Soil colloids can significantly enhance spreading of polybromodiphenyl ethers in groundwater by serving as an effective carrier.

Polybromodiphenyl ethers (PBDEs), the widely used flame retardants, are common contaminants in surface soils at e-waste recycling sites. The association of PBDEs with soil colloids has been observed, indicating the potential risk to groundwater due to colloid-facilitated transport. However, the extent to which soil colloids may enhance the spreading of PBDEs in groundwater is largely unknown. Herein, we report the co-transport of decabromodiphenyl ester (BDE-209) and soil colloids in saturated porous media. The colloids released from a soil sample collected at an e-waste recycling site in Tianjin, China, contain high concentration of PBDEs, with BDE-209 being the most abundant conger (320 ± 30 mg/kg). The colloids exhibit relatively high mobility in saturated sand columns, under conditions commonly observed in groundwater environments. Notably, under all the tested conditions (i.e., varying flow velocity, pH, ionic species and ionic strength), the mass of eluted BDE-209 correlates linearly with that of eluted soil colloids, even though the mobility of the colloids varies markedly depending on the specific hydrodynamic and solution chemistry conditions involved. Additionally, the mass of BDE-209 retained in the columns also correlates strongly with the mass of retained colloids. Apparently, the PBDEs remain bound to soil colloids during transport in porous media. Findings in this study indicate that soil colloids may significantly promote the transport of PBDEs in groundwater by serving as an effective carrier. This might be the reason why the highly insoluble and adsorptive PBDEs are found in groundwater at some PBDE-contaminated sites.

Impact of coking plant to heavy metal characteristics in groundwater of surrounding areas: Spatial distribution, source apportionment and risk assessments.

Coking industry is a potential source of heavy metals (HMs) pollution. However, its impacts to the groundwater of surrounding residential areas have not been well understood. This study investigated the pollution characteristics and health risks of HMs in groundwater nearby a typical coking plant. Nine HMs including Fe, Zn, Mo, As, Cu, Ni, Cr, Pb and Cd were analyzed. The average concentration of total HMs was higher in the nearby area (244.27 µg/L) than that of remote area away the coking plant (89.15 µg/L). The spatial distribution of pollution indices including heavy metal pollution index (HPI), Nemerow index (NI) and contamination degree (CD), all demonstrated higher values at the nearby residential areas, suggesting coking activity could significantly impact the HMs distribution characteristics. Four sources of HMs were identified by Positive Matrix Factorization (PMF) model, which indicated coal washing and coking emission were the dominant sources, accounted for 40.4%, and 31.0%, respectively. Oral ingestion was found to be the dominant exposure pathway with higher exposure dose to children than adults. Hazard quotient (HQ) values were below 1.0, suggesting negligible non-carcinogenic health risks, while potential carcinogenic risks were from Pb and Ni with cancer risk (CR) values > 10-6. Monte Carlo simulation matched well with the calculated results with HMs concentrations to be the most sensitive parameters. This study provides insights into understanding how the industrial coking activities can impact the HMs pollution characteristics in groundwater, thus facilitating the implement of HMs regulation in coking industries.

Hydrochemical processes and inorganic nitrogen sources of shallow groundwater in the Sanjiang Plain, northeast China.

This study investigates the chemical characteristics, formation, and sources of inorganic nitrogen (IN) of shallow groundwater across the Sanjiang Plain, aiming to enhance drinking water safety management and pollution control. A total of 167 groundwater and 27 surface water samples were collected for constituents and isotopes (H2 and O18). The hydrogeochemical characteristics showed that the major type is HCO3- Ca·Mg, with low total dissolved solids and a neutral to weak alkaline nature. Rock weathering processes govern the hydrochemical composition of groundwater. Hydrogen and oxygen stable isotopes analyses revealed that precipitation serves as the main water source. In alluvial areas, oxidative conditions lead to the enrichment of NO3-N concentrations, with sewage, manure, and fertilizers being the primary IN sources. In lacustrine areas, intensive rice cultivation results in reductive conditions and strong denitrification processes, causing the loss of NO3-N and leaving NH4-N as the dominant IN form. Organic matter mineralization is likely a more significant contributor to NH4-N concentrations than ammonium fertilizers. These findings provide valuable information for further research on natural sources and groundwater pollution in areas with similar hydrogeological conditions. PRACTITIONER POINTS: Rock weathering processes govern the hydrochemical composition of groundwater, and precipitation serves as the main water source. In alluvial areas, oxidative conditions lead to the enrichment of NO3-N. In lacustrine areas, intensive rice cultivation results in reductive conditions and strong denitrification processes. Organic matter mineralization is likely a more significant contributor to NH4-N concentrations than ammonium fertilizers. These findings provide references for water management and information for further research on natural sources and groundwater pollution in areas with similar hydrogeological conditions.

