecosystems, but direct comparisons of their bacterial community composition and assembly remain limited. Here, we integrated high-throughput 16S rRNA gene sequencing with statistical, null model, and network analyses to compare diversity patterns, assembly mechanisms, and interactions of abundant and rare bacterial taxa in both habitats. Soil communities exhibited greater taxonomic diversity but a lower overall abundance, while reservoir communities displayed a pronounced vertical stratification, in contrast to the more spatially uniform soil communities at the sampled scale. Key environmental drivers differed: salinity (reflecting the harsh saline context) and nutrient levels structured reservoir communities, whereas the nutrient availability and cation exchange capacity predominated in soils. Stochastic processes mainly governed the assembly of abundant taxa in both habitats, whereas deterministic selection more strongly structured rare taxa, especially in soils subject to harsh saline conditions. The co-occurrence network analysis revealed higher connectivity and modularity in soils, with moderate taxa acting as critical connectors between modules. In contrast, rare taxa played a pivotal role in sustaining network stability in the reservoir. Together, these findings demonstrate distinct, habitat-dependent assembly mechanisms and ecological roles of abundant and rare bacterial taxa in saline coastal wetland microhabitats, providing insights that can inform wetland conservation and ecosystem management.

The process of dissolved oxygen (DO) dynamics in response to temperature is usually highly complex in climate transition zones (CTZs). The intrinsic mechanism of extreme temperature events driving riverine DO dynamics, especially its significant seasonal variability, has not been fully resolved. In this study, an integrated analytical framework was constructed in the Fen River Basin (FRB), a typical semi-arid-semi-moist climate transition zone in China. This framework integrated Seasonal-Trend decomposition using Loess (STL), XGBoost and Shapley Additive explanation (SHAP) coupled model, and Partial Least Squares-Structural Equation Modeling (PLS-SEM). Through time-series decomposition, factor contribution quantification, and path analysis, this study effectively resolves the challenges in identifying complex seasonal linkages between extreme temperatures and DO fluctuations, as well as the coupled mechanisms of multiple drivers. The results show that: (1) The FRB has been warming significantly (0.368 °C/10a) over the past 51 years, far exceeding global and Chinese regional averages. After 1994, the amplitude of temperature-extreme fluctuations has continued to expand, indicating that the basin has entered an accelerated warming phase; (2) Quantitative analysis based on the STL-XGBoost-SHAP model (test set R2 = 0.787, RMSE = 0.365 mg/L) demonstrated that temperature extremes were the primary drivers of the heightened DO fluctuations in the FRB, with the minimum temperature being the most significant influencing factor, contributing 52.7 %; (3) The seasonal effects of temperature extremes on DO fluctuations were characterised by more complex mechanisms during the summer high-temperature period. The study reveals that temperature extremes in the CTZs exacerbate seasonal fluctuations in DO and provide scientific references for water quality management in response to climate change.

In order to further improve the prediction effect of emerging contaminants and reduce the impact of emerging contaminants on people's lives and property, this paper uses Max-Min method to normalize air pollutant concentration data and meteorological data. Through remote monitoring facilities, the field image data is obtained and uploaded to the cloud server, and the objects and characteristics of digital images are calculated and detected by artificial intelligence system, and an algorithm for estimating pollution source targets according to the backtracking motion of pollutant particles is established. Through experimental research, it is found that the model established in this paper can predict five important parameters that affect the environmental fate of emerging pollutants, and use multi-media environmental models such as fugacity models to calculate the distribution of pollutants in the environment. Therefore, data mining technology can extract effective features in the prediction of emerging contaminants, and combining it with machine learning technology can further improve the identification effect of emerging contaminants and provide a reliable basis for the prevention and control of emerging contaminants.

