Concentrations In Groundwater Research Articles

Anthropogenic impact of rare earth elements on groundwater and surface water in the watershed of the largest freshwater lake in China

Limited knowledge exists regarding the potential risks associated with anthropogenic release of rare earth elements (REEs) in the environment. This study aimed to investigate REE signatures in the watershed Poyang Lake, the largest freshwater lake in China. Samples of surface water, wastewater, and groundwater were collected from five rivers discharging into the lake. Results revealed wastewater from wastewater treatment plants contained total REE concentrations from 231 to 904 μg/L, exceeding those found in surface water (0.4 to 1.3 μg/L) and groundwater (0.5 to 416 μg/L). Samples with elevated REE were found in Ca-Mg-Cl/SO4 type waters and exhibited an 18OD deviation from local meteoric water line. Wastewater exhibited a higher positive Gd anomaly compared to surface water and groundwater, attributed to anthropogenic input of Gd (Gdanth). The determined Gdanth concentration ranged from 0.04 to 0.21 μg/L, and from 0.06 to 0.37 μg/L, accounting for 4 % to 21 % and 49 % to 84 % of total Gd concentrations in groundwater and surface water, respectively. Gdanth concentration in wastewater (0.19 to 0.43 μg/L) remained constant in effluent after wastewater treatment. Surface water displayed relatively complex normalized REE patterns influenced by anthropogenic activities and natural processes (weathering and complexation), while groundwater exhibited heavy REEs enrichment, due to carbonate solution complexation. Additionally, Gdanth concentration showed a positive correlation with ΣREE, Pb, Ni, and Co concentrations in groundwater, indicating a good pollution tracing potential. Health risk assessment using the hazard quotient (HQ) suggested higher HQGd values in groundwater compared to surface water. Residents in the eastern part of Poyang Lake were found to face higher risks associated with Gd in groundwater compared to the western part, with infants and children at greater risk than adult males and females. These findings offer valuable insights into environmental behavior and health risks of REEs in aquatic systems impacted by human activities.

Assessing groundwater fluoride contamination scenario in West Bengal, India: A combined approach using meta-analysis, current research, and health risk evaluation

The present study was initiated by the findings of a comprehensive systematic review and meta-analysis, which synthesized all available literature on the patterns and trends of groundwater fluoride (F−) contamination in West Bengal, India. This investigation aimed to provide detailed information on F− contamination at the block level within the state, which is essential for effective monitoring and alleviation efforts addressing the acute and evolving human health concerns in affected areas. This study focuses on the six districts (South 24 Parganas, West Medinipur, Jhargram, East Bardhaman, West Bardhaman and Murshidabad) of West Bengal. Findings from more than 3000 datasets revealed that approximately 10%, 11%, 4%, and 14% of groundwater samples exceeded the safe limit of F− (1.5 mgL−1) from South 24 Parganas, Jhargram, West Bardhaman, and Murshidabad district, respectively. Notably 3% of samples from West Bardhaman displayed class V toxicity where F− concentrations exceeding >10 mgL−1. This research introduces an initial assessment of F− concentrations in groundwater from nine newly identified F− contaminated blocks (Baruipur, Sonarpur, Binpur II, Salanpur, Baraboni, Jamuriya, Pandabeswar, Kandi and Khargram) within the region. Overall, 65 blocks from ten districts have been recognized as F− contaminated zones in West Bengal till 2023. The non-cancerous health risk was found to be disproportionately higher in the western districts (Jhargram, West Bardhaman, and western part of Murshidabad) compared to their southeastern counterparts (East Bardhaman, Paschim Medinipur, and South 24 Parganas). A demographic analysis of health risk indicated infants as the most susceptible group to F− toxicity. The probabilistic health risk at P95 dose for eight blocks further corroborated the heightened vulnerability of infants. These insights offer critical implications for the policy-makers, suggesting an urgent need for tailored health policies to mitigate the risk associated with F− contamination in West Bengal.

Mapping of uranium concentrations in groundwater samples of Davanagere district, Karnataka, India, and assessment of effective dose to the population.