Hydraulic recharge and element dynamics during salinization in an overexploited coastal aquifer of the world's driest zone: Atacama Desert.

The management of water resources in hyper-arid coastal regions is a challenging task because proper information regarding groundwater recharge and water budget is needed for maintaining the hydraulic balance in optimal conditions, avoiding salinization and seawater intrusion. Thus, this article deals with the estimation of the hydraulic recharge and the study of the effects of salinization on the dynamics of major and trace elements in an alluvial aquifer located in the world's driest zone, the northern Atacama Desert. The result of stable water isotopes (δD and δ18O) and tritium (3H) indicated that groundwater in the area is not recent, whereas 14C results estimated a groundwater residence time ranging between 11,628 and 16,067 yBP. The estimation of the artificial recharge coming from the urban water-supply-system leaks and wastewater/river-water/groundwater infiltration during irrigation was about 19.84 hm3/year, which represents an annual negative water balance of 177 hm3/year for the aquifer. The groundwater salinization triggered by seawater intrusion (up to 32.6 %) has caused the enrichment of Li, Rb, Ca, Ba, and Sr in groundwater by cationic exchange, where the excess of aqueous Na is exchanged by these elements in the aquifer sediments. Other elements such as B, Se, Si, and Sb are enriched in groundwater by ionic strength and/or anionic exchange during salinization. The heightened B concentrations derived from the B-rich alluvial sediments were higher than the limit suggested by international guidelines, representing a risk to consumers. Vanadium seems to be unaffected by salinization, whereas Pb, Mo, As, U, and Zr did not show a clear behavior during saline intrusion. Finally, this article highlights the consequences of conducting improper water management in coastal hyper-arid regions with exacerbated agriculture.

Identification and quantitative estimates of groundwater transfers to formerly charophyte dominated marl lakes with radon-222.

Interaction with groundwater determines many processes in marl lakes. Net transfer of inorganic carbon helps define their chemical characteristics and determines their unique benthic flora. Nutrient enrichment weakens the biogeochemical buffering mechanisms which help maintain a clear-water state and many small, shallow marl lakes are prone to siltation. Despite hydrological processes being recognised as important for the complex interactions between plants, nutrient availability and physical sediment properties which shape marl lake ecology, groundwater discharge to many of these lakes has never been quantified. The aim of this study was to locate and quantify groundwater transfers to degraded marl lakes in a Special Area of Conservation on the island of Ireland. A RAD7 radon detector identified and measured elevated concentrations of 222Rn in three lakes for quantifying their groundwater influx with a 222Rn mass-balance equation. Conservative estimates of mean daily groundwater discharge to Kilroosky Lough, Drumacrittin Lough, and Dummy's Lough were 143 m3, 502 m3, and 269 m3 respectively. With extrapolation to the entire hydrological year, annual groundwater recharge contributed approximately 47 %, 155 %, and 50 % of the respective lake volumes. The areas within the lakes which were found to have the highest groundwater influence also closely matched the locations where substantial charophyte communities persist suggesting that the two are linked. These findings underline the importance of groundwater transfers for the water budget in small marl lakes and will inform management efforts to mitigate their eutrophication.

Perfluorooctanoic acid transport and fate difference driven by iron-sulfide minerals transformation interacting with different types of groundwater.

