Geochemical Evolution Of Groundwater Research Articles

Identifying the origin and geochemical evolution of groundwater using hydrochemistry and stable isotopes in the Subei Lake basin, Ordos energy base, Northwestern China

Abstract. A series of changes in groundwater systems caused by groundwater exploitation in energy base have been of great concern to hydrogeologists. The research aims to identify the origin and geochemical evolution of groundwater in the Subei Lake basin under the influence of human activities. Water samples were collected, and major ions and stable isotopes (δ18O, δD) were analyzed. In terms of hydrogeological conditions and the analytical results of hydrochemical data, groundwater can be classified into three types: the Quaternary groundwater, the shallow Cretaceous groundwater and the deep Cretaceous groundwater. Piper diagram and correlation analysis were used to reveal the hydrochemical characteristics of water resources. The dominant water type of the lake water was Cl-Na type, which was in accordance with hydrochemical characteristics of inland salt lakes; the predominant hydrochemical types for groundwater were HCO3–Ca, HCO3–Na and mixed HCO3–Ca–Na–Mg types. The groundwater chemistry is mainly controlled by dissolution/precipitation of anhydrite, gypsum, halite and calcite. The dedolomitization and cation exchange are also important factors. Rock weathering is confirmed to play a leading role in the mechanisms responsible for the chemical composition of groundwater. The stable isotopic values of oxygen and hydrogen in groundwater are close to the local meteoric water line, indicating that groundwater is of modern local meteoric origin. Unlike significant differences in isotopic values between shallow groundwater and deep groundwater in the Habor Lake basin, shallow Cretaceous groundwater and deep Cretaceous groundwater have similar isotopic characteristics in the Subei Lake basin. Due to the evaporation effect and dry climatic conditions, heavy isotopes are more enriched in lake water than in groundwater. The low slope of the regression line of δ18O and δD in lake water could be ascribed to a combination of mixing and evaporation under conditions of low humidity. Comparison of the regression line for δ18O and δD showed that lake water in the Subei Lake basin contains more heavily isotopic composition than that in the Habor Lake basin, indicating that lake water in the discharge area has undergone stronger evaporation than lake water in the recharge area. Hydrochemical and isotopic information of utmost importance has been provided to decision makers by the present study so that a sustainable groundwater management strategy can be designed for the Ordos energy base.

Geochemical evolution of groundwater in the Mud Lake area, Eastern Idaho, USA

Groundwater with elevated dissolved-solids concentrations—containing large concentrations of chloride, sodium, sulfate, and calcium—is present in the Mud Lake area of Eastern Idaho. The source of these solutes is unknown; however, an understanding of the geochemical sources and processes controlling their presence in groundwater in the Mud Lake area is needed to better understand the geochemical sources and processes controlling the water quality of groundwater at the Idaho National Laboratory. The geochemical sources and processes controlling the water quality of groundwater in the Mud Lake area were determined by investigating the geology, hydrology, land use, and groundwater geochemistry in the Mud Lake area, proposing sources for solutes, and testing the proposed sources through geochemical modeling with PHREEQC. Modeling indicated that sources of water to the eastern Snake River Plain aquifer were groundwater from the Beaverhead Mountains and the Camas Creek drainage basin; surface water from Medicine Lodge and Camas Creeks, Mud Lake, and irrigation water; and upward flow of geothermal water from beneath the aquifer. Mixing of groundwater with surface water or other groundwater occurred throughout the aquifer. Carbonate reactions, silicate weathering, and dissolution of evaporite minerals and fertilizer explain most of the changes in chemistry in the aquifer. Redox reactions, cation exchange, and evaporation were locally important. The source of large concentrations of chloride, sodium, sulfate, and calcium was evaporite deposits in the unsaturated zone associated with Pleistocene Lake Terreton. Large amounts of chloride, sodium, sulfate, and calcium are added to groundwater from irrigation water infiltrating through lake bed sediments containing evaporite deposits and the resultant dissolution of gypsum, halite, sylvite, and bischofite.

