Shallow Groundwater Research Articles

Application of major ions and Sr isotopes to indicate the evolution of river water and shallow groundwater chemistry in a typical endorheic watershed, northwestern China

Studying the hydrochemical evolution of river water and groundwater is vital for comprehending complex regional hydrological cycles and managing water resources. An investigation of hydrochemical evolution mechanism of river water and groundwater was executed in an arid and semi-arid endorheic watershed located in the eastern edge of Qaidam Basin, northwest China, by analyzing major ions and strontium isotopic compositions with the combination of hydrogeochemical methods, PMF model and Pearson correlation analysis. From upstream to downstream, the major ions, 87Sr/86Sr values and hydrochemical types of river water and groundwater show spatial variations. Major ions and 87Sr/86Sr analysis reveal that the hydrochmical compositions of river water and groundwater are primarily attributed to silicate weathering, carbonate weathering, evaporite weathering, and agricultural activity. The contribution of four factors affecting the hydrochemical evolution show obvious spatial variations along the flow path. The hydrochemical compositions of river water from the upstream to downstream are mainly contributed by carbonate and silicate weathering as well as weak evaporite weathering (<25%), which are affected by agricultural activity with a great contribution (>25%) in the middle and lower reaches. The contribution to the hydrochemical compositions of groundwater is relatively small (<25%) for carbonate, silicate and evaporite weathering, but great (>25%) for agricultural activity. This study provides implications for understanding the formation and evolution of water and better watershed water management in that typical endorheic watershed basin and even at larger scales.

Enrichment mechanism of groundwater fluoride and its hydrogeological indications in the Badain Jaran Desert, northwest China

Fluoride (F−) enrichment in groundwater poses significant risks to drinking water safety; however, reports of high F− concentrations in groundwater in a vast desert and its hydrogeological indications are limited. In this study, we collected 275 groundwater samples from various depths in the Badain Jaran Desert (BJD) to investigate the distribution characteristics and enrichment mechanisms of F− in desert groundwater, utilizing hydrochemistry, environmental isotopes, and statistical methods. The results indicate that (1) the groundwater F− concentrations in the mountainous areas, desert areas, and downstream wetland areas are 0.10–9.45 mg/L (average of 3.05), 0.19–58.00 mg/L (average of 4.32), and 0.62–9.91 mg/L (average of 1.99), respectively, with corresponding exceedance rates (>1 mg/L) of 83%, 71%, and 80%. (2) In mountainous areas, F− enrichment mechanisms are attributed to ion exchange, evaporative concentration, and the dissolution of fluoride minerals. In desert areas, F− enrichment mechanisms involves multiple hydrogeochemical processes, with the dissolution of fluoride minerals being the most significant, followed by evaporative concentration and desorption. And evaporative concentration is particularly pronounced in shallow groundwater (depth <4 m). In wetland areas, F− enrichment mechanisms are mainly ion exchange and desorption. (3) The F− concentration characteristics (<2 mg/L) and the significant correlation between F− and HCO3− (R = 0.55, P < 0.01) in the deep groundwater of the desert suggest that groundwater does not originate from deep geothermal sources. (4) Based on the significant differences in groundwater F− concentrations, there is a weak hydrodynamic connection between the groundwater in the Quaternary aquifer and that in the underlying Cretaceous bedrock in desert areas. These findings not only facilitate the safe use of groundwater in desert environments but also provide new insights into the formation, circulation, and evolution of desert groundwater.