Perfluorooctanoic acid (PFOA) is an emerging persistent organic pollutant that threatens human health and ecosystems. However, the intricate mechanism of the change in PFOA transport behavior that interacts with FexSy minerals under groundwater-type differences is not clear. To address this knowledge gap, multi-scale experiments and multi-process reaction models were constructed to investigate the underlying mechanisms. The results showed that different groundwater (NO3-, Cl--Na+, SO42-, and HCO3- types) had significant effects on PFOA transport. NO3-, Cl--Na+, SO42-, and HCO3- decreased the retardation effect of PFOA in the FexSy media. Compared to other groundwater types, the adsorption sites of FexSy were the least occupied in the NO3- groundwater. This observation was supported by the least inhabition of λ in FexSy-NO3- interaction system, which demonstrated that more PFOA was in a high reaction zone and electrostatic repulsion was weakest. The surface tension of different ion types in groundwater provided evidence explaining the lowest inhibition in the FexSy-NO3- system. The 2D spatiotemporal evolution results showed that in FexSy with NO3- system, the pollutant flux (6.00 ×10-5 mg·(m2·s)-1) was minimal. The pollutant flux in the SO42- groundwater system was 9.95-fold that in FexSy with the NO3- groundwater. These findings provide theoretical support for understanding the transport and fate of PFOA in FexSy transformations that interact with different types of groundwater.

Hydrogeochemical properties, source provenance, distribution, and health risk of high fluoride groundwater: Geochemical control, and source apportionment.

This study evaluated high fluoride (F-) levels, source distribution, provenance, health risk, and source apportionment in the groundwater of Sargodha, Pakistan. Therefore, 48 groundwater samples were collected and analyzed by ion-chromatography (DX-120, Dionex). The lowest concentration of F- was 0.1, and the highest was 5.8 mg/L in the aquifers. In this study, 43.76% of the samples had exceeded the World Health Organization's allowable limit of 1.5 mg/L. The hydrogeochemical facies in Na-rich and Ca-poor aquifers showed NaCl (66.6%), NaHCO3 (14.5%), mixed CaNaHCO3 (8.3%), CaCl2 (8.3%), mixed CaMgCl2 (2%), and CaHCO3 (2%) type water. Alkaline pH, high Na+, HCO3- concentrations, and poor Ca-aquifers promoted F- dissolution in aquifer. The significant positive correlations between Na⁺ and F- suggested cation exchange, where elevated Na⁺ occurs in Ca-poor aquifers. The cation exchange reduces the availability of Ca2+ would lead to higher F- concentrations. Meanwhile, the correlation between HCO3- and F- indicates that carbonate minerals dissolution helps in increasing pH and HCO3- as a result F- triggers in aquifers. Groundwater chemistry is primarily governed by the weathering of rock, water-rock interaction, ion-exchange, and mineral dissolution significantly control groundwater compositions. Cluster analysis (CA) determined three potential clusters: less polluted (10.4%), moderately polluted (39.5%), and severely polluted (50%) revealing fluoride toxicity and vulnerability in groundwater wells. Mineral phases showed undersaturation and saturation determining dissolution of minerals and precipitation of minerals in the aquifer. PCAMLR model determined that high fluoride groundwater takes its genesis from F-bearing minerals, ion exchange, rock-water interaction, and industrial, and agricultural practices. The health risk assessment model revealed that children are at higher risk to F- toxicity than adults. Thus, groundwater of the area is unsuitable for drinking, domestic, and agricultural needs.

The implications of climate change on freshwater resources in the arid and semiarid Mediterranean environments using hydrological modeling, GIS tools, and remote sensing.

