Changes In Groundwater Chemistry Research Articles

Geochemical Characteristics and Controlling Factors of Groundwater Chemical Composition in the Zihe River Source Area, Shandong, China

The geochemical characterization and evolution of shallow groundwater in the Zihe River source area is a key issue that needs to be addressed. In this study, a combination of traditional geochemical techniques and geochemical modeling was used to explain the geochemical processes and major ion sources in the chemical evolution of shallow groundwater in the Zihe River source area, Northeast China. Fifty-seven water samples were collected in June 2020 for chemical analysis, and the results showed that the main groundwater chemistry types in the three major aquifers are HCO3·SO4-Ca·Mg-type pore water from loose quaternary rocks, HCO3·SO4-Ca·Mg-type karstic fissure water from carbonate rocks, and HCO3·SO4-Ca-type weathered fissure water from massive rocks. Water–rock interactions in alkaline environments were the main causes of changes in groundwater chemistry. Rock weathering dominated the geochemical evolution of each aquifer. The analysis of ion concentration ratios and modeling revealed that the aquifer’s chemical components are mainly derived from the dissolution of dolomite and calcite and partly from the infiltration of pollutants containing Cl− and NO3−, as well as from the dissolution of quartz. Mg2+ is derived from the dissolution of dolomite. HCO3− is primarily derived from the co-dissolution of calcite and dolomite, and to a lesser extent, its content is also influenced by the recharge of rainfall. SO42− has two sources: it mainly originates from the dissolution of gypsum and the anhydrite layer, followed by atmospheric precipitation. The synthesis showed that the groundwater quality in the source area of Zihe River is good, all the indices reached the standard of class III groundwater quality, and the overall degree of human pollution is low. The results of this research will provide a scientific basis for the local authorities to delineate karst groundwater protection zones in the Zihe River source area and to formulate resource management strategies for the development, utilization, and protection of karst groundwater.

Observations of Decadal-Scale Brine Geochemical Change at the Bonneville Salt Flats

Over the past century, the Bonneville Salt Flats, which lies on the western edge of the Great Salt Lake watershed, has experienced changing environmental conditions and a unique history of land use, including resource extraction and recreation. The perennial halite salt crust has decreased in thickness since at least 1960. An experimental restoration project to return mined solutes began in 1997, but it has not resulted in anticipated salt crust growth. Here, primary observations of the Bonneville Salt Flats surface and subsurface brine chemistry and water levels collected from 2013 to 2023 are reported. Spatial and temporal patterns in chemistry, focused on density and water stable isotopes, are evaluated and compared with observations across seven periods of research spanning from 1925 to 2023. Declining salinity in the areas to the east of extraction ditches and south of Interstate 80 were observed. Brine extracted for potash production decreased in salinity as extraction rates increased. Between the years 1964 and 1997, the salinity of the shallow aquifer brine located beneath and to the east of the crust experienced a decrease. However, following this period, the salinity stabilized and subsequently increased. Salinity recovery was concurrent with declines in brine extraction and the salt restoration project, with the largest decrease in brine extraction being concurrent with the largest recovery in salinity. The specific impact of the restoration project on the brine salinity increase remains unclear. To the west, the shallow aquifer in the area between the Silver Island Mountains and the salt crust has increased in salinity. This increase is accompanied by a decline in groundwater levels, which enables the underground movement of solutes from east to west, following a salinity gradient away from the saline pan. Over the past 25 years, the alluvial-fan aquifer along the Silver Island Mountains has markedly declined, leading to increasingly more saline and isotopically heavier basinal waters to be extracted for industrial use. This change is concurrent with the onset of the salt restoration project, which relies on alluvial-fan aquifer waters. This compilation of changes in groundwater chemistry provides an important resource for stakeholders working to understand and manage this dynamic and ephemeral evaporite system. It also offers an example of decadal-scale change in a highly managed Great Salt Lake watershed saline system.

Application of statistics to correlate groundwater chemistry with land use on O'ahu, Hawai'i.