Investigating groundwater recharge by means of stable isotopes in the Al-Khazir Gomal Basin, northern Iraq

Stable isotopes (δ18O and δ2H), 14C and groundwater chemistry were used in this study for gaining insight into the recharge mechanisms and groundwater geochemical evolution in a semi-arid region of northern Iraq. The 3,185 km2 large catchment of the Al-Khazir Gomal Basin is divided into three regions (south, central, and north) depending on structural and geological aspects. In terms of hydrogeology, the vast syncline in the central part of the watershed is considered to be the most important region regarding groundwater quality and quantity. Groundwater samples of both confined and unconfined aquifers plot on or slightly above the local meteoric water line and the slope of the δ18O and δ2H regression line for the confined and unconfined aquifers is 7.26 and 7.01, respectively. This is interpreted as an indicator of considerable recharge with short residence time for the shallow groundwater, excluding the effect of evaporation before infiltration. This assumption was supported by low chloride concentrations, groundwater Ca-HCO3 type and the high values of 14C activities. The variations in stable isotopes and 14C in the confined aquifer support the assumption of existence of different recharge resources and mechanisms. Hydrogeochemically, there are three main mechanisms contributing to the chemical evolution of the groundwater; these are the preferential chemical weathering of the carbonate cement of the sandstones, geochemical weathering of silicate minerals and cation exchange processes. Meteoric NaCl is considered to be the main source of dissolved Na and Cl ions in freshwater samples. Additional Na might stem from cation exchange with dissolved Ca and Mg.

The impact of hydrogeological settings on geochemical evolution of groundwater in karstified limestone aquifer basin in northwest Sri Lanka

The geochemical and isotope analysis of groundwaters from the Murunkan basin in north western Sri Lanka was carried out to examine their evolution and recharge sources in order to shed light to enhance the current knowledge of the hydro-geochemical processes in a karst geological setting. A total of 40 water samples from ground and surface water bodies were collected from the Miocene limestone terrain, nearby metamorphic and from unconsolidated Quaternary terrains for major anions, cations and environmental isotopes ratios (δ18OVSMOW and δ2HVSMOW). Distinct geochemical differences were noted between waters from limestone terrain and nearby metamorphic terrain indicating the modification of groundwater flow paths. Bicarbonate-chloride rich water is dominated in the limestone terrain in which water flows through a less mineralized aquifer system and is modified by the sea water intrusion. Groundwater in the metamorphic terrain is modified by dissolving of Ca–Mg rich mineral phases and subsequent ion exchange processes. The environmental isotopes of groundwater from both limestone and metamorphic terrains vary from −0.38 to −6.68 ‰ and −2.41 to −42.3 ‰ for δ18OVSMOW and δ2HVSMOW, respectively. However, slightly enriched isotope signatures and low d-excess values from limestone terrain indicate an excessive evaporation compared to that of the metamorphic terrain where rapid infiltration occurs through the overlying highly permeable grumusols soil layers.

Hydrochemical Appraisal and Geochemical Evolution of Groundwater with Special Reference to Nitrate Contamination in Aquifers of a Semi-Arid Terrain of NW India

Hydrochemical characteristics of 85 groundwater samples collected from the semi-arid terrain of Ajmer district of Rajasthan state, India, during pre-monsoon season, indicate generally hard-to-very hard, fresh-to-brackish, alkaline and medium-to-high saline waters with the dominance of Na–Cl, Na–HCO\(_{3}\) and mixed water types. Hydrofacies and statistical analysis reveals that the dominant processes controlling the chemistry of groundwater are evaporation, salinisation, mineral precipitation and dissolution, ion exchange and anthropogenic activity. The groundwater quality is poor compared to the drinking water specifications of Bureau of Indian Standards and significant spatial variability exists in nitrate concentration. Nitrate content, high in groundwater samples of hard rock areas, shows negative correlation with well depth due to denitrification processes at higher depth. The nitrate content is also reduced with an increase in distance from ridges and pediments, particularly along rivers due to dilution effect. Domestic sewerage and industrial wastes aggravated by fertilizer inputs are responsible for nitrate contamination in the study area. Bivariate plots of ions, correlation, and factor analysis support the role of anthropogenic activities influencing the nitrate contamination of groundwater.