Precipitation partitioning in arid and semiarid environments is not well understood due to scanty precipitation, its temporal distribution, and the lack/absence of adequate measurements of the hydrometeorological components. Simulation methods have the potential to bridge the data gap, thereby providing a window to estimate the water balance components. The present investigation evaluates the water balance components of a typical watershed situated in the southeastern Mediterranean for the period 1979 through 2019 using daily meteorological data and a grid spacing of 250 m. Generated runoff results were commensurate with corresponding values obtained using the SWAT model. Computed groundwater recharge is also compatible with recharge values calculated using the chloride mass balance method. Results show that average runoff and groundwater recharge for the entire period was ⁓24 mm a-1 and 19 mm a-1, giving a precipitation ratio of 9.5% and 7.5%, respectively. Substantial interannual variability in the water balance components was observed during the study period which reflected the significant precipitation fluctuations typifying the Eastern Mediterranean. Results show that the period extending from 1998/1999 through 2018/2019 witnessed an 18% drop in annual precipitation, while surface runoff and groundwater recharge experienced a reduction of ⁓34% and ⁓67%, respectively. Although groundwater recharge is a complex function of numerous meteorological and geological factors, the NDVI can provide an excellent indicator of groundwater recharge in marginal Mediterranean environments. This is highly beneficial in areas where climate records are scanty or absent. The presented results emphasize the significant impacts of global warming and aridification on the future availability of water resources in the semiarid marginal climates in the Eastern Mediterranean and point out clearly that water resources in this area will become scarcer, leading to multiple security threats at national and regional levels.

[Recharge Sources and Hydrochemical Evolution Mechanism of Surface Water and Groundwater in Typical Karst Mining Area].

To study the recharge source, hydrochemical characteristics, and evolution process of karst underground water and surface water in the Xianghualing Mining area, we collected 32 groups of samples from karst underground water and surface water sources in and around the mining area. Based on multivariate statistical analysis, the Piper three-line diagram, Gibbs diagram, and ion ratio coefficient, this study analyzed the hydrogeochemical characteristics of karst underground water and surface water in the Xianghualing Mining area. The study systematically revealed the recharge source, recharge age, and hydrochemical evolution law of both water sources. The results showed that the karst underground water and surface water in the Xianghualing Mining area were weakly alkaline, with the main anions being HCO3- and the main cations being Ca2+. The hydrochemical types mainly included HCO3-Ca, HCO3-Ca·Mg, and HCO3·SO4-Ca·Mg types. Atmospheric precipitation was the primary source of recharge for karst underground water and surface water, and it was also influenced by evaporation during the runoff process. However, the evaporation effect of karst groundwater was relatively small, which was closely related to modern hydrology, and the cycle replacement process was more rapid. The hydrochemical evolution characteristics of karst underground water and surface water were mainly affected by rock weathering, cation exchange adsorption, mineral dissolution, and human activities （such as agricultural and mining activities）. Ca2+, Mg2+, and HCO3- were primarily derived from the dissolution of carbonate minerals, with a small portion also originating from the weathering and dissolution of silicate minerals. Na+ and Cl- were primarily derived from the dissolution of rock salts. Among them, Cl-, NO3-, and SO42- were greatly affected by external inputs from agricultural activities, domestic sewage discharge, and mining activities. The research results are of great significance to the cyclical evolution process of karst underground water and surface water, as well as the protection and utilization of water resources in the Xianghualing Mining area.

[Hydrochemical Characteristics and Variation in Karst Groundwater in the Baiquan Spring Area of Xingtai Over the Last 30 Years].

To elucidate the variation patterns in the hydrochemical characteristics of karst groundwater in the Baiquan Spring area of Xingtai over the past 30 years, an integrated approach utilizing mathematical statistics, Piper trilinear diagrams, Gibbs diagrams, and ion ratio analyses was employed. Comparative analysis was conducted on 62 sets of karst water samples collected during the dry seasons of 1991 and 2020. The findings indicated that the groundwater in the spring area was generally weakly alkaline with a low salinization degree, predominantly characterized by Ca2+ and HCO3- as the dominant ions. Compared to that in 1991, the alkalinity of groundwater in 2020 had intensified, with a general increase in the concentration of various indicators. The hydrochemical types had shifted from the relatively concentrated HCO3-Ca and HCO3-Ca·Mg types to a broader spectrum of types, gradually exhibiting a salinization trend. The distribution characteristics of exceeding components such as TDS, Na++K+, SO42-, and F- showed significant spatial differences. Rock weathering played a pivotal role in the changes observed in the hydrochemical components of groundwater, with enhanced cation exchange and evaporation processes further influencing the hydrochemical characteristics and their spatial distribution.

