Source Of Recharge Research Articles

Hydrogeological and remote sensing investigation of the fractured carbonate aquifer, East El Minia, Eastern Desert, Egypt

Groundwater resources in the Sahara are the backbone of the sustainable agricultural development. However, the assessment of groundwater dynamics, particularly the role of structural control on groundwater flow and recharge mechanism in Saharan karst aquifers (KA) is poorly constrained due to sparse hydrological data. The KA in East El-Minia area (EMA), in the Eastern Desert of Egypt is highly affected by a set of major faults related to the post-Eocene tectonics and Red Sea rifting system. The present study integrates field observations, Phased Array type L-band Synthetic Aperture Radar images (PALSAR), digital elevations models, geophysical, stable isotope and geochemical data to identify the structural control on groundwater flow and the recharge mechanisms in the KA. Analysis of the PALSAR data indicated that the area was affected by a set of NW trending normal faults and related grabens while the aeromagnetic data showed consistency of subsurface faults with the surficial trend. Isotopic data of groundwater from the KA indicated two mixing groups with three recharge sources. Group I, groundwater samples with mixed isotopic signature between Nubian Sandstone paleo-water and modern meteoric water with slightly depleted isotopic signature (δ18O: 3.2‰ to - 1.22‰, δ2H: 18.55‰ to - 1.44‰).Group II, mixed water signatures between the old and modern Nile water endmembers with slightly enriched signatures (δ18O: 0.02‰–0.55‰, δ2H: 4.91‰ to 27.03‰).Finally, mass balance calculations indicated that the mixing in Group I is dominated by Nubian-paleowater and rainwater, while in Group II samples are dominated by Nile water which indicates that NW faults control the recharge from the Nile at El Sareiryia watershed while impeding the recharge from the Nile at El Tahnwia. Our findings shed light on the role of structural control on groundwater dynamics in the KA in arid regions.

Application of a Linked Hydrodynamic–Groundwater Model for Accurate Groundwater Simulation in Floodplain Areas: A Case Study of Irtysh River, China

The rich biodiversity in the floodplain area is influenced by both floodplain floods and groundwater (GW). To protect the ecological environment in the floodplain area, it is essential to study the interaction between floodplain floods and GW. The objective of this paper is to propose a coupling strategy between a hydrodynamic model and a GW model to provide an accurate simulation tool for quantifying the interaction between floodplain floods and GW. The case study is conducted in the floodplain area of the middle reaches of the Irtysh River in northwest China. Firstly, a two-dimensional hydrodynamic model based on TELEMAC-2D is constructed to accurately simulate floodplain floods under wetting and drying conditions. Secondly, a GW model based on MODFLOW is developed. Finally, a coupling strategy is proposed to achieve accurate and efficient integration between the hydrodynamic model and the GW model. The calibration and verification results of the model demonstrate high accuracy, with root mean squared error (RMSE) values of 0.51 m and 0.77 m between observed and calculated GW levels for the hydrodynamic–GW coupled model. The water balance results indicate that floodplain floods serve as the largest GW recharge source in the study area, while phreatic evaporation is the primary GW discharge item. This paper represents a novel attempt to couple a two-dimensional hydrodynamic model with a GW model. The research results provide a scientific tool for the ecological restoration of floodplain areas considering both surface water and GW, as well as the comprehensive management and regulation of wetland water resources and the water environment.

Thermokarst lakes group accelerates permafrost degradation in the Qinghai–Tibet Plateau, China: A modeling study

Thermokarst lakes in the Qinghai–Tibet Plateau (QTP) are increasing in number and lake surface area, intensifying the lake–permafrost interaction and making it more complex, thus affecting the hydrological and ecological environment. Although the impact of the individual lake on permafrost has been studied, the effects of lakes group on permafrost and regional hydrological processes remain unexplored. Hence, in this study, modified SUTRA models considering thermal conduction and convection processes were established for five scenarios, including a current environment and four thought experiments, to determine whether and how thermokarst lakes group accelerates permafrost degradation. The models could effectively simulate the variations in the ground temperature with time and depth, with the highest RMSE and lowest R2 being 1.443 °C and 0.706, respectively. Thermal conduction and convection played a dominant role before and after the formation of through-taliks below the thermokarst lakes, respectively. Through-taliks strengthened the hydraulic connection between supra-permafrost water, sub-permafrost water, and lakes, and changed the groundwater circulation pattern. An increase in the number of thermokarst lakes led to the formation of more through-taliks and improved the heat transfer efficiency, accelerating permafrost degradation. Thermal erosion of the permafrost base was more severe in the presence of a recharge source and pathway via a talik. The results highlight the importance of thermal convection and groundwater circulation in permafrost degradation. The findings can help understand the interaction mechanism between permafrost and thermokarst lakes and the variation in environmental and eco-hydrological processes in cold regions.