Intensive agriculture, a pesticide pathway to >100 m deep groundwater below dryland agriculture, Cordoba Pampas, Argentina

Groundwater pesticide pollution in shallow groundwater is a well-established global phenomenon. However, deep aquifers are widely thought to be naturally protected from such modern contaminants, by confining geological barriers and upwards hydraulic gradients. Here we document pervasive pesticide pollution in >100 m deep artesian wells in a sedimentary aquifer below dryland agriculture. The vertical distribution of key groundwater markers, including numbers and concentrations of pesticides, stable (δ18O & δ2H) and radioactive (3H &14C) isotopes and ion concentrations were used to develop a conceptual model of pollutant transport to deep groundwater. Tritium, stable isotope and pesticide distributions in unconfined groundwater indicate that water table rise to <1 m below the surface (due to anthropogenic landscape modification and periodic flooding), has created a rapid pollutant ‘doorway’ to groundwater. Despite a lack of deep borehole pumping for irrigation, these rising water tables have permanently inverted previously upward hydraulic gradients towards the underlying semi-confined aquifer in some areas. Physical heterogeneities and/or leaky domestic boreholes then act as preferential transport avenues for surface pollutants to both unconfined and semi-confined groundwater. These pathways allow small aliquots of highly contaminated surface water and modern unconfined groundwater to mix with the pre-existing pre-modern deep groundwater, resulting in mixed isotopic signatures in deep wells (e.g., radiocarbon <5 pMC but detectable tritium) and detections of multiple synthetic pesticides in the deep aquifer, including AMPA at concentrations up to 4.93 µg/L and Metolachlor up to 0.015 µg/L. Our results demonstrate how semi-confined deep groundwaters may be contaminated by current agricultural techniques even where deep groundwater exploitation is limited. We urge measures to eliminate these pollutant pathways.

Groundwater driven carbon fluxes in a restored coastal saltmarsh wetland: Implications for coastal wetland restoration

Coastal wetlands play a crucial role in the global carbon cycle, yet they have been extensively degraded over the past decade. Though restoration efforts are underway worldwide, there is limited understanding of the role groundwater plays in transporting dissolved carbon within restored wetlands. Here, we address this knowledge gap by investigating water and carbon fluxes in the restored Tomago Wetlands in coastal NSW, Australia. We aim to 1) quantify surface water exports of the main carbon components, 2) estimate greenhouse gas emissions from the aquatic parts of the wetland, and 3) determine the contribution of groundwater discharge to the surface water carbon export and greenhouse gas emissions from the wetland. Sampling took place following a wet period and a freshening event. A radon mass balance model estimated groundwater discharge contributing 10 % to the surface water flow in the restored wetland. The wetland was a source of four of the five main carbon components including DOC, DIC, alkalinity, and CO2, with most of the exported carbon being in the form of alkalinity. Surface water DOC, DIC, alkalinity, and CO2 exports were, 1.3 ± 0.5, 35.5 ± 13.1, 39.4 ± 14.6 and 6.5 ± 2.1 mmol/m2/d, respectively. The average water to atmosphere flux of CO2 and CH4 were 104 ± 209 (mmol/m2/d) and 21 ± 42 (µmol/m2/d). Groundwater-driven carbon fluxes contributed 100 % of the surface water DOC, 30 % of the DIC, 15 % of the alkalinity exports, and 5 % of the overall CO2 losses (lateral aqueous export + atmospheric emissions) from the wetland, with minor contributions to CH4. Carbon exports from both the wetland and groundwater observed in this restored wetland were found to be lower than those reported in the literature for natural or mature wetlands. This would have important implications when developing carbon accounting methods. Overall, our findings highlight the importance of groundwater in carbon transport within restored wetlands and emphasise the need for inclusion of shallow groundwater dynamics in carbon budgets and inventories of coastal wetlands that have or will undergo restoration.