[Characteristics and Indicative Significance of Groundwater Stable Isotopes in the Loess Plateau at the Regional Scale].

Regional groundwater recharge is a critical scientific issue for sustainable groundwater resource development and management. However, spatial variations in groundwater recharge in the Loess Plateau （LP） remain poorly understood. To fill this knowledge gap, a systematic sampling campaign and stable isotope analysis were carried out for groundwater （shallow aquifer） in 13 major catchments during July 2019. The main objectives of this study were： ① to understandthe spatial distribution and influencing factors of stable isotopes in groundwater and ② to reveal the groundwater recharge sources and pathways and their spatial variations, combined with the precipitation stable isotope datasets. Stable isotopes in groundwater had poor spatial variations at the regional scale； however, they became isotopically depleted with the increase in annual average precipitation on the catchment scale （r = -0.87）. Compared with the stable isotope of precipitation, stable isotopes of groundwater were generally depleted and were similar to the precipitation of the rainy season （July-September）. These together indicated that there was pronounced seasonality of groundwater recharge, and the main recharge period was the rainy season. In particular, the recharge seasonality index （δP/G） was closely related to the catchment's average annual precipitation （r = -0.77） and leaf area index （r = -0.63）. In addition, groundwater lc-excess was generally negative, with the catchment-mean value ranging from -4.3‰ to -0.7‰. Hydrologically, this indicated that groundwater recharge pathways （ratio of matrix flow vs. preferential flow） were different among these catchments, which should be quantitatively determined by combining the saturated zone （groundwater） and the unsaturated zone （soil） in future work. Our findings can improve the understanding of groundwater recharge in LP and provide a scientific basis for sustainable management of groundwater resources at the regional scale.

Mobility and persistence of pesticides and emerging contaminants in age-dated and redox-classified groundwater under a range of land use types.

Understanding groundwater contamination patterns is hampered by the heterogeneous groundwater age and redox status over the depth range typically sampled for identifying pesticides and emerging contaminants threats. This study explores depth patterns of groundwater age and redox status across various land use types, unraveling spatial and temporal trends of pesticides and emerging contaminants using data from groundwater quality monitoring in the south of the Netherlands. The Netherlands is an ideal testing ground due to its high population density and widespread groundwater contamination from multiple sources. 146 multi-level observation wells were age-dated using 3H/3He, and contaminant concentrations were analyzed based on recharge year, land use type, and redox conditions, mitigating uncertainties from spatial and depth-dependent variations in both groundwater age and redox status. Redox-recharge year diagrams were developed to visually evaluate contaminant patterns in relation to these factors and to assess concentration patterns in relation to contamination history. Most detections of pesticides, metabolites, and emerging contaminants occurred in the youngest recharge periods (2000-2010 and 2010-2020) and in agricultural areas. However, certain contaminants, including BAM, desphenyl-chloridazon, short-chain PFCAs, PFOA, and EDTA, were consistently found in older water and Fe- or SO4-reduced conditions, indicating their mobility and persistence in the regional groundwater system. Comparing the presence of contaminants in specific redox classes and recharge periods with known application or leaching history provides insights into retardation (e.g., PFOS) and degradation (e.g., 2-hydroxy-atrazine, benzotriazole), explaining lower detection frequencies in earlier recharge periods. Identifying recharge years from age-dated groundwater helps relate contaminants to farmland application or river water recharge periods, revealing leaching history and contamination origins. The presented framework has the potential to enhance the interpretation of large groundwater datasets from dedicated, short-screened observation wells, such as those from the Danish GRUMO network, the Dutch monitoring networks, and parts of the US National Water Quality Program.

Assessment of physicochemical properties and radioactivity in groundwater at households living in bac Lieu province, vietnam.