Geochemical processes controlling the groundwater transport of contaminants released by a dump in an arid region of México

The Vado Carranza dump, located in the Mexicali Valley, Baja California, northwest Mexico, was operated for more than 15 years receiving about 30 tons/day of solid wastes. The disposed wastes were periodically burned in open air. The presence of a shallow aquifer in the area makes the groundwater vulnerable to contamination processes. The purpose of this study was the evaluation of heavy metals content (Cu, Cd, Ni, Pb and Zn) in soil and groundwater in the vicinity of this dump. The results indicate high content of metals in soil, mainly at a superficial level, with the highest concentrations in the areas where burning of wastes occurred. Elevated concentrations of cadmium and copper were detected in groundwater with the highest concentrations occurring in monitoring wells located in the north side of the dump, downward of groundwater flow. Although the high content of metals in soil can be attributed to the burning of waste, other sources of pollution could be the agricultural irrigation in the vicinity of the dump. The program PHREEQC was used to model the geochemical evolution of groundwater. Results suggest that evaporation of the contaminated waters circulating below the landfill is one of the key processes that explain the increased concentration of contaminants in groundwater and its seasonal variations. As groundwater flows away from the dump, evaporation can concentrate the chemicals making the water more toxic. These results are important because they illustrate processes that are likely to occur in landfills located in other desert areas of the world.

Geochemical evolution of groundwater in carbonate aquifers of southern Latium region, central Italy

Spring and well water samples, from carbonate aquifers of Latium region, have been characterized to determine the hydrochemical processes governing the evolution of the groundwater. Most of the spring samples, issuing from Lepini, Ausoni and Aurunci Mts., are characterized as alkaline earth HCO3 waters, however, some samples show a composition of Cl--SO4 -- alkaline earth waters. Groundwater samples from Pontina Plain shows three different hydrochemical facies: alkaline earth HCO3 type, Cl-- SO4 -- alkaline earth type and Cl--SO4 -- alkaline type waters. Geochemical modeling and saturation index computation of the sampled waters show an interaction with calcareous and calcareous-dolomitic lithologies. Most of the springs and wells was kinetically saturated with respect to calcite and dolomite, and all the samples were below the equilibrium state with gypsum. This indicates that the groundwater has capacity to dissolve the gypsum along the flow paths. The electrical conductivity and Cl- concentrations of the sampled waters show a positive trend with the decrease in the distance from the coast, highlighting seawater intrusion in the coastal area. According to hydrochemistry results and geochemical modeling, the dominant factors in controlling the hydrochemical characteristics of groundwater are: (i) water rock interaction with calcareous and calcareous-dolomitic lithologies; (ii) seawater intrusion in the coastal area; (iii) dissolution and/or precipitation of carbonate and (i.e. dolomite and calcite) evaporate minerals (gypsum) determined by saturation indexes; (iv) mineral weathering process; (the high Mg/Ca ratio due to the weathering of Mg-rich dolomite).

Hydrogeochemical investigation in an arid region of Iran (Tabas, Central Iran)

Groundwater is the most important source of water supply in Iran and understanding the geochemical evolution of groundwater is important for sustainable development of the water resources in Tabas area. A total of 29 samples of groundwater in Tabas area have been analyzed for ions and major elements. Groundwater of the study area is characterized by the dominance of Na–Cl water type. Groundwater was generally acidic to high alkaline with pH ranging from 5.42 to 10.75. The TDS as a function of mineralization characteristics of the groundwater ranged from 479 to 10,957 mg/l, with a mean value of 2,759 mg/l. The Ca2+, Mg2+, SO42− and HCO3− were mainly derived from the dissolution of calcite, dolomite and gypsum. The Cu, Pb and Zn ions are not mobile in recent pH–Eh, but these conditions controlled dissolved Se, V and Mo in groundwater. The As is released in groundwater as a result of the weathering of sulfide minerals like arsenopyrite.