Effects of long-term saline water irrigation on soil salinity and crop production of winter wheat-maize cropping system in the North China Plain: A case study

Fresh water shortage is a major problem for grain production in the low plain around Bohai Sea in the North China Plain. Relative abundance of shallow saline groundwater could serve as an alternative water resource for use during dry seasons. A continuous 8-year field study was conducted from 2015 to 2023 to assess the effects of salt content in irrigation water on soil salt accumulation and crop production. Fresh water (FW) with electrical conductivity (EC) at 1.6 dS/m and three levels of saline water (SW) with EC at 4.7 (SW1), 6.3 (SW2) and 7.8 dS/m (SW3) were used for irrigation. Results showed that a single irrigation event at the jointing stage of winter wheat increased grain production averagely by 18.6 %, 22.5 %, 12.9 % and 9.5 % compared with a rain-fed treatment (RF) under FW, SW1, SW2 and SW3, respectively. With an additional irrigation applied at flowering stage, both irrigations using FW increased the yield by 28.6 %, and both irrigations using SW2 increased the yield by 19.3 % compared with RF. Negative effects of salt on winter wheat overshadowed the positive effects of increased water supply under two irrigations both using SW. With an irrigation at maize sowing and the subsequent summer rainy season, the yield of maize following winter wheat was not affected by a one-time SW irrigation to the previous crop, but showed a 5.3 % yield reduction when two irrigations of SW were applied. There was no apparent salt accumulation in the top 1 m of the soil profile, but a slight increasing trend in the salt content in the 1–2 m layer of the soil profile under SW2 and SW3 irrigation. No apparent changes in soil physical properties were observed for continuous application of SW. It was suggested that SW with EC not exceeding 6.3 dS/m should be applied for a single irrigation during the winter wheat season. This practice could alleviate the fresh water shortage in this region and allow for the maintenance of a relatively stable yield of winter wheat and maize without the risk of salt accumulation in the soil.

Enhancing smallholder agricultural production through sustainable use of shallow groundwater in the Borkena catchment, Awash River Basin, Ethiopia

ABSTRACT With increasing shallow groundwater use for agricultural purposes, understanding the spatiotemporal variability in recharge rates, storage capacity, and its interaction with surface waters becomes crucial for its sustainable management. An integrated SWAT–MODFLOW model is developed to assess shallow groundwater availability in the Borkena catchment. The model is calibrated using streamflow and static groundwater level data. Results show that groundwater recharge in the catchment is 85 mm/a, representing 11% of the mean annual rainfall. Shallow groundwater resources exist across nearly 42% of the Borkena catchment. The percentage of shallow groundwater withdrawal to groundwater recharge is very low (0.1%), signifying the potential for increased shallow groundwater development. However, caution must be taken as its uncontrolled expansion may result in a high risk of depletion. This integrated modeling is one of the few efforts conducted to provide important information regarding shallow groundwater potential in the Borkena catchment, which is essential for the resilience of small-scale producers in the continued growing water demand and climate change.

Variation in soil water content and groundwater levels across three land cover types in a floodplain of the Kromme catchment, South Africa

AbstractInvasions of floodplains and riparian areas by alien woody species replacing predominantly herbaceous indigenous vegetation have altered the hydrological and ecosystem functioning in catchments. Although existing studies have examined changes in river flows following the establishment or clearing of alien woody vegetation, our understanding of impacts on soil water content and groundwater remains poor. Limited process knowledge restricts our capacity to reliably model and predict the impacts of land cover changes. As such, this work compared temporal variations in soil water content (SWC) and groundwater levels at three locations with different vegetation types: black wattle (Acacia mearnsii) trees, palmiet (Prionium serratum), and grass (dominated by Pennisetum clandestinum spp), within a floodplain site in the Kromme Catchment in the Eastern Cape Province of South Africa. Soil water content and shallow groundwater levels (&lt; 4 m below ground) were monitored from August 2017 to December 2019 using soil moisture probes and piezometers. Rainfall, vegetation type and antecedent conditions were identified as the major factors controlling observed responses. On average, soil water content and water retention were significantly higher (p &lt; 0.05) at the palmiet site, whilst the wattle site had the lowest SWC among the three sites. Shallow groundwater levels were also higher at the palmiet and grass sites and lowest at the wattle site. Results showed the negative impacts of black wattle trees on SWC and groundwater levels. These results are crucial for improved quantitative predictive capacity which would allow for better catchment management, for example, informing water supply planning and guiding restoration programs focusing on alien plant clearing.