This paper presents findings on groundwater physiochemical composition and radioactivity levels in households in Bac Lieu province, Vietnam. Through discriminant analysis, it was observed that groundwater quality exhibits spatial variations corresponding to saline intrusion zones. The paired-samples T-tests revealed significantly different ratios of Ra-224, Ra-226, and Ra-228 isotopes between Na-Cl and Ca-Na-HCO3 water types. All three water types had a ratio of Ra-226/Ra-228 of approximately one, indicating the presence of groundwater aquifers beneath the crust and fluvial marine sediment. Furthermore, strong associations between sulfate and calcium suggest that CO2 enrichment in groundwater aquifers indicates anoxic aquatic environments. Twenty-five of the thirty-three evaluated samples exceeded the national technical regulations for domestic water quality with parameters such as chloride, sulfate, sodium, gross alpha, or total dissolved solids. Fifteen samples exceeded gross alpha's allowable contamination threshold of 0.1 Bq/L. The combination of Ra-226 and Ra-228 did not surpass the U.S. Environmental Protection Agency's recommended limit of 0.185 Bq/L. However, nineteen samples exhibited annual committed effective doses of radium isotopes for infants that exceeded the WHO recommendation of 0.1 mSv/year.

Nitrate sources and transformation in surface water and groundwater in Huazhou District, Shaanxi, China: Integrated research using hydrochemistry, isotopes and MixSIAR model.

Global water resources affected by excessive nitrate (NO3-) have caused a series of human health and ecological problems. Therefore, identification of NO3- sources and transformations is of pivotal significance in the strategic governance of widespread NO3- contaminant. In this investigation, a combination of statistical analysis, chemical indicators, isotopes, and MixSIAR model approaches was adopted to reveal the hydrochemical factors affecting NO3- concentrations and quantify the contribution of each source to NO3- concentrations in surface water and groundwater. The findings revealed that high groundwater NO3- concentration is concentrated in the southwestern region, peaking at 271 mg/L. NO3- concentration in the Wei River and Yuxian River exhibited an increase from upstream to downstream, but in the Shidi River and Luowen River, its concentration was highest in the upstream. Groundwater NO3- has noticeable correlation with Na+, Ca2+, Mg2+, Cl-, HCO3-, TDS, EC, and ORP. In surface water, NO3- level is significantly correlated with NH4+ and ORP. Major sources of NO3- in surface and groundwater comprise manure & sewage and soil nitrogen. Source contribution for surface water was calculated by MixSIAR model to obtain soil nitrogen (57.7%), manure & sewage (23.8%), chemical fertilizer (12%), and atmospheric deposition (6.4%). In groundwater, soil nitrogen and manure & sewage accounted for 19% and 63.8% of nitrate sources, respectively. Both surface water and groundwater exhibited strong oxidation, with nitrification the primary process. It is expected that this study will provide insights into the dynamics of NO3- and contribute to the development of effective strategies for mitigating NO3- contaminant, leading to sustainable management of water resources.

Improving prediction of groundwater quality in situations of limited monitoring data based on virtual sample generation and Gaussian process regression.

The increasing pollution of aquifers by human activities over recent decades poses a threat to drinking water safety. While Gaussian Process Regression (GPR) is a robust tool for predicting and monitoring water quality, its effectiveness is hindered limitations of available data on model training and validation, known as the "small sample problem". Various attempts to resolve this problem include virtual sample generation (VSG). This study aimed to increase the accuracy of GPR for predicting water quality in situations of limited datasets. Three VSG methods, namely Multi Distribution Mega-Trend Diffusion (MD-MTD), Generative Adversarial Network (GAN), and t-distributed stochastic nearest neighbor embedding (t-SNE) were compared for enhancing the accuracy of GPR model prediction of Strontium (Sr2+). The models were used to predict Sr2+ in the shallow aquifer system in Songyuan, Jilin Province. The results showed that t-SNE provided the most significant improvement to the accuracy of the GPR, with R2 increasing from 0.86 to 0.99 (12.98 %), followed by MD-MTD (R2 of 0.95, 9.39 %), with the least improvement obtained by GAN (R2 of 0.92, 5.98 %). Boxplots show that MD-MTD-GPR predictions do not fully capture observed data distributions. GANs accurately replicate the data distribution, while t-SNE-GPR achieves the highest prediction accuracy and handles data fluctuations. GPR accuracy improves with an increasing number of virtual samples but tends to decrease when the number exceeds 258 in this study. This study can guide the improvement of the accuracy of GPR for situations of limited datasets. The results of this study can help improve water quality management and drinking water safety in regions with sparse monitoring data.