The geomorphology, geohydrology, lithology and ecological features of the area influence the uranium content in groundwater. The groundwater samples were collected from 75 locations of Davanagere district, Karnataka, India. Uranium analysis in the water samples was done using LED fluorimeter, based on fluorescence of dissolved uranyl salts. The uranium concentration in water samples varied from 18.41 to 173.21μgL-1 with a geometric mean of 39.69μgL-1. Higher uranium concentration in groundwater was observed in Harapanahalli and Jagalur taluk of Davanagere district, which falls in the Eastern Dharwar Craton, which is generally known to contain more radioactive minerals than the Western Dharwar Craton. The effective ingestion dose and lifetime cancer risk to the population were calculated using the obtained uranium concentration in drinking water.

Estimation of radon concentration in groundwater in the mining zone of Haryana, India, for lungs and stomach annual effective dose.

The groundwater is being used for drinking and irrigation purposes in vast swathes of the Aravalli Mountain range. Since the radioisotope presence in groundwater is affected by the local mining processes, the radiation monitoring in groundwater of mining regions is of paramount importance. In the present work, we have estimated the 222Rn presence in the mining region of Aravalli in the southern part of Haryana. We measured the Radon concentration in 51 water samples from the intended area using the RAD7 alpha detector. The measured radon concentration in some of the water samples collected from the vicinity of the mining zone is higher than that of the United Nations Scientific Committee on the Effects of Atomic Radiation recommended value. Furthermore, we have estimated the annual effective doses for the lungs and stomach contributed by ingestion and inhalation. Though the calculated dose values in collected samples are not in the critical range, further monitoring of background radiation in the Aravalli region is required.

Prediction of arsenic concentration in groundwater of Chapainawabganj, Bangladesh: machine learning-based approach to spatial modeling.

Groundwater in northwestern parts of Bangladesh, mainly in the Chapainawabganj District, has been contaminated by arsenic. This research documents the geographical distribution of arsenic concentrations utilizing machine learning techniques. The study aims to enhance the accuracy of model predictions by precisely identifying occurrences of groundwater arsenic, enabling effective mitigation actions and yielding more beneficial results. The reductive dissolution of arsenic-rich iron oxides/hydroxides is identified as the primary mechanism responsible for the release of arsenic from sediment into groundwater. The study reveals that in the research region, alongside elevated arsenic concentrations, significant levels of sodium (Na), iron (Fe), manganese (Mn), and calcium (Ca) were present. Statistical analysis was employed for feature selection, identifying pH, electrical conductivity (EC), sulfate (SO4), nitrate (NO3), Fe, Mn, Na, K, Ca, Mg, bicarbonate (HCO3), phosphate (PO4), and As as features closely associated with arsenic mobilization. Subsequently, various machine learning models, including Naïve Bayes, Random Forest, Support Vector Machine, Decision Tree, and logistic regression, were employed. The models utilized normalized arsenic concentrations categorized as high concentration (HC) or low concentration (LC), along with physiochemical properties as features, to predict arsenic occurrences. Among all machine learning models, the logistic regression and support vector machine models demonstrated high performance based on accuracy and confusion matrix analysis. In this study, a spatial distribution prediction map was generated to identify arsenic-prone areas. The prediction map also displays that Baroghoria Union and Rajarampur region under Chapainawabganj municipality are high-risk areas and Maharajpur Union and Baliadanga Union are comparatively low-risk areas of the research area. This map will facilitate researchers and legislators in implementing mitigation strategies. Logistic regression (LR) and support vector machine (SVM) models will be utilized to monitor arsenic concentration values continuously.

Hydrogeochemical characteristics, driving factors, and health risk assessment of karst groundwater in Southwest Hubei Province, China.