Megacity solid waste disposal suitability mapping in Dhaka, Bangladesh: an integrated approach using remote sensing, GIS and statistics.

Selecting suitable Megacity Solid Waste Disposal (MSWD) sites is a challenging task in densely populated deltas of developing countries, exacerbated by limited public awareness about waste management. One of the major environmental concerns in Dhaka City, the world's densest megacity, is the presence of dumps close to surface water bodies resources. This study employed the Geographic Information System (GIS)-Analytic Hierarchy Process (AHP) framework to integrate geomorphological (slope and flow accumulation), geological (lithological and lineament), hydrogeological (depth to groundwater table and surface waterbody), socioeconomic (Land use land cover, distance to settlement, road, and airport), and climatological (wind direction) determinants, coupled by land-use and hydro-environmental analyses, to map optimal dumps (MSWDO) sites. The resulting preliminary (MSWDP) map revealed 15 potential landfill areas, covering approximately 5237 hectares (ha). Combining statistical analysis of restricted areas (settlements, water bodies, land use) with AHP-based ratings, the MSWDO map revealed two optimal locations (2285ha). Additionally, the hydro-environmental analysis confirmed the unsuitability of northern sites due to shallow groundwater (< 5.43m) and thin clay, leaving 11 options excluded. Sites 12 (Zone A, 2255ha) and 15 (Zone B, 30ha), with deeper groundwater tables and thicker clay layers, emerged as optimal choices for minimizing environmental risks and ensuring effective long-term waste disposal. This study successfully integrates remote sensing, geospatial data, and GIS-AHP modeling to facilitate the development of sustainable landfill strategies in similar South Asian delta megacities. Such an approach provides valuable insights for policymakers to implement cost-effective and sustainable waste management plans, potentially minimizing the environmental risks to achieve Sustainable Development Goals (SDGs) 6, 11, 13, and 15.

Spatial distribution and hydrogeochemical processes of high iodine groundwater in the Hetao Basin, China

To understand the genesis and spatial distribution of high iodine groundwater in the Hetao Basin, 540 groundwater samples were analyzed for the chemistry and isotope. Total iodine concentrations in groundwater range from 1.32 to 2897 μg/L, with a mean value of 159.2 μg/L. The groundwater environment was mainly characterized by the weakly alkaline and reducing conditions, with the iodide as the main species of groundwater iodine. High iodine groundwater (I > 100 μg/L) was mainly distributed in shallow aquifers (< 30 m) of Hangjinhouqi near the Langshan Mountain and the discharge areas along the main drainage channels. The δ18O and δ2H values ranged from −12.09 ‰ to −3.99 ‰ and − 91.58 ‰ to −52.80 ‰, respectively, and the correlation between groundwater iodine and isotopes indicates the dominant role of evapotranspiration in the enrichment of iodine in the shallow groundwater with depth <30 m. It was further evidenced by the correlation between groundwater iodine and Cl/Br molar ratio, and significant contributions of climate factors identified from the random forest and XGBoost. Moreover, irrigation practices contribute to high iodine levels, with surface water used for irrigation containing up to 537.8 μg/L of iodine, which can be introduced into shallow aquifer directly. The iodine in irrigation water can be retained in the soil or shallow sediment, and later leach into groundwater under favorable conditions.