This study compiles commonly available groundwater chemistry data from the Pearl Harbor Sole Source Aquifer (SSA), Hawai'i-O'ahu's primary drinking water source-and applies hierarchical clustering analysis (HCA), principal component analyses (PCA), piper diagrams, and box plots with geospatial analysis to better define groundwater regions and correlate groundwater chemistry in those regions with land use. Groundwater in this aquifer recharges and flows through chemically similar soil and rocks, such that anthropogenic activities are a primary influence on the chemical variability of the aquifer's differing regions. Our analyses link specific chemical species in groundwater to land use/cover categories: urban, agriculture, and natural and anthropogenically-induced saline water intrusion. To create distinct statistical groupings with different groundwater chemistry compositions, it was important that the suite of parameters used in the statistical analysis do not covary. In our case, Cl- covaried with several major ions; however, by including F-, alkalinity, and SiOx that do not covary with Cl- in the covariance matrix, we produced improved spatial grouping of HCA clusters and stronger affinities to land use designations. Results show that dominant groundwater chemistry changes with land use along flow paths. These results pertain to areas where groundwater flows from conservation land in high recharge areas of O'ahu's mountain ranges to urban and agricultural land use regions: groundwater retains its source characteristics until about 3-6km into agricultural and urban zoned lands. Ultimately, this study outlines a simple method for water quality regulators to use groundwater chemistry to identify risks of target contaminants based on land use.

Geochemical characterisation and geostatistical evaluation of groundwater suitability: a case study in Perambalur District, Tamil Nadu, India

Groundwater is a naturally occurring potential source for drinking, irrigation, agricultural and industrial purposes. The population growth and accelerated development of industries and agriculture activity degrade groundwater quality. The groundwater quality of an area was determined by the physical and chemical parameters, influenced by geology, soil, land use, land cover and anthropogenic activities. Perambalur district in Tamil Nadu has been selected as a study area with a total geographical area of around 1757 km2. In the study area, groundwater quality decreases due to the usage of chemical fertilisers and pesticides in agricultural land and miningactivities. So, the hydrogeochemical assessment will help to determine the groundwater suitability for drinking. Forty-eight groundwater samples were collected from the study area during the pre-monsoon (July 2021) and post-monsoon season (January 2022). Samples were analysed using the standard methods prescribed by the American Public Health Association for pH, electrical conductivity (EC), total dissolved solids (TDS), calcium, magnesium, sodium, potassium, carbonate, bicarbonate, chloride, sulphate, nitrate and fluoride. The spatial distribution of major physiochemical parameters is mapped using the inverse distance weighted (IDW) interpolation technique. The evaluation of hydrochemical facies from piper plots revealed that the major cation and anion were in the order of Ca2+  > Mg2+  > Na+  > K+ and Cl-  > HCO3-  > SO42-  > NO3- in both seasons, respectively. Further, the plot explains the presence of both permanent and temporary hardness in the groundwater. The evaluation of hydrochemical facies from the piper plot emphasises that the reverse ion exchange controls groundwater chemistry. The assessment of chloro-alkaline indices reveals that the sodium and potassium in groundwater get substituted with magnesium and calcium in the parent rock, which determines the groundwater composition. The values of saturation indices reveal that calcite and dolomite are supersaturated and tend to precipitate. From principal component analysis, the principal components have an eigenvalue of more than 1, containing 79.8% and 79.2% in the total variance in pre-monsoon and post-monsoon, respectively. Most physiochemical parameters like TDS, EC, Na+, Mg2+, Cl- and SO42 - have strong positive loading and are responsible for the changes in groundwater chemistry. Finally, the calculation of the water quality index identified that groundwater quality in post-monsoon tends to decline compared to pre-monsoon.

Groundwater characterization of the eastern Minesing Wetlands in support of the endangered Hine’s emerald dragonfly (Somatochlora hineana)