Hydrogeochemical differences drive distinct microbial community assembly and arsenic biotransformation in unconfined and confined groundwater of the geothermal system.

High­arsenic (As) groundwater in geothermal aquifers poses a serious threat to public health. Assembly processes governing groundwater microbial community related to As biotransformation are still unexplored in geothermal groundwater across different aquifers. To fill this gap, groundwater microorganisms, community assembly processes, and microbially metabolic coupling of carbon (C), nitrogen (N), phosphorus (P), sulfur (S), and arsenic (As) were investigated in unconfined and confined groundwater in the thermal reservoirs of the Guide Basin. The difference in groundwater hydrogeochemicals led to the heterogeneity of the microbial community and microbially mediated C, N, P, S, and As cycling between unconfined and confined groundwater. Higher temperature and As concentrations, low nutrient supply, and reduced conditions in confined groundwater supported stronger interspecific coexistence and environmental selection, thus promoting the proliferation of As-resistant microorganisms (ARMs) and simplifying the community assemblage. Abundant available nutrient supply and oxidizing conditions supported an increased species diversity and metabolic functionality in unconfined groundwater. S oxidizers, C fixation, and C degradation bacteria potentially contributed to the decreased As concentrations in unconfined groundwater. However, ARMs, ammonification, and anaerobic ammonia-oxidizing bacteria potentially caused As mobilization in confined groundwater. Overall, our results give a comprehensive insight into the interaction between As and microorganisms in geothermal groundwater.

Fate of per- and polyfluoroalkyl substances at a 40-year dedicated municipal biosolids land disposal site.

The fate of per- and polyfluoroalkyl substances (PFAS) was evaluated at a site where municipal biosolids have been applied annually for 38 years as a waste management strategy. Soil cores (1.8 m in 30-cm sections), groundwater from four wells, and biosolids applied in 2022 were analyzed for PFAS (54 targeted, 17 semi-quantified) using liquid chromatography high resolution mass spectrometry including suspect screening. Total PFAS concentrations decreased with soil depth from 1700 ng/g to 2.06 ng/g. PFAS distribution in 2022 biosolids were 60 mol% perfluoroalkyl acid (PFAA) precursors and intermediates. The surface soil was dominated by long-chain PFAAs (67-76 mol%) reflecting precursor degradation after biosolids application. Presence of semi-quantified intermediates further reflects precursor degradation in surface soil. Long-chain PFAAs diminished with depth while short-chain PFAAs increased with up to 94 and 91 mol% short-chain PFAAs in the bottom depth and groundwater, respectively. PFAS distribution with depth is consistent with chain-length dependent sorption-impacted transport and the high organic carbon content of the surface soil (15.2 % OC) which subsequently decreased with depth (~2-3 % OC at >60 cm). High organic carbon content in the upper horizon is likely from decades of high biosolids application rates, which contributed to minimizing leaching of long-chain PFAS. While the well within the dedicated land disposal is not drinking water, for comparison only, PFAS concentrations in this well only marginally exceeded the EU drinking water directive for total PFAS and a few individual short-chain PFAS, but did exceed tenfold, the USEPA drinking water standard for PFOA.

Groundwater discharge and bank overtopping drive large carbon exports from Indian Sundarban mangroves.

The Sundarbans represent the largest mangrove system on earth, covering >10,000 km2. These mangroves can export a vast amount of aquatic carbon that can be potentially sequestered for millennia. However, the mechanisms that drive these processes remain poorly constrained. Here, we estimate porewater-driven carbon exchange between the Sundarbans and the Bay of Bengal using high-resolution time series and a radon groundwater mass balance approach spanning a neap-spring tidal cycle. Submarine groundwater discharge (SGD) increased from neap to spring tides by 352 % up to a maximum of 65.6 cm d-1 largely driven by creek bank overtopping after the mid-tide. Exports of dissolved organic and inorganic carbon and alkalinity doubled between neap and spring, likely due to the 'first flush' of older porewater in the mangrove flats. Groundwater discharge was a significant driver of the net carbon export, contributing up to 86.7 % of DIC and 74.0 % of alkalinity during the spring tide while contributing a lower proportion of DOC (4 %-23 %). If these results are representative of the Sundarbans more broadly, carbon fluxes from the Sundarbans would be more than an order of magnitude higher than some of the world's largest rivers on an areal basis, highlighting the importance of Sundarbans mangroves to global oceanic carbon budgets.