Groundwater table prediction and seasonal variation influenced by short rotation willow plantation on marginal riparian lands of the Prairie potholes in Canada

Shallow groundwater consumption via phreatophytic transpiration and resulting vegetation-linked groundwater table (GWT) fluctuation is a typical soil hydrological process in wetland riparian areas. However, upland and riparian land use alterations may further influence the shallow GWT fluctuation, temporally and spatially. In this multi-year field study, we investigated whether introducing short rotation willow (SRW) positively or negatively affects the shallow GWT, soil water availability, and soil health on marginal riparian lands of the Prairie Pothole Region (PPR). We compared the impact of SRW on these parameters to two common land uses: annual crop (AC) and pasture (PA). Depth to GWT was monitored via data loggers from 28 wells in two semi-arid PPR sites. The GWT depth varied by land use practices only in site B (p < 0.001; PA > SRW = AC) but not significantly in site A (p = 0.325), and the patterns were inconsistent between sites. In GWT depth prediction, the performance of Artificial Neural Network (ANN) was better than Autoregressive Integrated Moving Average (ARIMA) models but was inconsistent alike with field observations. The GWT depth responded to seasonal precipitation and potential evapotranspiration (ET) patterns. The monthly GWT fluctuations peaked between June and August due to increased precipitation, while they were lower during May and September with reduced precipitation; however, these variations were not significant (p > 0.05). Higher precipitation and lower potential ET throughout the wet year (i.e., in 2014) significantly (p < 0.05) raised GWT (i.e., decreased depth to GWT) under all land uses, and vice versa. Our study indicated that planting SRW in marginal riparian land of the PPR would not negatively impact shallow GWT or soil water availability. Moreover, the SRW plantation could also help manage soil salinity without severely depleting the soil's nutrient pools or diminishing soil quality and health indicator parameters measured during the first rotation.

Impact of land use on shallow groundwater quality for domestic use in Mathira East Sub-County in Kenya

Shallow groundwater sources of boreholes and springs form major types of water resources used in rural areas of Kenya. Information on their status is inadequate, thus hindering their sustainable management. This study investigated the relationship between land-use types, groundwater sources and water quality. Thirty-six randomly selected groundwater sources were sampled in Mathira East Sub-County from four stratified land-use types of forest, tea, coffee, and urban, with 18 samples collected for either shallow boreholes or springs. The Principal Component Analyses (PCA) grouped groundwater resources into three groups according to groundwater sources and land-use types. Spearman rank correlation, one-way ANOVA and unpaired t-test found that land use types significantly influenced shallow groundwater quality along an increasing gradient of landscape disturbances from the less disturbed forest, then tea, coffee and lastly to the severely disturbed, the urban area. The most affected water parameters were turbidity, conductivity, NO3–N, phosphates and faecal coliforms and their variation was attributed to land-use changes, especially agricultural intensification and urbanisation. The significant variations in other water quality parameters (total hardness, total alkalinity, dissolved oxygen, pH, manganese and fluoride) were attributed to water–rock interactions, climatic factors and land use changes. Calculated Water Quality Index (WQI) with faecal coliforms parameter from groundwater sources were found unsuitable for domestic use, while the ones derived without faecal coliforms parameter were found safe for human use. Overall, shallow groundwater sources were contaminated and unsafe for human use. This study recommends regular monitoring of key water parameters affected by land use changes to support the sustainable management of shallow groundwater resources in Mathira East Sub-County and the larger region of South Sahara Africa.

Hydrogeochemical characteristics and agricultural suitability of shallow groundwater quality in a concentrated coalfield area of Huaibei Plain, China.

Groundwater is one of the chief water sources for agricultural activities in an aggregation of coal mines surrounded by agricultural areas in the Huaibei Plain. However, there have been few reports on whether mining-affected groundwater can be adopted for agricultural irrigation. We attempted to address this question through collecting 71 shallow groundwater samples from 12 coal mining locations. The Piper trilinear chart, the Gibbs diagram, the proportional coefficient of major ions, and principal component analysis were examined to characterize the source, origin, and formation process of groundwater chemical composition. The suitability for agricultural irrigation was evaluated by a final zonation map that establishes a comprehensive weighting model based on analytic hierarchy process and criteria importance though the intercriteria correlation (AHP-CRITIC). The results revealed that the groundwater was classified as marginally alkaline water with a predominant cation of HCO3- and anion of Na+. Total hardness, total dissolved solids, sulfate (SO42-), sodium (Na+), and fluoride (F-) were the primary ions that exceeded the standard. The results also indicated that the dominant hydrochemical facies were Ca-HCO3 and Na-Cl. The dissolution of carbonate, silicate, sulfate minerals, along with cation exchange, were the main natural drivers controlling the hydrogeochemical process of groundwater. The zonation map suggested that 43.17%, 18.85%, and 37.98% of the study area were high, mediate, and low suitability zones, respectively. These results from this study can support policymakers for better managing groundwater associated with a concentration of underground coal mines.