The Minesing Wetlands contain Canada’s only known population of Hine’s emerald dragonfly (HED), a species listed as endangered since 2011. The HED relies on groundwater discharge areas to complete its life cycle and therefore the population is potentially sensitive to changes in groundwater. The goals of this study were to, (1) characterize groundwater discharge to the eastern portion of the Minesing Wetlands, which corresponds to the HED habitat, (2) document any significant changes in groundwater chemistry since a 1998 study, and (3) establish a comprehensive baseline water quality data set to facilitate future comparisons. Consistent with HED habitats in the USA, the chemistry of Minesing Wetlands groundwater was dominated by calcium and bicarbonate. Low groundwater chloride and nitrate concentrations indicated minimal impact from activities such as road salt application and fertilizer use. Nitrate was generally only found at the wetland margin where groundwater springs emerged from the base of the uplands. The dominant form of inorganic nitrogen in wetland groundwater was ammonium (max = 1.5 mg N/L), and soluble reactive phosphorus concentrations were also relatively high (8 to 122 µg/L). The most consistent change in wetland groundwater chemistry between the 1998 study and samples collected in 2015–2017 was that chloride concentrations in 10 of 23 wells increased over time, however the maximum mean well chloride (11.6 mg/L) remained well below the guideline for the protection of aquatic life (120 mg/L). To preserve HED habitat, potential impacts to groundwater need to be considered during land use planning for the recharge area.

Hydrochemical and stable isotopes (δ2H and δ18O) changes of groundwater from a spring induced by local earthquakes, Northwest China

It has been well reported that earthquakes can cause changes in groundwater chemistry and isotopes, and much of those changes were occurred in wells or hot springs; however, changes in cold spring caused by local small earthquakes have received less attention. Here, we collected continuous monitoring of the X10 spring (September 2018 to December 2019), investigated the hydrogeochemical characteristics of the spring by using water chemistry analysis and isotope methods. We compared the changes in water chemical ion concentrations and hydrogen-oxygen isotope ratios with the surrounding seismic activity, and the results show that 1) major chemical ion concentrations in X10 springs have an annual dynamic pattern of being high in winter and low in summer, and this change may be related to the seasonal effect of snowmelt; 2) the spring water originates from long-distant meteoric water, snowmelt, and bedrock fissure water and is affected by rock weathering and evaporation; 3) the hydrogen and oxygen stable isotope ratios and HCO3− concentration in groundwater are sensitive to local small seismic activity. We considered that small earthquakes can change the permeability in fault zones or aquifers, leading to mixing of groundwater with different chemical composition and isotopes. Our study demonstrates that the hydrogen and oxygen stable isotopes are more sensitive to seismic activity than the commonly used chemical constitutents, and that the sensitive constitutents vary in different observation wells or springs; therefore, combined monitoring of isotopes and water chemistry should be considered in the future to capture hydrogeochemical precursor signals caused by earthquakes.

Assessing Groundwater Evolution with a Combined Approach of Hydrogeochemical Modelling and Data Analysis: Application to the Rhodope Coastal Aquifer (NE Greece)

Assessing the hydrogeochemical evolution of groundwater is a challenging task, which is further exacerbated when considering the multiple geogenic and anthropogenic impacts that affect its quality and the hydraulic interactions between different aquifer bodies. This study combined hydrogeochemical modelling and data analysis to assess this complex hydrogeological regime. Before modelling, the groundwater samples were clustered using a multivariate statistical method (hierarchical cluster analysis (HCA)). Then, the Geochemist Workbench (GWB) software was applied to model the hydrogeochemical groundwater evolution, including the dominant ion exchange process, and to explain the changes in groundwater chemistry towards its flow. The input data consisted of five key parameters from seventy-seven sampling points collected in two periods (accounting for the start and the end of the irrigation period). A data analytical approach based on the optimal mixing ratios between the interacting groundwater systems and recharge inputs was also performed as part of the methodological approach. It revealed a progressively temporal-dependent behaviour of the aquifer system during the irrigation period, resulting in seasonal changes in the hydrodynamic conditions and depletion of the upper aquifer layers. Specifically, the aquifer system was confirmed to undergo cation exchange as the dominant geochemical process that increases calcium concentrations. The complex hydrogeological regime was further evaluated by assessing the mixing ratios of the different aquifer layers. Hence, the aquifer system (bulk samples) was mixed with the irrigation water by 71% and 97% and with the lateral recharge by 76% and 29% for the beginning and at the end of the irrigation period, respectively. Overall, the joint assessments were confirmed by the hydrogeochemical status of the end-members and the modelling approach and explained the sequential changes in groundwater chemistry due to the dominant ion-exchange process and the mixing of different water bodies. The proposed methodological approach proved that it could be used as an exploratory and preliminary method for capturing the temporal dynamics in complex groundwater systems and supporting groundwater resource management.