Geochemical evolution of groundwater in the unsaturated zone of a karstic massif, using the [formula omitted] relationship

Summary In karstic environments, groundwater is strongly influenced by CO 2 partial pressure variations of air present in the infiltration zone of these aquifers. In order to characterize the geochemical changes in groundwater as it moves through the infiltration zone, we monitored various rising springs in the perched karstic aquifer of Cussac (Dordogne, France), and measured the CO 2 partial pressure in air of a nearby cavity (the Cussac Cave) for 24 months. Our method is based on the relationship between the saturation index with respect to calcite (SIc) and the CO 2 partial pressure at atmospheric equilibrium with water. We distinguished a value for this last parameter when water is at equilibrium with respect to calcite (SIc = 0) called saturation CO 2 partial pressure. The use of this parameter can provide information on flow conditions and relationships between water, air, and rock. Cussac aquifer is a suitable area to apply these methods because of its small size, numerous springs, and a cave that provides data for CO 2 partial pressure condition inside the massif. Results show that most of the calcium-carbonate mineralization is acquired in the epikarst followed by a precipitation phase in the upper part of the infiltration zone. Groundwater reaches the saturated zone with some degree of saturation depending on CO 2 partial pressure variations in air inside the massif.

Geochemical Evolution of Groundwater in Meng Xu Area, Gui Ping City, Southern China

Geochemical data on dissolved major constituents in groundwater samples from Meng Xu area reveal the main processes responsible for their geochemical evolution. Inverse models were developed using PHREEQC to elucidate the chemical reactions controlling water chemistry. The inverse modeling demonstrated that relatively few phases are required to derive water chemistry in the area. In a broad sense, the reactions responsible for the hydro chemical evolution in the area fall into four categories: dissolution of CO2; calcite dissolution; incongruent dolomite dissolution, dedolomization, ex-solution of CO2, and ion exchange. Apart from this process, there are others which influence the geochemical zoning of the system. The interaction of the CO2 with the carbonate matrix of the aquifer produces an increase in the alkalinity of the water.

Geochemical evolution of groundwater in carbonate aquifers in Taiyuan, northern China

Thirty-nine samples of both cold and thermal karst groundwater from Taiyuan, northern China were collected and analyzed with the aim of developing a better understanding of the geochemical processes that control the groundwater quality evolution in the region’s carbonate aquifers. The region’s karst groundwater system was divided into three geologically distinct sub-systems, namely, the Xishan Mountain karst groundwater subsystem (XMK), the Dongshan Mountain karst groundwater subsystem (DMK) and the Beishan Mountain karst groundwater subsystem (BMK). Hydrochemical properties of the karst groundwaters evolve from the recharge zones towards the cold water discharge zones and further towards the thermal water discharge zones. In the XMK and the DMK, the hydrochemical type of the groundwater evolves from HCO3–Ca·Mg in the recharge – flow-through zone, to HCO3·SO4–Ca·Mg/SO4·HCO3–Ca·Mg in the cold water discharge zone, and further to SO4–Ca·Mg in the thermal water discharge zone. By contrast, the water type changes from HCO3–Ca·Mg to HCO3·SO4–Ca·Mg in the BMK, with almost invariable TDS and temperatures all along from the recharge to the discharge zone. The concentrations of Sr, Si, Fe, F− and of some trace elements (Al, B, Li, Mn, Mo, Co, Ni) increase as groundwater temperature increases. Different hydrogeochemical processes occur in the three karst groundwater sub-systems. In the XMK and the DMK, the geochemical evolution of the groundwater is jointly controlled by carbonate dissolution/precipitation, gypsum dissolution and dedolomitization, while only calcite and dolomite dissolution/precipitation occurs in the BMK without dedolomitization. The hydrogeochemical data of the karst groundwaters were used to construct individual geochemical reaction models for each of the three different karst groundwater sub-systems. The modeling results confirm that dedolomization is the major process controlling hydrochemical changes in the XMK and the DMK. In the thermal groundwaters, the dissolution rates of fluorite, siderite and strontianite were found to exceed those of the cold karst groundwater systems, which can explain the higher concentrations of F−, Fe and Sr2+ that are found in these waters.