By collecting groundwater samples, And Piper trilinear diagram, Gibbs diagram, ion-terminal element diagram, ion ratio and PMF model were comprehensively applied to study the chemical characteristics of groundwater and the main ion sources in a construction waste landfill in Xi’an. The results show that the pH of shallow groundwater in this study area spanned from 7.37 to 8.98, the TDS ranged from 172 to 1590 mg-L-1, and the groundwater was neutral to weakly alkaline fresh water. This cations were dominated by Ca2+ and the anions by HCO3− and SO42−, and the water chemistry types showed partitioning, with Ca-HCO3 type dominating, followed by Ca-SO4 type. Construction waste landfill, agricultural activities and water rock action are the major factors affecting the shallow groundwater chemistry in the study area, contributing 41.8

The groundwater chemical characteristics of a chemical industry park in Shandong Province were studied by collecting groundwater samples and using mathematical statistics, Piper three-line graph and Gibbs chart. The results show that HCO3·Cl-Ca, Cl·SO4-Ca and SO4·-Cl-Ca are the main hydrochemical types of carbonate fissure karst water, and HCO3·Cl-Ca and Cl· HCO3-Ca are the main hydrochemical types of clastic pore fissure water. The anions are mainly Cl−, HCO3−, SO42−, and the cations are mainly Ca2+. It is speculated that the ion change is mainly from the dissolution of carbonate sediments and gypsum sediments in the south to the dissolution of gypsum or sulfate sedimentary rocks in the north. Along the northeast to southwest direction, the hydrochemical type changes from Cl-HCO3-Ca → Cl·SO4-Ca type. The shallow groundwater in the park area is affected by water-rock interaction. The deep groundwater is affected by the water-rock interaction, and evaporation and concentration also contribute to it, but the water-rock interaction is dominant.

Due to climate change and ever-increasing groundwater exploitation under the background of population growth and economic development since the 1990s, saltwater intrusion (SWI) into coastal aquifers has been recognized as a significant geo-environmental issue in the Mekong Delta (MKD) in southern Vietnam. Previous research indicated that groundwater over-exploitation mainly causes SWI into deep aquifer and seawater is the dominant source of SWI into deep aquifer, however, whether seawater or saline river water is the dominant source of SWI into shallow aquifer remains unknown. In this study, a 3D groundwater flow and salt transport SEAWAT model was developed and calibrated/validated to simulate the processes of shallow groundwater and surface water interactions and saltwater and freshwater interactions in the Mekong River Estuary within the MKD during 2012–2021. Simulation results indicated that: (1) the saltwater/freshwater wedge within the qh aquifer migrates 4.3 km landward and saltwater (TDS 20–35 kg/m3) storage increases 101.5 % from 2012 to 2021; (2) the dominant source of SWI is seawater from annual perspective; (3) the dominant source of SWI is seawater from November to August (10 months) while is the Bassac River from September to October (2 months) from monthly perspective; and (4) contribution ratios of ocean, the Mekong River, and the Bassac River to SWI during one year were 80.29 %, 3.42 %, and 16.29 %, respectively. The outcome of this study can provide a useful reference for implementation of efficient and effective adaptation strategies of coastal water resources management and eco-environment protection and restoration against SWI in a changing climate in the MKD.

Excessive intake of iodine will do harm to human health. In recent years, high iodine groundwater has become a global concern after high arsenic and high fluorine groundwater. A deep understanding of the environmental factors affecting iodine accumulation in groundwater and the mechanism of migration and transformation is the scientific prerequisite for effective prevention and control of iodine pollution in groundwater. The paper comprehensively investigated the relevant literature on iodine pollution of groundwater and summarized the present spatial distribution and hydrochemical characteristics of iodine-enriched groundwater. Environmental factors and hydrogeological conditions affecting iodine enrichment in aquifers are systematically summarized. An in-depth analysis of the hydrologic geochemistry, physical chemistry, biogeochemistry and human impacts of iodine transport and transformation in the surface environment was conducted, the results and conclusions in the field of high iodine groundwater research are summarized comprehensively and systematically. Stable isotope can be used as a powerful tool to track the sources of hydrochemical components, biogeochemistry processes, recharge sources and flow paths of groundwater in hydrogeological systems, to provide effective research methods and means for the study of high iodine groundwater system, and deepen the understanding of the formation mechanism of high iodine groundwater, the application of isotopic technique in high iodine groundwater is also systematically summarized, which enriches the method and theory of high iodine groundwater research. This paper provides more scientific basis for the prevention and control of groundwater iodine pollution and the management of groundwater resources in water-scarce areas.