Aquifer recharge by stormwater infiltration basins: Hydrological and vadose zone characteristics control the impacts of basins on groundwater chemistry and microbiology

Stormwater infiltration systems (SIS) are designed to collect and infiltrate urban stormwater runoff into the ground for flood risk mitigation and artificial aquifer recharge. Many studies have demonstrated that infiltration practices can impact groundwater chemistry and microbiology. However, quantitative assessments of the hydrogeological factors responsible of these changes remain scarce. Thus, the present study aimed to quantitatively test whether changes of groundwater chemistry and microbiology induced by SIS were linked to two factors associated with vadose zone properties (vadose zone thickness, water transit time from surface to groundwater) and one factor associated with groundwater recharge rate (assessed by groundwater table elevation during rain events). To evaluate changes in chemistry (NO3−, PO43− and dissolved organic carbon concentrations), groundwater samples were collected in wells located in SIS-impacted and non-SIS-impacted zones during experimental periods of 10 days. During the same periods, clay beads were incubated in the same wells to measure changes of groundwater microbial biofilms (microbial biomass, dehydrogenase and hydrolytic activities) induced by SIS. Results showed that changes in PO43− supplied to groundwater during stormwater infiltration was negatively correlated with vadose zone thickness. A short water transit time from surface to groundwater increased dissolved organic carbon concentrations in the aquifer which, in turn, increased biofilm biomasses in groundwater. The groundwater recharge rate during rain events (assessed by groundwater table elevation) diluted NO3− concentrations in the aquifer but also influenced the changes of biofilm activities induced by SIS. Groundwater recharge rate during rain events probably increased the fluxes of water and dissolved organic carbon in groundwater, stimulating the activity of microbial biofilms. Overall, the present study is the first to quantify conjointly several factors and processes (water transfer, dilution, solute fluxes) that could explain the impact of stormwater infiltration on chemistry and/or microbiology in groundwater.

Vertical nitrate migration and denitrification zones in a regional recharge area (Lwówek region, Poland)

We examine the influence of groundwater flow patterns and denitrification on nitrate migration in a regional recharge zone. It has been shown that nitrate contamination has a different behaviour in regions where groundwater is exploited (where deep percolation of nitrate takes place) than where natural gradients exist (with no deep aquifer zone contamination). Multicomponent chemical tracers and isotopic methods were used in the investigation. A contaminant plume was discovered in shallow parts of the aquifer which percolated into deeper parts of the flow system in those regions with a downwards gradient induced by groundwater withdrawal, where the influence of denitrification was limited. Local conditions leading to intense denitrification, i.e., local changes in geological conditions (low-permeability silt intercalations), were also documented. Therefore, vertical changes in groundwater chemistry should be examined to ensure groundwater resource management and protection, as these are extremely important in regional recharge zones with a downwards gradient.

Estimation of groundwater pollution levels and specific ionic sources in the groundwater, using a comprehensive approach of geochemical ratios, pollution index of groundwater, unmix model and land use/land cover – A case study

This study aimed to evaluate the degree of groundwater pollution and to assess the contribution of specific ionic sources to groundwater, thereby helping to identify the changes in groundwater chemistry and also in groundwater quality from a rural part of Telangana, India, using the comprehensive understanding of geochemical ratios (GR), pollution index of groundwater (PIG), unmix model (UM), and land use/land cover. Groundwater samples collected (22) from the study area were analysed for pH, EC, TDS, Ca2+, Mg2+, Na+, K+, HCO3−, Cl−, SO42−, NO3−, and F−. The hydrogeochemical diagram showed the dominant groundwater type of Ca2+- Mg2+- HCO3− due to the water-soil-rock interactions. GR, chloro-alkaline indices, and saturation indices revealed the groundwater chemistry that explains the mineral weathering and dissolution, ion exchange, and evaporation processes as the chief geogenic origin, and also the contamination of surface water due to the influence of household wastewater, septic tank leaks, irrigation-return-flows, chemical composts, etc. as the secondary anthropogenic sources on the aquifer system. Changes in groundwater quality from the recharge area to the discharge area and the correlation coefficient of chemical variables further supported the sources of geogenic and anthropogenic origins. According to PIG's calculations, the present study area was classified as the insignificant pollution zone (5.89%), which shows all chemical variables within their drinking water quality limits, and the low pollution zone (43.34%), medium pollution zone (27.48%), high pollution zone (17.34%), and very high pollution zone (5.95%), which exhibit the TDS, Mg2+, Na+, K+, HCO3−, Cl−, NO3−, SO42−, and F−contents above the drinking water quality standards. This indicates the gradual increase in the intensity of pollution activity. UM also classified the contribution of specific ions (>50%) into three sources: Source I (K+) measures the poor sewage conditions and potash fertilizers; Source II (SO42−, Mg2+, NO3−, Na+, and Ca2+) specifies the poor sewage conditions, irrigation-return-flows, and chemical fertilizers (gypsum and nitrate); and Source III (F− and HCO3−) represents the dissolution of fluoride minerals as a major contributor to groundwater chemistry. Furthermore, the land use/land cover observations had also supported the assessment of groundwater pollution levels and the contribution of specific ionic sources made by PIG and UM. As a result, the present study clearly indicated that groundwater quality of a geogenic origin is primarily overcome the impact of anthropogenic sources. Therefore, the present study suggested strategic measures to control groundwater pollution and improve groundwater quality.