Surface wave monitoring using ambient noise for detecting temporal variations in underground structures in landslide area

The temporal variation in subsurface structure of a landslide area was monitored using spatial autocorrelation (SPAC) as a simple and robust seismic observational method. The SPAC method is often used in civil engineering to estimate one-dimensional (1D) subsurface structures. However, in this study, we monitor the temporal variation in the SPAC coefficient deviation to evaluate environmental change effects and changes in the subsurface velocity structure. We used a seismic array comprising 10 seismometers in a landslide-prone area in Morimachi Town, western Shizuoka Prefecture, Japan, and continuous observations were performed from October 2020 – May 2022. We obtained a 1D velocity structural model as a reference using the multi-mode SPAC (MMSPAC) method with the averaged SPAC coefficients at different distances for all observation periods. We calculated the daily variation in SPAC coefficient relative to the average for all observation periods. We then applied cluster analysis to the SPAC coefficient deviation, which revealed weekly changes likely due to human activity and the effect of stream surges on nearby streams. After removing stream surge clusters and correcting for the weekly change, we reapplied cluster analysis to identify two major clusters. The differences between the two clusters can be attributed to structural changes in the very near surface (∼5 m) and deeper parts (∼20 m), likely influenced by shallow groundwater due to rainfall. By investigating the location of the landslide mass near the observation site, we suggest that structural changes around 20 m deep may correspond to the depth of potential slip surfaces.

Response of Antioxidant Enzymes of Winter Wheat (Triticum aestivum L.) to Shallow and Saline Groundwater Depths

ABSTRACTAntioxidant enzymes in plants are critical for protection against oxidative stress and for the overall health and resilience of plant systems. However, antioxidant responses of plants grown in shallow and saline groundwater are poorly understood. Therefore, understanding the biochemical responses of plants to shallow groundwater significantly affects food security and environmental conservation. With this aim, the present work was carried out for 2 years in drainable lysimeters to assess the effects of four different groundwater salinities (0.38, 2.0, 4.0 and 8.0 dS m−1) on the temporal changes in antioxidant enzymatic activity in wheat plants under three different groundwater depths (30, 55 and 80 cm). Superoxide dismutase (SOD), glutathione S‐transferase (GST) and catalase (CAT) activities varied significantly based on groundwater depth and salinity. CAT and GST enzyme levels increased curvilinearly with rising groundwater depth and salinity. Conversely, the GR enzyme activity showed no significant change with groundwater depths but increased linearly with higher salinity. SOD enzyme activity notably increased at a groundwater depth of 30 cm but decreased at a depth of 80 cm. Moreover, the peak activity of the GR enzyme was observed at a 6 dS m−1 groundwater salinity under groundwater depths. Additionally, the GST and CAT enzyme activities were inhibited more when the groundwater depth was &lt;55 cm and the groundwater salinity was &gt;4.20 dS m−1. Finally, identifying the peak levels of antioxidant enzymes could potentially serve as an indicator for determining the optimal timing for applying stress mitigation methods in areas with shallow and saline groundwater.