The chemical flame retardants represented by organophosphate esters (OPEs) are widely used and have a serious impact on the environment. In this study, we collected data on the exposure levels of ten OPEs in Chinese soils in recent years and performed an ecological risk assessment. The results showed that the levels of OPEs varied considerably throughout different regions of China, with high exposure levels in highly urbanized or industrialized areas such as Guangdong Province and Northeast China, where the mean value was >200 ng/g. The content of OPEs in the soil in industrial and commercial areas was significantly higher than in other regions, indicating that the concentration of OPEs in the soil is closely related to local economic development and the degree of industrialization. Meanwhile, the number of studies reporting on OPEs and their exposure concentrations have increased significantly since 2018. Through the ecological risk assessment, it was found that TCP, EHDPP and TEHP pose high ecological risks. Although some OPEs, such as TCIPP, have low ecological risk levels overall, their high exposure concentrations are still worthy of attention. This study details the general status of OPE contamination in Chinese soils, which can serve as a reference for ecological environmental supervision.

In order to effectively repair groundwater pollution and remove petroleum hydrocarbons, two petroleum hydrocarbon degrading bacteria SYT-1 and SYT-2 were isolated from long-term petroleum hydrocarbon contaminated groundwater. The rescreening experiments showed that the degradation rates of SYT-1 and SYT-2 were 65.16 % and 52.52 %, respectively. SYT-1 and SYT-2 were identified as Moraxella and Acinetobacter. The degrading bacteria SYT-1 and SYT-2 were identified as Moxa and Acinetobacter by physiological and biochemical characteristics and 16S rDNA sequencing. The experimental results provide strain resources and technical support for bioremediation of petroleum pollution in groundwater.

Iodine is one of the essential trace elements in the human body, and excessive or insufficient intake will affect human health. To ensure the safety of drinking water resources, the spatial distribution of iodine content and migration enrichment factors in shallow underground salty water in Tianjin coastal area were studied. The results show that the iodide content of shallow groundwater ranges from ND to 1320 μg/L, and high iodine groundwater (100-300 μg/L) and ultra-high iodine groundwater (>300 μg/L) account for 37.5%, distributed in the east, west, central and south of the study area; iodine-deficient groundwater (＜25 μg/L) accounts for 10%, and iodine-suitable groundwater (25-100 μg/L) accounts for 15%. From north to south and from northwest to southeast, the shallow groundwater in the study area changed from freshwater and brackish water to saline and salt water; the I - concentrations in freshwater, brackish water, and saltwater were significantly different, and the I - concentrations tended to increase with the increase of TDS concentration; the main hydrochemical types in this direction changed from HCO 3 ·Ca-Na→Cl·SO 4 -Na·Mg→HCO 3 ·Cl-Na·Ca→Cl·HCO 3 -Na→Cl-Na type shift; high iodine and ultra-high iodine groundwater chemistry types are mainly Cl-Na types, Cl·HCO 3 -Na type and HCO 3 -Ca·Na type. The main source of iodine in groundwater is marine sediments, and its enrichment mechanism is as follows: stronger reducing environment and groundwater flow promote the dissolution of carbonates containing Ca 2+ , HCO 3 - , SO 4 2- and sulfate minerals, such as gypsum and manganese nitrate; sedimentary iodine is released in the process of dissolution of marine sediments and reduced to I - ; I - migrates with the flow of groundwater; in the eastern part of the study area, the poor permeability of the In the eastern part of the study area, mucky clay is the main soil structure, and groundwater flow is blocked, so I - is enriched here, and the concentration increases under strong evaporation and concentration.

Although the ecological risk of emerging contaminants is currently a research hotspot in China and abroad, few studies have investigated the ecological risk of pesticide pollutants in Chinese coastal sediments. In this study, nine pesticide pollutants included in the “List of New Key Pollutants for Control (2023 Edition)” issued by the Chinese government were used as the research objects, and the environmental exposure of pesticide pollutants in China’s coastal sediments was analyzed. The baseline sediment quality criteria were deduced using the balanced distribution method, and a multi-level ecological risk assessment of pesticides in sediment was performed. The results showed that the nine pesticide pollutants were widespread in Chinese coastal sediments, with concentrations ranging from 0.01 ng·g−1 to 330 ng·g−1. The risk quotient assessment showed that endosulfan and DDT posed medium environmental risks to the Chinese coastal sediment environment, and PCBs posed medium risks in some bays of the East China Sea. The semi-probabilistic, optimized semi-probability evaluation and joint probability curve (JPC) assessments all show that endosulfan and DDT pose a certain degree of risk to the environment.