Vertical stratification of microbial communities and isotope geochemistry tie groundwater denitrification to sampling location within a nitrate-contaminated aquifer

Nitrate pollution is a major threat to groundwater quality in agricultural areas. Natural attenuation of nitrate in contaminated aquifers is mediated by denitrifying microbial populations in anoxic environments. Vertical distribution of denitrifying microbial communities in aquifers is greatly influenced by groundwater redox conditions, local hydrogeological parameters, and seasonal variability in groundwater flow and recharge. In this study, we investigated groundwater geochemistry and the composition of bacterial and archaeal communities with increasing depth in a shallow nitrate-contaminated aquifer in British Columbia, Canada. High-resolution passive diffusion sampling was conducted to collect groundwater at 10-cm intervals from 4 to 20 m below ground surface (mbgs) in the aquifer. Geochemical analyses of major ions indicated a general shift in the groundwater chemistry below 16 mbgs including decreasing chloride concentrations that suggest two-end member mixing of shallow and deep groundwater with different chemistries. A redoxcline was further observed within a 2 m transition zone at 18–20 mbgs characterized by sharp declines in nitrate concentrations and increases in sulfate and total inorganic carbon. Excursions in δ15N-NO3− and δ18O-NO3− in the same depth interval are consistent with denitrification, and a concomitant decrease in δ34S-SO42− suggested that denitrification was coupled to sulfide or sulfur oxidation. Microbial communities within this depth interval were significantly dissimilar to those above and below, featuring putative lithotrophic denitrifying bacteria belonging to the genera Sulfurifustis, Sulfuritalea and Sulfuricella. These lineages were detected in greatest abundance at 19 mbgs while the abundances of putative heterotrophic sulfate-reducing bacteria belonging to the genus Desulfosporosinus were greatest at 20 mbgs. In addition to help distinguish denitrification from mixing-induced changes in groundwater chemistry, the above observed vertical stratification of the microbial key players connects nitrate removal to the locations of the aquifer sampled.

Hydrochemical peculiarities and groundwater quality assessment of the Birimian and Tarkwaian aquifer systems in Bosome Freho District and Bekwai Municipality of the Ashanti Region, Ghana

The Birimian and Tarkwaian aquifer systems are the main sources of water supply for the Bosome Freho District and Bekwai Municipality inhabitants in the Ashanti region of Ghana. A hydrogeochemical assessment was carried out to ascertain the natural baseline chemistry of the groundwaters and the factors influencing groundwater chemistry in these two areas. A multivariate statistical tool consisting of principal component analysis (PCA) and hierarchical cluster analysis (HCA) together with hydrochemical graphical plots was applied on 64 groundwater samples. The Q–mode HCA results were used to explain the changes in groundwater chemistry along the flow paths where three spatial groundwater zones and water types were delineated. The first type consists of Ca–Mg–HCO3 freshwater (recharge zone), which transitions into Ca–Na–HCO3 or Na–Ca–HCO3 mixed waters (intermediate zone) and finally evolves to the third type of Na–Ca–Mg–HCO3–Cl water (discharge zone). The study also reveals that the natural process influencing water chemistry is groundwater–rock interaction from carbonate and silicate weathering/dissolution, aided by carbonic acid from precipitation and releases concentration of Na+, Ca2+, Mg2+, and HCO3− into the groundwaters significantly. The chloro-alkaline indices also reveal cation exchange as the principal natural factor that controls groundwater chemistry in the area. Inverse geochemical modelling shows the dissolution of primary minerals such as dolomite, plagioclase, halite, gypsum, and precipitation of calcite and chlorite along the groundwater flow path. Anthropogenic activities have little influence on groundwater chemistry. The quality of groundwater in the Bosome Freho District and Bekwai Municipality is suitable for irrigational use and drinking water consumption. The results obtained so far will contribute to research paucity in the study area and serve as a guide for decision-makers for improved water resources management.