In South China, karst groundwater is an important water resource for industrial, agricultural, and drinking purposes. However, karst aquifers are highly vulnerable to pollution, leading to deteriorating karst groundwater quality and posing potential health risks to local residents. In this study, 22 groundwater samples were collected from a karst aquifer in the southwestern part of Hubei Province. The hydrogeochemical characteristics and their controlling factors were examined, and the potential health risks associated with groundwater pollutant concentrations in karst groundwater were assessed. The results showed that the groundwater is slightly alkaline with low chemical oxygen demand values, indicating good water quality. The groundwater facies type was identified as HCO3-Ca at most sample spots, showing low total dissolved solids concentrations. Substantial spatial variations in Na+, CO3 2-, and NO2 - concentrations were found, whereas spatial variations in the K+, Ca2+, Cl-, HCO3 -, and F- concentrations were small. In addition, the dissolution of gypsum deposits and magnesium carbonate sedimentary rocks at sampling sites resulted in groundwater facies types of HCO3•SO4-Ca and HCO3-Ca•Mg, with low total dissolved solids concentrations. The karst groundwater chemistry in the study area was mainly controlled by water-rock interactions, as well as by the dissolution of gypsum deposits and magnesium carbonate sedimentary rocks at specific groundwater sampling sites. The groundwater Cl- concentrations were mainly affected by atmospheric precipitation. NO3 - was mainly derived from atmospheric precipitation, domestic sewage, septic tanks, and industrial activities, whereas SO4 2- was derived from atmospheric precipitation, sulfate rock dissolution, and sulfide mineral oxidation. These results highlight the absence of potential human health risks of NO3 - and F- to infants, children, and adults, as their concentrations are below the corresponding regional background values. In contrast, the potential health risks of Cl- cannot be ignored, particularly for infants. This study offers scientific guidelines for protecting and allocating local groundwater resources.

Hydrology Outweighs Temperature in Driving Production and Export of Dissolved Carbon in a Snowy Mountain Catchment

AbstractTerrestrial production and export of dissolved organic and inorganic carbon (DOC and DIC) to streams depends on water flow and biogeochemical processes in and beneath soils. Yet, understanding of these processes in a rapidly changing climate is limited. Using the watershed‐scale reactive‐transport model BioRT‐HBV and stream data from a snow‐dominated catchment in the Rockies, we show deeper groundwater flow averaged about 20% of annual discharge, rising to ∼35% in drier years. DOC and DIC production and export peaked during snowmelt and wet years, driven more by hydrology than temperature. DOC was primarily produced in shallow soils (1.94 ± 1.45 gC/m2/year), stored via sorption, and flushed out during snowmelt. Some DOC was recharged to and further consumed in the deeper subsurface via respiration (−0.27 ± 0.02 gC/m2/year), therefore reducing concentrations in deeper groundwater and stream DOC concentrations at low discharge. Consequently, DOC was primarily exported from the shallow zone (1.62 ± 0.96 gC/m2/year, compared to 0.12 ± 0.02 gC/m2/year from the deeper zone). DIC was produced in both zones but at higher rates in shallow soils (1.34 ± 1.00 gC/m2/year) than in the deep subsurface (0.36 ± 0.02 gC/m2/year). Deep respiration elevated DIC concentrations in the deep zone and stream DIC concentrations at low discharge. In other words, deep respiration is responsible for the commonly‐observed increasing DOC concentrations (flushing) and decreasing DIC concentrations (dilution) with increasing discharge. DIC export from the shallow zone was ~66% of annual export but can drop to ∼53% in drier years. Numerical experiments suggest lower carbon production and export in a warmer, drier future, and a higher proportion from deeper flow and respiration processes. These results underscore the often‐overlooked but growing importance of deeper processes in a warming climate.

Late Quaternary tectonic uplift and Yellow River evolution create high arsenic aquifers in the Hetao Basin, China

High arsenic (As) groundwater is a global problem primarily originating from As-enriched sediments. The provenance (source) and release mechanisms (sinks) of high As sediment have been identified, but the source-sink transfer is poorly understood, especially the influence of geological and surface processes. In this study, we explore the roles of tectonic movement and Yellow River evolution in provenance formation processes and evaluate the combined effects of provenance and sediment age on the As content of aquifer sediments in the northern Hetao Basin of Inner Mongolia. Based on optically stimulated luminescence (OSL) and 14C dating and detrital zircon U-Pb, As content, and lithological analyses of a 400 m core, we reconstructed As changes over the last 160 ka. Our results show clay deposited in a paleo-lake during the Gonghe movement period in the late Pleistocene (∼100 ka B.P.) is enriched in As (31.8 μg/g) due to significant provenance contributions of the As-bearing Langshan Group under tectonic uplift and mountain erosion. In contrast, clay deposited in the middle Pleistocene (∼160 ka B.P.) has lower As content (7.3 μg/g) due to the Yellow River as the primary provenance. Accordingly, the provenance of basin As forced by tectonic uplift and Yellow River evolution determines the background As of aquifer sediments. After deposition, sediment As content decays over time, with higher decay rates in coarse-grained sands than fine-grained. Overall, both provenance formation and sediment age, representing initial and dynamic states of solid phase As, jointly determine the As content of aquifer sediments. More solid phase As provided by younger sediments from the proximal orogenic provenance and reducing conditions due to frequent river–lake transitions, jointly lead to higher As concentrations in shallow groundwater. The study highlights the potential for using a combined analysis of the tectonic movement-surface processes-environment system to improve understanding of geogenic high As groundwater over global large sedimentary basins in the proximity of young orogenic belts.