Isotopic and geochemical evidence of recharge sources and water quality in the Quaternary aquifer beneath Jinchang city, NW China

Multiple isotopic and hydrogeochemical tracers were utilized to understand the recharge sources and geochemical evolution of groundwater in the Quaternary aquifer beneath Jinchang city and the adjacent Gobi desert area. The groundwater shows markedly depleted stable isotopic composition compared to modern rainfall. The signature of groundwaters from Jinchang and the northern Gobi desert area differ clearly from that of the alluvial fan in the south Yongchang basin and modern rainfall, and has lower or non-detectable (3)H activity, implying that the aquifer is likely maintained by palaeowater. This groundwater in the Gobi desert has a (14)C age older than 12 ka, indicating that the groundwater resources are non-renewable. The build-up of dissolved solids through evaporation is a major control on groundwater composition, and the dominant anion species change systematically from HCO(3)(-), SO(4)(2-) to Cl(-), but cations from weathering of albite, calcite, dolomite and gypsum also make a significant contribution. The scientific results have important implications for groundwater management in Jinchang city and as well as in the Shiyang River basin under China's West Development Strategy. It is recommended that the water allocation program of diverting water from the Dongda river to the Minqin basin be reconsidered. (C) 2010 Elsevier Ltd. All rights reserved.

Evaluation of hydrogeochemical processes in arsenic-contaminated alluvial aquifers in parts of Mid-Ganga Basin, Bihar, Eastern India

The study region covers 1,650 km2 of the Mid-Ganga Basin in Bihar, experiencing intensive groundwater draft. The area forms a part of the Gangetic alluvial plain where high incidence of arsenic groundwater contamination (>50 μg/l) has recently been detected. Seventy-seven groundwater samples have been collected and analysed for major ions, iron and arsenic. Arsenic contamination (max 620 μg/l) is confined in hand pump zones (15–35 m) within the newer alluvium deposited during Middle Holocene to Recent age. The older alluvial aquifers are arsenic-safe and recorded maximum concentration as 9 μg/l. Out of 12 hydrochemical facies identified, four have been found arsenic-affected: Ca–HCO3, Mg–HCO3, Ca–Mg–HCO3 and Mg–Ca–HCO3. The geochemical evolution of groundwater, as investigated by graphical interpretation and statistical techniques (correlation, principal component analysis) revealed that dissolution of detrital calcite, dolomite and infiltration of rainwater are the major processes shaping the groundwater chemistry in the newer alluvium. Arsenic and iron showed strong positive correlation. Rainfall infiltration, carrying organic matter from recently accumulated biomass from this flood-prone belt, plays a critical role in releasing arsenic and iron present in the sediments. Geochemical evolution of groundwater in older alluvium follows a different path, where cation-exchange has been identified as a significant process.

Groundwater geochemical evolution in the northern portion of the Guarani Aquifer System (Brazil) and its relationship to diagenetic features

The groundwater flow pattern in the northern portion of GAS (Guarani Aquifer System) is characterized by the existence of four regional recharge areas located in São Paulo, Mato Grosso do Sul and Goiás states. From these areas of recharge the regional flow is radial and directed toward the center of the Paraná Sedimentary Basin. Local discharge occurs in portions of outcrop regions. The groundwater has low mineralization and can be classified as Ca or Ca–Mg–HCO3 type, Na–HCO3 type and Na–HCO3/Cl/SO4 type, this sequence represents the hydrochemical evolution. The mechanisms responsible for this evolution are dissolution of feldspars and removal of the carbonate cement from the sandstone mineral framework, followed by ion exchange, responsible for the increase in the Na concentration and decrease of Ca, and, finally, enrichment in Cl and SO4 derived from underlying aquifer units. The hydrochemical evolution is consistent with diagenetic features that are observed in the sandstones, with the presence of siliceous cement in the outcrop areas, and carbonate cement toward the center of Paraná Basin.