Appraisal of shallow groundwater quality with human health risk assessment in different seasons in rural areas of the Guanzhong Plain (China)

Groundwater is the major source of water for drinking and irrigation purposes in and around Hua County, Shaanxi Province, China. The main purposes of this research is to evaluate the groundwater quality in the rainy and dry seasons of Hua County and analyze the causes of seasonal differences and determine the areas with serious pollution. Groundwater quality was assessed in this study using entropy water quality index (EWQI) and some graphical approaches such as Gibbs and Piper diagrams. The contour maps of groundwater quality were drawn by Geographical Information System (GIS). According to the obtained results, the locations where groundwater quality was rated as excellent or good in both wet and dry seasons were mainly in the north and east of the research area. COD and NO3− are the parameters that have the most serious negative effect on water quality. The dominant factors influencing groundwater chemical evolution in the study area were rock weathering and dissolution, and the precipitation and evaporation during the wet and dry seasons do not cause significant changes in groundwater chemistry. Adults' health risks results revealed that 27.69% and 52.31% of the groundwater samples exceeded the acceptable limit for non-carcinogenic risk in the wet and dry season, respectively, while for children the ratios are 30.16% and 47.62%, respectively. The contributive percentages of nitrate, fluoride and nitrate to the total risk are 61.29%, 28.71% and 10.00% in the wet season and 68.84%, 20.85% and 10.31% in the dry season. The risk is higher in the south than in the north of the study area, and is especially high in the southwest of the study area.

Geo-Chemical Techniques for Earthquake Forecasting in Nigeria

Regardless of the doubt caused by some rounds on the impossibility of earthquake forecast, more and more countries, even at the highest governmental levels, realize that doing nothing is the ostrich position of dread before the real difficulties associated with the creation of a real forecasting system. Nigeria in times past was believed to be aseismic. However, the seismic record of Nigeria from 1933-2021 have demonstrated in contrast to the idea, numerous quakes have been recorded in Nigeria throughout the years. With the development of observation techniques and theoretical knowledge of geochemistry, geochemical observation of faults gas has become a hotspot once more in recent years. Rn, Hg, H2, etc., are used for geochemical observations. 222Rn has a half-life of 3.825 days, a magnitude 5.0 earthquake will be detected through precursory phenomena at a distance not greater than 142 km. Mercury and other elements are used as important detectors for earthquake prediction and they play an important role in revealing the relationship between fluid in the fault zone and the occurrence of earthquakes, the range for a magnitude 5.0 earthquake is limited to 200 km. Hydrogen concentrations have been monitored for precursory variations in many fault systems, using either discrete sampling and laboratory analysis or continuous monitoring of ground gas, using hydrogen-sensitive fuel cells. Precursory changes in groundwater chemistry are often attributed to the mixing of fluids from two or more chemically distinct aquifers, the physical mechanism responsible for the mixing of fluids is, however, not well established.