20-year permafrost evolution documented through petrophysical joint inversion, thermal and soil moisture data

This study investigates the ground characteristics of the high altitude (3410 m a.s.l.) permafrost site Stockhorn in the Swiss Alps using a combination of surface and subsurface temperature, soil moisture, electrical resistivity and P-wave velocity time series data including a novel approach to explicitly quantify changes in ground ice content. This study was motivated by the clear signal of permafrost degradation visible in the full dataset at this long-term monitoring site within the PERMOS (Permafrost Monitoring Switzerland) network. Firstly, we assess the spatio-temporal evolution of the ground ice and water content by a combined analysis of all available in situ thermal (borehole and ground surface temperature), hydrological (soil moisture) and geophysical (geoelectric and seismic refraction) data over two decades (2002–2022) regarding the driving factors for the spatially different warming. Secondly, we explicitly quantify the volumetric water and ice content and their changes in the subsurface from 2015 to 2022 using a time-consistent petrophysical joint inversion scheme within the open-source library pyGIMLi. The petrophysical joint inversion scheme has been improved by constraining the rock content to be constant in time for six subsequent inversions to obtain consistent changes in ice and water content over the monitoring period based on jointly inverted resistivity and traveltime data. All different data show a warming trend of the permafrost. The ice content modeled from the petrophysical joint inversion has decreased by about 15 vol.% between 2015 and 2022. Changes in ice content are first observed in the lower, south-facing part of the profile. As a result, resistivity and P-wave velocity have been decreasing significantly. Permafrost temperatures measured in the boreholes have increased between 0.5 °C and 1 °C in 20 years. Our study shows the high value of joint and quantitative analysis of datasets comprising complementary subsurface variables for long-term permafrost monitoring.

Groundwater hydrogeochemical processes, water quality index, and probabilistic health risk assessment in an arid and semi-arid environment (Hamedan, Iran)

Groundwater protection requires an understanding of different hydrogeochemical processes and this study synthesised and analysed a large hydrogeochemical dataset (1030 data points over 15 years) of published data in western Iran, to gain a deeper understanding and reveal the main factors controlling groundwater geochemistry. Furthermore, non-carcinogenic effects on human health related to nitrate (NO3−) concentrations were assessed. In terms of the measured parameters, four distinct clusters were identified Ca–HCO3, Na–HCO3, Na–SO4, and Na–SO4–Cl. Cluster 1 (68% of samples) had higher average pH while exhibiting lower average electrical conductivities (ECs), cations, and anions than the other clusters and had a lower average weighted arithmetic than the other clusters. 28.5%, 51.9%, 16.3%, 2.1%, and 1.2% of total water samples rated as excellent, good, poor, extremely poor, and undrinkable, respectively, implying that about 80.4% of the groundwater samples are potable. Multi-linear regression models based on pH and EC values can predict cation and anion concentrations in groundwater with high accuracy. The significance of the findings lies in their potential to facilitate the comprehension, modeling, and eventual forecasting of the fate of anions and cations in semi-arid and arid environments, as well as similar groundwaters, using common water characteristics. In order to lower the non-carcinogenic health risks to the local population, the appropriate actions should be taken. The majority of the region's agricultural areas have primary soil textures that are sandy and prone to NO3− leaching. Therefore, in order to maintain the quality of the groundwater in the study region, excessive use of chemical and organic fertilizers should be avoided. These findings will contribute to understanding and safeguarding groundwater quality, while also informing management strategies in arid and semi-arid regions with similar environmental characteristics.

Environmental fate of monosodium methanearsonate (MSMA)-Part 1: Conceptual model.