Application of remote sensing and electrical resistivity technique for delineating groundwater potential in North Western Nigeria.

Improving the living condition of residents of Palladan and Basawa community requires access to drinking water. The main objectives of this paper are to identify suitable groundwater zones for productive drilling and to assess groundwater mineralization in the coastal aquifers of the study area. Geographic Information Systems (GIS) and Analytical Hierarchy Process (AHP) were used in the methodology to generate the groundwater potential map. Slope, landcover/land use, lineament density, rainfall, soil cover and drainage density were taken into account to characterize the groundwater potential zones. Weights were assigned to the various parameters and their characteristics according to their impact on groundwater recharge. The groundwater potential map was classified into five zones namely: poor, fair, moderate, good, excellent. Based on the lineament density map, the distribution of these lineaments reveals the degree of porosity or permeability in each area and, consequently, its groundwater potential. Aeromagnetic data filtering permits the construction of a structural map that illustrates various geophysical lineaments that are known to be fault systems in the research area. These faults are the main routes via which groundwater seeps into the subsurface and granitoid-type magnetic rocks intrude into the basement. The research region is badly fractured/failed and made up of four lithologic units, including the aquifer layer (clayey sands in the cracked basement) with thicknesses varying from 12-55 m, according to the vertical electrical sounding (VES) applications. According to geoelectric cross-sections, the subsurface structures are made of granitic rocks that are surrounded by normal faults that trend both NW and NE. It is believed that groundwater flows into the hard rock aquifers in the studied locations through these notable geological features, such as faults and fractures. Two phenomena are responsible for the mineralization of water: a process of interaction between water and rock; and a process of salinization resulting from natural phenomena or anthropic activities. The present study could guide hydrogeological investigations and groundwater resource management planning in the study area.

Groundwater quality prediction and risk assessment in Kerala, India: A machine-learning approach.

Despite its critical importance for health, agriculture, and the economy, and its key role in supporting climate change adaptation, groundwater quality remains vulnerable to contamination and is often neglected until significant deterioration. The groundwater resources of Kerala, one of the southernmost states of India, are under escalating stress and scarcity, despite a high well density with 62% of the population relying on groundwater from approximately 6.5 million open wells. This study investigates the detailed hydrogeochemistry and predicts groundwater quality zones of the state using machine-learning techniques viz, extreme gradient boosting (XGBoost), support vector regression (SVR), artificial neural network (ANN) and random forest (RF) regression. The hydrogeochemical analysis reveals varying groundwater quality across the state. Among the different machine learning models, RF shows higher goodness of fit (R2: 0.922) with minimal prediction error (root mean square error: 6.29 and mean absolute error: 3.12). The predicted groundwater quality was validated using the spatially distributed stiff diagrams, visually representing water composition trends of each well. The very good, good, moderate and poor groundwater quality zones occupy 31.7%, 40.4%, 20.4%, and 7.4% of the state aligning accurately with the groundwater quality scenario of the state. Additionally, groundwater drinking risk assessment was conducted, considering that 7.4% of the state experiences poor-quality groundwater. Integrating groundwater quality maps with population data, the study assessed potential health risks due to consuming untreated water. Nearly 0.59 million people across 252 local self-government bodies (LSGs) are susceptible to consuming poor quality groundwater, which may pose potential health risks. This observation provides valuable insights for sustainable groundwater management and public health safeguarding and the findings of the present study are useful for achieving sustainable development goal (SGD) 6 (clean water and sanitation) and long-term groundwater management in Kerala.