Groundwater Chemistry and Stratification in the Flooded Hard-Coal Mine Shaft “Nowy I” (Nowa Ruda Region, SW Poland)

The flooding of unprofitable underground mines is one of the methods of their closure. After the drainage of the mine has stopped, the voids left in the rock mass as a result of mining, are filled with inflowing groundwater. In this way, reservoirs of groundwater with specific physicochemical parameters are formed. These parameters depend on the interaction of the water flowing into the workings with the rock formations. It was the economic situation in the 1990s that led to the closure of hard coal mines in the Nowa Ruda Coal Basin, where the flooded “Nowy I” shaft is located. In that shaft, in 2008, hydrogeological research was performed and groundwater samples from five various depths were collected. The aim of the study was to recognize if groundwater stratification occurs in the shaft. In 2015, a sample of the water outflowing through the “Aleksander” adit was taken to check the potential influence of mine flooding on the environment and to confirm the changes in groundwater chemistry over time. These were the first, and so far, the only studies on the chemical composition of water in the flooded mine in that area. The article presents results of the preliminary research, which confirmed the existence of not obvious hydrogeochemical stratification in the shaft. It can be assumed that below the depth of 350 m, the water circulating through mining excavations exhibits the highest electrical conductivity and the highest concentration of Ca2+, K+, SO42−, Fetot. In the depth range of 320–380 m there is a transition zone, in which a decrease of Eh value and a change of reduction and oxidation is recorded. Above this zone, infiltration water inflow, from outside the shaft casing, dominates. The research shows that it would be necessary to perform additional sampling of the water in the shaft at greater depths, as well as to perform isotope analysis and periodical tests for at least several years. This would allow for a more complete characterisation of hydrogeochemical processes taking place in the flooded mine.

Variaciones geomorfológicas como condicionantes de la química del agua subterránea en el litoral del estuario medio del Río de la Plata

El objetivo del trabajo es determinar los cambios en la química del agua subterránea y los procesos geoquímicos asociados en función de las variaciones geomorfológicas en el ámbito de la planicie costera del Río de la Plata en el sector litoral del estuario medio. Para ello se estableció una red de monitoreo que involucra puntos de muestreo de agua superficial y subterránea donde se determinó el contenido de iones mayoritarios, nitrato e isótopos estables de la molécula de agua. El contenido en isótopos ambientales registra, para el caso del agua subterránea, que el agua de lluvia infiltra sin previa evaporación y recarga al agua subterránea somera. Las muestras de agua superficial presentan porcentajes de evaporación menores al 10%. Estos bajos porcentajes pueden deberse a que el muestreo se realizó en un mes de excesos hídricos. En cuanto al contenido de iones mayoritarios se registran variaciones en función de la geomorfología. Así, la antigua llanura intermareal y la planicie con cordones de conchilla presentan facies que varían según la profundidad del muestreo entre bicarbonatada sódica y clorurada sódica. Estas variaciones estarían controladas por la composición original del agua meteórica y las reacciones químicas producto de la interacción con el sedimento. Particularmente, la química del agua subterránea de la marisma está regulada por los flujos mareales provenientes del Río de la Plata.

Groundwater Throughflow and Seawater Intrusion in High Quality Coastal Aquifers

High quality coastal aquifer systems provide vast quantities of potable groundwater for millions of people worldwide. Managing this setting has economic and environmental consequences. Specific knowledge of the dynamic relationship between fresh terrestrial groundwater discharging to the ocean and seawater intrusion is necessary. We present multi- disciplinary research that assesses the relationships between groundwater throughflow and seawater intrusion. This combines numerical simulation, geophysics, and analysis of more than 30 years of data from a seawater intrusion monitoring site. The monitoring wells are set in a shallow karstic aquifer system located along the southwest coast of Western Australia, where hundreds of gigalitres of fresh groundwater flow into the ocean annually. There is clear evidence for seawater intrusion along this coastal margin. We demonstrate how hydraulic anisotropy will impact on the landward extent of seawater for a given groundwater throughflow. Our examples show how the distance between the ocean and the seawater interface toe can shrink by over 100% after increasing the rotation angle of hydraulic conductivity anisotropy when compared to a homogeneous aquifer. We observe extreme variability in the properties of the shallow aquifer from ground penetrating radar, hand samples, and hydraulic parameters estimated from field measurements. This motived us to complete numerical experiments with sets of spatially correlated random hydraulic conductivity fields, representative of karstic aquifers. The hydraulic conductivity proximal to the zone of submarine groundwater discharge is shown to be significant in determining the overall geometry and landward extent of the seawater interface. Electrical resistivity imaging (ERI) data was acquired and assessed for its ability to recover the seawater interface. Imaging outcomes from field ERI data are compared with simulated ERI outcomes derived from transport modelling with a range of hydraulic conductivity distributions. This process allows for interpretation of the approximate geometry of the seawater interface, however recovery of an accurate resistivity distribution across the wedge and mixing zone remains challenging. We reveal extremes in groundwater velocity, particularly where fresh terrestrial groundwater discharges to the ocean, and across the seawater recirculation cell. An overarching conclusion is that conventional seawater intrusion monitoring wells may not be suitable to constrain numerical simulation of the seawater intrusion. Based on these lessons, we present future options for groundwater monitoring that are specifically designed to quantify the distribution of; (i) high vertical and horizontal pressure gradients, (ii) sharp variations in subsurface flow velocity, (iii) extremes in hydraulic properties, and (iv) rapid changes in groundwater chemistry. These extremes in parameter distribution are common in karstic aquifer systems at the transition from land to ocean. Our research provides new insights into the behaviour of groundwater in dynamic, densely populated, and ecologically sensitive coastal environments found worldwide.