Monosodium methanearsonate (MSMA), the sodium salt of monomethylarsonic acid (MMA), is used as a selective, broad-spectrum contact herbicide to control weeds in cotton and a variety of turf. In water, MSMA dissociates into ions of sodium (Na+) and of MMA-, which is the herbicide's active component. Certain soil microorganisms can methylate MMA to dimethylarsinic acid (DMA) other microorganisms can demethylate MMA to inorganic arsenic (iAs). To predict the groundwater concentration of iAs that may result from MSMA application, the processes affecting the environmental behavior of MSMA must be quantified and modeled. There is an extensive body of literature regarding the environmental behavior of MSMA. There is a consensus among scientists that the fate of MMA in soil is controlled by microbial activity and sorption to solid surfaces and that iAs sorption is even more extensive than that of MMA. The sorption and transformation of MMA and its metabolites are affected by several factors including aeration condition, temperature, pH, and the availability of nutrients. The precise nature and extent of each of these processes vary depending on site-specific conditions; however, such variability is constrained in typical MSMA use areas that are highly managed. Monomethylarsonic acid is strongly sorbed on mineral surfaces and becomes sequestered into the soil matrix. Over time, a greater portion of MMA and iAs becomes immobile and unavailable to soil microorganisms and to leaching. This review synthesizes the results of studies that are relevant for the behavior of MSMA used as a herbicide to reliably predict the fate of MSMA in its use conditions. Integr Environ Assess Manag 2024;20:1859-1875. © 2024 The Author(s). Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Contaminant mobilization from the vadose zone to groundwater during experimental river flooding events

Natural river flooding events can mobilize contaminants from the vadose zone and lead to increased concentrations in groundwater. Characterizing the mass and transport mechanisms of contaminants released from the vadose zone to groundwater during these recharge events is particularly challenging. Therefore, conducting highly-controlled in-situ experiments that simulate natural flooding events can help increase the knowledge of where contaminants can be stored and how they can move between hydrological compartments. This study specifically targets uranium pollution, which is accompanied by high sulfate levels in the vadose zone and groundwater. Two novel experimental river flooding events were conducted that utilized added non-reactive halides (bromide and iodide) and 2,6-difluorobenzoate tracers. In both experiments, about 8 m3 of traced water from a nearby contaminant-poor river was flooded in a 3-m diameter basin and infiltrated through the vadose zone and into a contaminant-rich unconfined aquifer for an average of 10 days. The aquifer contained 13 temporary wells that were monitored for solute concentration for up to 40 days. The groundwater analysis was conducted for changes in contaminant mass using the Theissen polygon method and for transport mechanisms using temporal moments. The results indicated an increase in uranium (21 and 24%), and sulfate (24 and 25%) contaminant mass transport to groundwater from the vadose zone during both experiments. These findings confirmed that the vadose zone can store and release substantial amounts of contaminants to groundwater during flooding events. Additionally, contaminants were detected earlier than the added tracers, along with higher concentrations. These results suggested that contaminant-rich pore water in the vadose zone was transported ahead of the traced flood waters and into groundwater. During the first flooding event, elevated concentrations of contaminants were sustained, and that chloride behaved similarly. The findings implied that contaminant- and chloride-rich evaporites in the vadose zone were dissolved during the first flooding event. For the second flooding event, the data suggested that the contaminant-rich evaporites continued to dissolve whereas chloride-rich evaporites were previously flushed. Overall, these findings indicated that contaminant-rich pore water and evaporites in the vadose zone can play a significant role in contaminant transport during flooding events.

Ionic Status of Ground & Surface Water at Madaripur in Bangladesh for Drinking & Agricultural Uses

Water is an essential element for livestock consumption, drinking, agriculture, and aquaculture. The water samples were investigated for Mg, pH, Na, EC, Ca, K, S, and P at Rajoir Upazila, Madaripur Bangladesh to to know the water quality of this upazila for various uses during the November, 2020 to October, 2022 . During the study period, considering Ca in Ground, ponds, and river water samples were averagely 44.30, 46. 23, and 49. 25 mgL-1, respectively. On average, Mg content in Ground, Pond, and River water samples were 59.16, 36.94, and 40.98 mgL-1, respectively. Sodium content in Ground, Pond, and, River water samples were 84.39, 17.48, and 16.12 mgL-1, respectively. The average potassium status of the Ground, Pond, and River water were 3.77, 5.71, and 3.98 mgL-1, respectively. S content of Ground, Pond, and River water averagely 0.62, 0.73, and 0.53 mgL-1, respectively. And the average status of P in the Ground, Pond, and, River were 0.075, 0.06, and 0.196 mgL-1, respectively. Almost all the ground and surface (pond and river) water samples were slightly alkaline and appropriate for drinking, irrigation, livestock farming, and aquaculture. The EC values of the Khalia union were problematic for irrigation and livestock consumption.