Geochemical evolution of groundwater in the Cambrian–Vendian aquifer system of the Baltic Basin

The shallowly buried marginal part of the Cambrian–Vendian confined aquifer system of the Baltic Basin is characterised by fresh and low δ 18O composition water, whereas the deeply settled parts of the aquifer are characterized by typical Na–Ca–Cl basinal brines. Spatial variation in water geochemistry and stable isotope composition suggests mixing origin of the diluted water of three end-members—glacial melt water of the Weichselian Ice Age (115 000–10 000 BP), Na–Ca–Cl composition basin brine and modern meteoric water. The mixing has occurred in two stages. First, the intrusion and mixing of isotopically depleted glacial waters with basinal brines occurred during the Pleistocene glacial periods when the subglacial melt-water with high hydraulic gradient penetrated into the aquifer. The second stage of mixing takes place nowadays by intrusion of meteoric waters. The freshened water at the northern margin of the basin has acquired a partial equilibrium with the weakly cemented rock matrix of the aquifer.

Geochemical evolution of groundwater in the carbonate aquifers of Sierra de Segura (Betic Cordillera, southern Spain)

Sierra de Segura (Betic Cordillera), with a total area of over 3000 km2, is the source of the two principal rivers in southern Spain, the Guadalquivir and the Segura. Due to the orographic effect of these mountains, precipitations are considerably more abundant than in nearby lowland areas, where the climate is semi-arid. Sierra de Segura is constituted of Mesozoic and Cenozoic sedimentary rocks, among which there are thick limestone–dolomitic formations which have given rise to extensive outcrops of permeable materials. In geomorphological terms, there is a large plateau intensively karstified that constitutes the main recharge area. Discharge takes place via a large number of springs, of which the 50 most important add up to a mean spring flow of about 13,500 l/s. The active geochemical processes in aquifers of Sierra de Segura, with their corresponding time sequence, are: dissolution of CO2, dissolution of calcite, incongruent dissolution of dolomite, dedolomitization, exsolution of CO2, and precipitation of calcite. More evolved water has higher temperature, magnesium content and Mg/Ca ratio; therefore, these parameters can be utilised as indicators of the degree of hydrochemical evolution. In addition, a good correlation between water temperature and magnesium concentration (or Mg/Ca ratio) indicates that an increase in temperature accelerates the kinetics of the dissolution of dolomite. Finally, the distribution of the temperatures in the vadose zone, determined by atmospheric thermal gradient, implies an apparent stratification of the predominant hydrochemical processes and of the groundwater physical and chemical characteristics.

Geochemical evolution of groundwaters in the Michigan and Appalachian basins, southwestern Ontario

Geochemical evolution of groundwaters in the Michigan and Appalachian basins, southwestern Ontario

Paleowaters in Silurian-Devonian carbonate aquifers: Geochemical evolution of groundwater in the Great Lakes region since the Late Pleistocene