In this study, a 3D variable-density groundwater flow and salt transport model was developed and calibrated to simulate spatial and temporal variation of groundwater salinity in Binhai New Area located at coastal Tianjin Municipality for tracking saltwater/freshwater interface depth, analyzing saltwater descending velocity, and determining downward saltwater intrusion ceasing time under the background of rigorous groundwater pumping regulations (groundwater pumping rate reducing to zero in 2023). Results indicated that: (1) saltwater/freshwater interface depths in the northern area would increase from 130–170 m to 150–190 m from 2016 to 2031, in the central area would increase from 180–230 m to 210–260 m from 2016 to 2030, and in the southern area would increase from 280–300 m to 300–320 m from 2016 to 2030 and then stay unchanged, respectively; (2) saltwater descending velocities in the northern, central, and southern area decrease linearly and will reach zero in the years of 2031, 2030, and 2030, respectively; and (3) enlargement of the extent of downward saltwater intrusion will cease since 2031 in the northern area or 2030 in the central and southern area. To the best knowledge of the authors, this research is the first effort to unravel the fact of vertical saltwater intrusion (saltwater descending) occurred in coastal Tianjin, which demonstrates an urgent need for rigorous pumping regulations of reducing groundwater exploitation.

Completion of the Binhai Reservoir may experience serious salinization or sudden brackishness, thus affecting the normal water supply function. The research on reservoir water salinization mainly focuses on total salinity, chloride ion, or other single indicators, but the release of sediment salt is a complex process. In fact, during the hydrogeochemical process of sediments and reservoir water, various ions may change to different degrees, and the changes of ions will affect the TDS content, which in turn affects the salinity content of the reservoir water.Therefore, the research on the regularity of salt release also needs to carry out a full analysis of ion indicators, to provide theoretical support for the hydrogeochemical interactions between sediments and reservoir water.Taking Beidagang Reservoir as the research area, through the method of combining field sampling and batch experiment, the change law of salinity and main ion indexes after the mixing of coastal reservoir water and sediment is analyzed to explore reservoir water and sediment. The hydrogeochemical interaction between the objects reveal the mechanism of reservoir salinization. Illation condition of reservoir water and sediment, the water chemical indexes can quickly reach equilibrium. The TDS mass concentration of each sampling point increased rapidly at first, and the salt release reached equilibrium after 30 s. Na + and Cl - were the main ions involved in water-rock interaction; the maximum release amounts of Na + and Cl - were 7 597.25 mg/kg, 11 097.00 mg/kg. The Na + , K + ,Mg 2+ , Ca 2+ , SO 4 2- of each sampling point increased or decreased in different degrees in the sediment-reservoir water interaction. Cl - was increased, HCO 3 - decreased slightly. Except for HCO 3 - and Ca 2+ , the changes of other ions showed the rule of sampling points in the downstream of the reservoir ＞ sampling points in the upstream of the reservoir. During the hydrogeochemical process of sediment-reservoir water, the total salt in the sediment was released, and the changes of each ion in the process of salt release were related to the mass concentration difference of each ion in the sediment and the reservoir water. After mixing with the reservoir water, it will be released into the water, and the ions with very low content in the sediment will be adsorbed into the sediment after mixing with the reservoir water, resulting in the reduction of the ion content in the reservoir water.It can be seen from the experiment that the release of salt from sediments can lead to an increase in the salinity of the reservoir water, resulting in the salinization of the reservoir. In the process of salinization of the reservoir water, Na + , and Cl - are the main ions involved in water-rock interaction. The change in salinity showed the rule of sampling points downstream of the reservoir ＞ sampling points upstream of the reservoir.

采用GMS软件构建临汾盆地地下水数值模型,预测了不同驱动因素情景下地下水位的变化规律,并量化不同驱动因素对地下水位变化的影响程度,发现仅降水情景(枯、平、丰)时,浅层地下水位变幅大于承压地下水水位,降水量由458.8 mm至568.0 mm时,浅层地下水年平均水位变化速率差绝对值为0.11 m;仅压采情景(以2018年开采量为基准)下,浅层地下水位与承压地下水位有较大变化,压采由0％升至50％时,浅层地下水和中深层承压水年平均水位变化速率差绝对值分别为0.16、0.25 m;在汾河水位抬升情境下,仅对河流两侧的浅层地下水产生一定影响.研究结果可为临汾盆地地下水的合理利用提供参考依据.