Bioconcentration of Per- and Polyfluoroalkyl Substances and Precursors in Fathead Minnow Tissues Environmentally Exposed to Aqueous Film-Forming Foam-Contaminated Waters.

Exposure to per- and polyfluoroalkyl substances (PFAS) has been associated with toxicity in wildlife and negative health effects in humans. Decades of fire training activity at Joint Base Cape Cod (MA, USA) incorporated the use of aqueous film-forming foam (AFFF), which resulted in long-term PFAS contamination of sediments, groundwater, and hydrologically connected surface waters. To explore the bioconcentration potential of PFAS in complex environmental mixtures, a mobile laboratory was established to evaluate the bioconcentration of PFAS from AFFF-impacted groundwater by flow-through design. Fathead minnows (n = 24) were exposed to PFAS in groundwater over a 21-day period and tissue-specific PFAS burdens in liver, kidney, and gonad were derived at three different time points. The ∑PFAS concentrations in groundwater increased from approximately 10,000 ng/L at day 1 to 36,000 ng/L at day 21. The relative abundance of PFAS in liver, kidney, and gonad shifted temporally from majority perfluoroalkyl sulfonamides (FASAs) to perfluoroalkyl sulfonates (PFSAs). By day 21, mean ∑PFAS concentrations in tissues displayed a predominance in the order of liver > kidney > gonad. Generally, bioconcentration factors (BCFs) for FASAs, perfluoroalkyl carboxylates (PFCAs), and fluorotelomer sulfonates (FTS) increased with degree of fluorinated carbon chain length, but this was not evident for PFSAs. Perfluorooctane sulfonamide (FOSA) displayed the highest mean BCF (8700 L/kg) in day 21 kidney. Suspect screening results revealed the presence of several perfluoroalkyl sulfinate and FASA compounds present in groundwater and in liver for which pseudo-bioconcentration factors are also reported. The bioconcentration observed for precursor compounds and PFSA derivatives detected suggests alternative pathways for terminal PFAS exposure in aquatic wildlife and humans. Environ Toxicol Chem 2024;43:1795-1806. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Cation exchange and leakage as dominant processes in controlling salinity and strontium in sandy and argillaceous coastal aquifer: Insights from hydrochemistry and multi-isotopes

Coastal groundwater is crucial for supporting ecosystems and meeting the water needs of coastal communities. However, over-exploitation of groundwater resources, including fresh water and deep brine, leads to groundwater depletion and exacerbates saline intrusion, posing significant challenges to sustainable development. This study focuses on the south bank of Laizhou Bay, a typical area threatened by saline intrusion due to the salt industry’s extraction of deep brine and over-exploitation of fresh groundwater. To assess the impact on salinization processes, we employed hydrochemistry and multi-isotope techniques to study strontium (Sr) distribution and salinization in coastal groundwater, unraveling their origins and explaining hydrochemical processes. The hydrochemical analysis revealed that evaporite dissolution primarily contributes to salinity, especially in deep brine and saline water (TDS > 30 g/L). The relationship between 87Sr/86Sr and chlor-alkali index (CAI) and saturation index (SI) indicated distinct sources of Sr. In fresh and brackish water (<10 g/L), Sr originates from mineral weathering and dissolution (SIs of albite and calcite increase with salinity), while in deep brine and saline water, Sr is influenced by cation exchange (with CAI-Ⅰ and CAI-Ⅱ greater than 0). Additionally, the interplay of anthropogenic input (nitrate), Sr, and EC highlights the differential anthropogenic impact on shallow groundwater, emphasizing the relatively closed environment of deep brine. Multi-isotope analysis showed that the average 87Sr/86Sr of shallow groundwater samples in the cone depression is 0.7112, between that of upstream surface water and shallow groundwater (0.7119) and deep brine and saline water (0.7101), indicating groundwater extraction induces deep brine leakage into shallow groundwater, elevating salinity and Sr concentrations. This poses a direct threat to local water security, including irrigation suitability and health risks of drinking water.In conclusion, we categorized the relationships between 87Sr/86Sr and Sr under different hydrochemical processes into different end-members based on their origins. This offers valuable insights in comparable regions for identifying groundwater salinization and saline intrusion, and the use of Sr and its isotopes can also help trace cation exchange and deep brine leakage in coastal aquifers.