Pollution evaluation and health risks assessment of naturally occurring toxic metals in shallow groundwater: A study in southwestern tidal delta of Bangladesh

Groundwater is the main source of potable water in rural regions of Bangladesh. Still, contamination with potentially harmful metals due to natural processes and anthropogenic activities leads to various health impacts. The focus of this research was to determine the extent of metal contamination in shallow groundwater from three southwestern districts of Bangladesh and the health hazards associated with it. A comprehensive analysis of metal, including metalloid, copper (Cu), aluminum (Al), chromium (Cr), Arsenic (As), Manganese (Mn), and boron (B) was performed on a set of 51 samples. Groundwater samples were analyzed for contamination using Atomic Absorption Spectroscopy and a UV–VIS Spectrophotometer, with pollution levels assessed via indices like the Metal Evaluation Index, Nemerow Pollution Index, and Contamination Index. Human health risks were evaluated through Chronic Daily Intake, Hazard Quotient, and Hazard Index calculations following USEPA guidelines. The results indicate that arsenic levels exceeded 25 samples and manganese levels exceeded 34 samples in accordance with WHO drinking water standards. Boron (B) concentrations exceeded the threshold in seven samples, whereas Al, Cu, and Cr exceeded limits in only two samples. The metal evaluation index (MEI), Nemerow pollution index (NI), and degree of contamination (Cd) revealed moderate to severe contamination in groundwater and unsuitability for drinking purposes. Out of the 51 analyzed samples, 48 samples exhibited potential non-carcinogenic health risks for adults, while all samples exceeded the hazard index (HI) threshold value (01) for children. Concentrations of As and Mn were identified as the main contributing factors to the higher HI values in both adults and children. However, the concentrations of Cu, Al, Cr, and B in groundwater were not individually found to be as risky. This study provided valuable insights to conduct a future comprehensive investigation of the designated region to delineate safe and hazardous zones for the installation of shallow tubewells. Furthermore, there's a need to enhance public awareness regarding the long-term ramifications of consuming contaminated water.

Effects of grid resolution on regional modelled groundwater salinity and salt fluxes to surface water

Coastal fresh groundwaters face growing threats from rising withdrawals and climate change, with salinization of surface and groundwater as notable impacts. Recent developments in parallel variable-density modelling enable studying these threats at unexplored resolutions and extents. To improve the understanding of ground- and surface water salinization processes, we designed an experiment to measure how spatial resolution affects both groundwater salinity distribution and salt loads to surface waters. An existing parallelized coupled variable-density groundwater flow and salt transport (VD-GWT) model is applied to a region in the Netherlands whereby the surface water drainage network is parameterized at grid resolutions between 10 and 250 m. The results show a strong dependency between resolution and the salinity distribution in shallow groundwater while simulated salt loads are affected by imperfect flux scaling. The computational resources needed for this test suggest that regional high-resolution VD-GWT models are feasible using HPC environments, albeit not practical.

Characterization, formation mechanism, and human health risk assessment of fluoride in shallow groundwater of Suzhou city, East China

ABSTRACT Groundwater is a vital water source for human consumption and irrigation. Understanding its fluoride content and health implications is crucial for water resource management. This study investigated the quaternary aquifer in Suzhou, China, collecting and analyzing 49 groundwater samples. Thermodynamic simulation, multivariate statistical analysis, and health risk assessment models were employed to determine fluoride concentration characteristics, hydrochemical controlling mechanisms, and noncarcinogenic risks. Results revealed an average fluoride concentration of 0.89 mg/L, with 26.5% of samples exceeding the Grade III groundwater quality standard. High-fluoride groundwater (&amp;gt;1 mg/L) exhibited spatial heterogeneity and was predominantly of the Na-Mg-HCO3 hydrochemical type. Multivariate analysis and thermodynamics simulations indicated that water–rock interactions (e.g., silicate mineral weathering and fluorite dissolution) governed groundwater hydrochemistry. Fluoride primarily originated from fluoride-bearing mineral dissolution, while negative cation exchange and precipitation of calcite and dolomite enhanced fluoride enrichment. pH had minimal impact on fluoride concentrations under weakly alkaline conditions. Health risk assessment suggested that fluoride in shallow groundwater posed a higher noncarcinogenic risk to children than adults via ingestion. These findings provide valuable insights for regional groundwater resource management.