Geochemical characterization of shallow groundwater using multivariate statistical analysis and geochemical modeling in an irrigated region along the upper Yellow River, Northwestern China

The geochemical characterization of groundwater in irrigated regions along the upper Yellow River is a pivotal issue to be addressed. In this study, the integration of multivariate statistical techniques and geochemical modeling was used to decipher the geochemical processes and agricultural practices affecting chemical evolution of phreatic water in a typical irrigated area along the upper Yellow River, Northwestern China. Seventy-eight water samples were collected in September 2018 for chemical analysis. Results showed that groundwater samples were classified as the low mineralized Group 1 with mixed cations-HCO3-SO4 water, and Group 2 with highly saline Na-Cl-SO4 water. Both groups were mainly distributed on both banks of the Yellow River, respectively, suggesting different recharge sources with distinct chemical compositions. Water-rock interaction in alkaline environment and nitrate contamination were mainly responsible for changes in groundwater chemistry. Rock weathering and evaporation-crystallization predominate the geochemical evolution of Group 1 and Group 2, respectively. The geochemical processes occurring in the aquifer mainly include the dissolution of halite, gypsum, Glauber's salt, fluorite, feldspars and dolomite, calcite precipitation, along with cation exchange. Nitrate contamination in the study area may be attributed to the combined effects of high-dose application of nitrogen fertilizers and the localized fine-grained zone with low permeability. Additionally, the inverse geochemical modeling showed that relative to the west bank of the Yellow River, the groundwater flow path on the east side of the Yellow River experienced larger amounts of evaporites' dissolution and cation exchange, and was more affected by the dedolomitization processes. The findings of this research not only contribute to the geochemical characterization of shallow groundwater in the irrigated area, but also provide valuable information for the authorities to formulate the strategies of groundwater sustainable management in such irrigated regions along the upper Yellow River.

Comparison of Hydrogeochemical and Geodynamic Conditions in Deep Horizons in the Central West-Siberian Megabasin

Regularities in the hydrogeochemical and geodynamic conditions were compared in the regions of the central West-Siberian megabasin, neighboring the Koltogorskaya–Tol’kinskaya suture zone. No regularities were shown to exist between the changes in groundwater chemistry and the tectonic conditions of the early period of basin development. The relatively recent or currently active tectonic processes were found to correlate with the distribution of groundwater mineralization in all aquifer systems and, partially, for individual components of ion–salt composition.

In situ observation of helium and argon release during fluid-pressure-triggered rock deformation

Temporal changes in groundwater chemistry can reveal information about the evolution of flow path connectivity during crustal deformation. Here, we report transient helium and argon concentration anomalies monitored during a series of hydraulic reservoir stimulation experiments measured with an in situ gas equilibrium membrane inlet mass spectrometer. Geodetic and seismic analyses revealed that the applied stimulation treatments led to the formation of new fractures (hydraulic fracturing) and the reactivation of natural fractures (hydraulic shearing), both of which remobilized (He, Ar)-enriched fluids trapped in the rock mass. Our results demonstrate that integrating geochemical information with geodetic and seismic data provides critical insights to understanding dynamic changes in fracture network connectivity during reservoir stimulation. The results of this study also shed light on the linkages between fluid migration, rock deformation and seismicity at the decameter scale.