Precipitation, temperature, and landcovers drive spatiotemporal variability of groundwater nitrate concentration across the Continental United States

Groundwater nitrate contamination, especially in agriculturally active regions, is a well-recognized environmental concern. Understanding how this contamination evolves across the continental USA (CONUS) and through time is important to designing effective mitigation strategies. Despite extensive research on nitrate contamination, no existing studies can accurately predict changes in groundwater nitrate concentrations over time across the CONUS. To bridge this gap, we compiled a comprehensive dataset for a systematic evaluation of the potential influence of climate dynamics, landcover changes, and crucial soil and geological properties on groundwater contamination. We employed an interpretable machine learning approach, using 293,775 groundwater nitrate observations and 12 independent variables, to estimate annual groundwater nitrate concentrations at the county level from 2001 to 2020. Our model is the first one capable of accurately forecasting temporal changes in groundwater nitrate concentration across the entire CONUS. Our analysis reveals county level groundwater nitrate concentration changes occurred over the past two decades, particularly in regions initially with high concentrations in 2001, ranging from −16.2 mg/L-N to +6.5 mg/L-N between 2001 and 2020. 27 counties in the country appeared to have new concentrations greater than or equal to the maximum concentration level (MCL) at least once during this period. We revealed direct relationships between groundwater nitrate concentrations and climate factors, including that temperature and precipitation dominate the interannual variability in groundwater nitrate concentration in 75.2 % of counties. Notably, we have established a clear correlation between groundwater nitrate concentration and precipitation. Specifically, when annual precipitation falls below a threshold of about 748 mm, an increase of precipitation can directly result in elevated nitrate concentrations in groundwater, indicating heightened vulnerability to contamination due to climate change. This study forms a pivotal foundation for forecasting groundwater nitrate concentration changes across the continent and assessing the potential impact of climate change on future groundwater nitrate concentrations.

Geofluid behavior prior to the 2018 Hokkaido Eastern Iburi earthquake: insights from groundwater geochemistry

A notable decrease of groundwater Na/K ratios was observed several months before the 2018 Hokkaido Eastern Iburi earthquake (M6.7) at a site approximately 20 km west of the earthquake’s epicenter. To investigate the cause of the decreased Na/K ratios, we analyzed groundwater samples (commercially bottled drinking water) to assess the contribution of deep-derived fluids using Li and Sr isotopic ratios, which are reliable indicators of deep fluid contributions. No pronounced changes in the 7Li/6Li and 87Sr/86Sr ratios were observed; thus, the pre-earthquake decrease of groundwater Na/K ratios did not result from the input of deep-derived fluids. The pre-earthquake decrease in the Na/K ratio observed in this study may instead be related to CO2 influx into the aquifer. The CO2 may have leaked from carbon dioxide capture and storage (CCS), because CCS was in operation near the epicenter of the 2018 Hokkaido Eastern Iburi earthquake. Decreases of the Na/K ratios and increases of the CO2 concentrations in groundwater have been reported before other large earthquakes; thus, CO2 influx into groundwater may be a common phenomenon preceding earthquakes.

Changepoint Analysis of Natural Attenuation in Groundwater Improves Forecasts of Time to Attain Goal

AbstractWhen a remedy is selected for groundwater contamination, the monitoring record is often evaluated to extract rate constants for attenuation of contaminants over time, and the rate constants are used to forecast a time when the concentrations will attain a clean‐up goal. These evaluations typically assume the rate constant does not change. Data from 11 monitoring wells at the former Twin Cities Army Ammunition Plant (TCAAP) were evaluated to test whether this assumption was valid for this site. A previous evaluation at this site (based on data from 1987 through 1999) extracted rate constants that would bring the concentrations of trichloroethylene (TCE) in the 11 wells to the maximum contaminant level (MCL) on or before 2013. By 2020, only four wells had reached the MCL. Piecewise linear regressions were used to model the relationship between time elapsed and concentration of TCE for each well, and to identify any changepoints in the rate of attenuation over time. Each well had at least one changepoint with different TCE attenuation rates on either side of the changepoints. The slope of the most recent segment after the last changepoint provides the best information to forecast concentrations in the future. For four of the wells, that forecast indicated that concentrations of TCE would never reach the MCL. Piecewise linear regression analysis proved to be a valuable tool to detect changes in rate constants, and to update forecasts of the time required for groundwater concentrations to reach a cleanup goal.