Formation of a Large Cold Groundwater Mantle Helium Anomaly and High Temperature Geothermal Resources in Response to Bimodal Magmatism Near Roosevelt Hot Springs and Utah FORGE, Milford Valley, Southwest Utah

AbstractA large mantle helium anomaly and separate domains of high heat flow are the predominant manifestations of bimodal magmatic activity in the Milford valley. The mantle helium anomaly (1.9–2.6 R/Ra) covers 270 km2 and is subdivided into two separated domains: a cold shallow groundwater regime and high temperature hydrothermal activity. The zone of anomalous heat flow covers &gt;100 km2 and is also subdivided into two adjacent domains, comprising hydrothermal activity at Roosevelt Hot Springs (RHS) (3–7 W/m2) and conductive heat flow (100–180 mW/m2). While the transfer of heat and mantle helium at RHS are coupled, heat and helium transfer are decoupled in the adjacent cold groundwater regime to the west. Both the mantle helium and geothermal anomalies are attributed to recent mafic‐felsic magmatic intrusions of &gt;400 km3, however, the absence of volcanic eruptions &lt;500,000 years indicates magmas stall before rising to shallow crustal level &lt;10 km depth. Deep level magmatism produces a felsic composition melt, which is inferred to be responsible for the widespread and near uniform range of diluted mantle helium values. A thick and impermeable mass of crystalline granitic basement rock at the mid‐crustal level divides the ascent of mantle helium into separate flow paths. It may also impede the rise of buoyant magma trapping thermal energy that facilitates partial melting, slow cooling, and development of a thick thermal aureole. Partitioning of convective and conductive thermal regimes and independent flow paths supplying deeply derived helium characterize the development of a large long‐lived magma‐related geothermal system.

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.

Iraqi Meteoric Water Line and its Application in Groundwater-Surface Water Connection

The LMWL was re-plotted from the isotopic analysis data (δ2H and δ18O) for rainwater samples collected from three stations in Baghdad city in the current study and data from previous studies. Four samples of shallow groundwater and five samples from the Tigris River were isotopically analyzed for 2H and 18O using a Liquid-Water Stable Isotope Analyzer (LWSIA). The samples were collected from the Al-Jaderia area within the University of Baghdad. The analysis was done against Vienna Standard Main Oceanic Water (VSMOW). The isotopic composition of groundwater ranges between -43.91‰ and -37.57 ‰ for 2H with an average of -40.06±2.7 ‰, while it ranges between -6.28‰ and -6.01‰ for 18O with an average of -6.14±0.1‰. These values are slightly more depleted compared to the isotopic composition of the Tigris River water (-38.79 ‰ to -37.87 ‰) for 2H with an average of -38.05±0.9‰ and between -6.23‰ to -5.11 ‰ for 18O with an average of -5.74±0.4 ‰. This is a logical result since the river is usually fed with fresh new rainwater, which isotopically is relatively more enriched. The current study confirms that the Local Meteoric Water Line (LMWL) has a formula of δ 2H‰ = 7.5 δ 18O‰ + 13. The LMWL is located above the Global MWL by +13.9‰ toward the Eastern Mediterranean (EMMWL δ2H‰ = 8 δ 18O‰ + 22), indicating the origin rainwater from the Mediterranean Sea and the Atlantic Ocean. The groundwater and surface water isotopic compositions were below the LMWL due to the evaporation of shallow groundwater. There is interconnection between river water and groundwater, directly or by recharge from irrigation water. Iraq may have two different MWLs, one for the northeastern region and the other for the middle, western and southern Iraq. The MWL for the northern eastern region of Iraq is close to that of the EMMWL, indicating Mediterranean climate and vapor source, while the rest of the areas of Iraq have MWL with various isotopic compositions affected by more hot climate in these regions and by the continental tropical air masses.