Changes in the climatic conditions during the Late Quaternary and Holocene greatly impacted the hydrology and geochemical evolution of groundwaters in the Great Lakes region. Increased hydraulic gradients from melting of kilometer-thick Pleistocene ice sheets reorganized regional-scale groundwater flow in Paleozoic aquifers in underlying intracratonic basins. Here, we present new elemental and isotopic analyses of 134 groundwaters from Silurian-Devonian carbonate and overlying glacial drift aquifers, along the margins of the Illinois and Michigan basins, to evaluate the paleohydrology, age distribution, and geochemical evolution of confined aquifer systems. This study significantly extends the spatial coverage of previously published groundwaters in carbonate and drift aquifers across the Midcontinent region, and extends into deeper portions of the Illinois and Michigan basins, focused on the freshwater–saline water mixing zones. In addition, the hydrogeochemical data from Silurian-Devonian aquifers were integrated with deeper basinal fluids, and brines in Upper Devonian black shales and underlying Cambrian-Ordovician aquifers to reveal a regionally extensive recharge system of Pleistocene-age waters in glaciated sedimentary basins. Elemental and isotope geochemistry of confined groundwaters in Silurian-Devonian carbonate and glacial drift aquifers show that they have been extensively altered by incongruent dissolution of carbonate minerals, dissolution of halite and anhydrite, cation exchange, microbial processes, and mixing with basinal brines. Carbon isotope values of dissolved inorganic carbon (DIC) range from −10 to −2‰, 87Sr/ 86Sr ratios range from 0.7080 to 0.7090, and δ 34 S – SO 4 values range from +10 to 30‰. A few waters have elevated δ 13C DIC values (>15‰) from microbial methanogenesis in adjacent organic-rich Upper Devonian shales. Radiocarbon ages and δ 18O and δD values of confined groundwaters indicate they originated as subglacial recharge beneath the Laurentide Ice Sheet (14–50 ka BP, −15 to −13‰ δ 18O). These paleowaters are isolated from shallow flow systems in overlying glacial drift aquifers by lake-bed clays and/or shales. The presence of isotopically depleted waters in Paleozoic aquifers at relatively shallow depths illustrates the importance of continental glaciation on regional-scale groundwater flow. Modern groundwater flow in the Great Lakes region is primarily restricted to shallow unconfined glacial drift aquifers. Recharge waters in Silurian-Devonian and unconfined drift aquifers have δ 18O values within the range of Holocene precipitation: −11 to −8‰ and −7 to −4.5‰ for northern Michigan and northern Indiana/Ohio, respectively. Carbon and Sr isotope systematics indicate shallow groundwaters evolved through congruent dissolution of carbonate minerals under open and closed system conditions ( δ 13C DIC = −14.7 to−11.1‰ and 87Sr/ 86Sr = 0.7080–0.7103). The distinct elemental and isotope geochemistry of Pleistocene- versus Holocene-age waters further confirms that surficial flow systems are out of contact with the deeper basinal-scale flow systems. These results provide improved understanding of the effects of past climate change on groundwater flow and geochemical processes, which are important for determining the sustainability of present-day water resources and stability of saline fluids in sedimentary basins.

Origin and geochemical evolution of groundwaters from Lastochka spa (Primorye, Russia)

Origin and geochemical evolution of groundwaters from Lastochka spa (Primorye, Russia)

Recharge areas and geochemical evolution of groundwater in an alluvial aquifer system in the Sultanate of Oman

A regional hydrogeochemical model was developed to evaluate the geochemical evolution of different groundwaters in an alluvial aquifer system in the Interior of Oman. In combination with environmental isotopes the model is able to extract qualitative and quantitative information about recharge, groundwater flow paths and hydraulic connections between different aquifers. The main source of water to the alluvial aquifer along the flow paths of Wadi Abyadh and Wadi M’uaydin in the piedmont is groundwater from the high-altitude areas of the Jabal Akhdar and local infiltration along the wadi channels. In contrast, the piedmont alluvial aquifer along Wadi Halfayn is primarily replenished by lateral recharge from the ophiolite foothills to the east besides smaller contributions from the Jabal Akhdar and local infiltration. Further down gradient in the Southern Alluvial Plain aquifer a significant source of recharge is direct infiltration of rain and surface runoff, originating from a moisture source that approaches Oman from the south. The model shows that the main geochemical evolution of the alluvial groundwaters occurs along the flow path from the piedmont to the Southern Alluvial Plain, where dedolomitization is responsible for the observed changes in the chemical and carbon isotope composition in these waters.