Hydrochemical Characteristics, Controlling Factors and Water Quality Evaluation of Groundwater Quality in Kono, Sierra Leone

Groundwater is a major source of drinking water and is considered an imperative component of the accessible water assets across Sierra Leone and many parts of the world. The degradation of groundwater can jeopardize drinking water availability and human health. 29 groundwater monitoring samples with 16 water quality parameters were analyzed. Descriptive statistics, Piper plots, Arc GIS spatial interpolation, Gibbs plots, ion ratio analysis, Wilcox diagram, water quality index (WQI), and entropy-weighted water quality index (EWQI) were used to investigate the hydrochemical characteristics, controlling factors and evaluate the groundwater quality in the study area. The results revealed that the groundwater mean concentration of NO3− in the mining concession was 34.00 mg/L which was above the permissible limit, Ca2+ and HCO3− are higher in the Koidu community compared to the mining concession water, indicating weakly alkaline with dominant anions and cations of HCO3− and Na+ + K+ respectively, and the hydrochemical types were mainly HCO3−·Ca2+ and HCO3− ·Na+. The order of anion concentration in groundwater was HCO3− &gt; NO3− &gt; SO42− &gt; Cl− and HCO3− &gt; SO42− &gt; NO3− &gt; Cl− in the mining concession and the Koidu community respectively. Cations were Ca2+ &gt; Na+, K+ &gt; Mg2+ &gt; Fe²⁺, and Ca2+ &gt; Na+ &gt; Mg2+ &gt; K+ &gt; Fe²⁺ in the mining concession and the Koidu community respectively. The interpretation of WQI and EWQI analysis exhibits 55.17% excellent, 17.24% good, 20.69% medium, 6.90% very poor, and 27.59% excellent, 24.14% good, 34.48% medium, 3.45% poor, and 10.34% very poor water respectively. Most of the sampling sites display similar trends to the WQI and EWQI. The solute source of groundwater was mainly controlled by water-rock interaction, cation exchange and the weathering of silicate and carbonate rocks were jointly the main contributors to the formation of the chemical components of groundwater in the study area, among which the main controlling factors of the groundwater were leaching, precipitate concentration and anthropogenic activities, and sulfate rock and carbonate rock dissolution. The overall water quality in the study area was suitable for human consumption but was polluted to an insignificant extent by mining activities. This study provides theoretical support and a decision-making basis for developing, utilizing, and protecting water resources in the study area.

Coupled redox cycling of arsenic and sulfur regulates thioarsenate enrichment in groundwater

High‑arsenic groundwater is influenced by a combination of processes: reductive dissolution of iron minerals and formation of secondary minerals, metal complexation and redox reactions of organic matter (OM), and formation of more migratory thioarsenate, which together can lead to significant increases in arsenic concentration in groundwater. This study was conducted in a typical sulfur- and arsenic-rich groundwater site within the Datong Basin to explore the conditions of thioarsenate formation and its influence on arsenic enrichment in groundwater using HPLC-ICPMS, hydrogeochemical modeling, and fluorescence spectroscopy. The shallow aquifer exhibited a highly reducing environment, marked by elevated sulfide levels, low concentrations of Fe(II), and the highest proportion of thioarsenate. In the middle aquifer, an optimal ∑S/∑As led to the presence of significant quantities of thioarsenate. In contrast, the deep aquifer exhibited low sulfide and high Fe(II) concentration, with arsenic primarily originating from dissolved iron minerals. Redox fluctuations in the sediment driven by sulfur‑iron minerals generated reduced sulfur, thereby facilitating thioarsenate formation. OM played a crucial role as an electron donor for microbial activities, promoting iron and sulfate reduction processes and creating conditions conducive to thioarsenate formation in reduced and high‑sulfur environments. Understanding the process of thioarsenate formation and the influencing factors is of paramount importance for comprehending the migration and redistribution of arsenic in groundwater systems.