Hydrochemical and isotopic characteristics of the Lodwar Alluvial Aquifer System (LAAS) in Northwestern Kenya and implications for sustainable groundwater use in dryland urban areas

Groundwater is a crucial resource for dryland regions such as this, where surface water resources are limited and unreliable. This paper presents a study of the Lodwar Alluvial Aquifer System (LAAS) in northwestern Kenya and its hydrochemical and isotopic characteristics, with the goal of understanding how to sustainably manage the groundwater system. As a result, the paper focuses on elucidating the hydrogeochemical and river-groundwater interaction (using environmental isotopes and major ion chemistry) of an aquifer that is located in the north-western dryland of Kenya. The study utilised environmental isotopes of oxygen-18 (18O), deuterium (2H), and tritium (3H) as tracers for establishing recharge sources and origin of groundwater. A sampling campaign involving 112 water samples was conducted to establish isotopic compositions of rain, spring, surface water (rivers, scoop holes, dams and lake) and groundwater at the peak of the wet season in May 2018. The tritium values in the study area ranged from 1.1 to 2.4 TU. Considering the median values of δ18O and δ2H in surface water and groundwater samples, four clusters emerge based on the degree of enrichment; Cluster 1 comprises the lake water (δ18O = +6.01, δ2H = +41.9); Cluster 2 is the Turkwel and Kawalase river water with slightly positive relative to VSMOW and with different δ2H values (+7.6‰ versus −9.8‰). The third cluster is the groundwater of the Shallow Alluvial Aquifer (SAA) and the Deep Aquifer (DA) (δ18O = −0.96‰ and −0.70‰; and δ2H = +0.4‰ and +0.6‰, respectively). The last cluster comprises the most isotope-depleted waters of water pans, scoop holes, Intermediate Aquifer (IA) and Turkana Grit Shall Aquifer (TGSA) with median values ranging from −2.87‰ to −2.48‰ for δ18O and −8.6‰ and −16.4‰ for δ2H. While the SAA is mainly recharge by the Turkwel River, a relationship is observed between the values deuterium in the Kawalase (−9.6‰ VSMOW) and IA (−8.6‰ VSMOW). Understanding recharge sources and aquifer vulnerability of similar strategic aquifers helps scientists appropriately advise policymakers and the water community who develop sustainable water use, aquifer protection and conservation strategies. In addition, the study contributes scientific evidence of isotopic compositions of groundwater in the Horn of Africa. Furthermore, the evidence of surface water-groundwater interaction presents a case of a fragile dryland ecosystem. Future work will involve the installation of piezometers in strategic aquifer zones to monitor groundwater levels in relation to river gauging data to quantify the amount of recharge and establish the impacts of rainfall variability in the upstream catchment.

Effects of recharge process on groundwater nitrate concentration in an oasis of Tengger Desert hinterland, China.

Groundwater nitrate concentrations cannot be effectively diluted in an oasis of desert hinterland without direct recharge from external rivers. Therefore, there is an urgent need to understand the relationship between groundwater nitrate concentration and the groundwater recharge process. Using hydrochemicals, stable isotopes, LUCC, and combining these with the MixSIAR model, the distributions of groundwater nitrate concentration in the Dengmaying Basin (DMYB) in 2006 and 2020 were obtained. The contributions of groundwater recharge and nitrate sources were also quantified. With the development of agriculture in the DMYB, groundwater irrigation leakage has gradually become a crucial recharge source of groundwater, with a recharge proportion reaching 30.3%. From 2006 to 2020, under the influence of well irrigation and agricultural fertilization, the groundwater nitrate concentration in the DMYB increased significantly, with an increased range of 1.3 ~ 14.3mg L-1. Moreover, the δ15N-NO3- and δ18O-NO3- values of nitrate in cultivated soil water were similar to those in groundwater, which also proves the process of carrying nitrate from the vadose zone into groundwater by irrigation water. The contribution of anthropogenic sources (54.9%) to groundwater nitrate exceeded that of natural sources (45.1%) to groundwater nitrate in the DMYB. These results indicate that the potential for nitrate pollution in groundwater must be considered, even in desert oases.

Estimating groundwater recharge and precipitation sources of the Zamora River Basin, southeastern Ecuador, using GIS and stable isotopes

Estimating groundwater recharge and precipitation sources of the Zamora River Basin, southeastern Ecuador, using GIS and stable isotopes

Mechanisms of water-rock interaction and implications for remediating flooded mine workings elucidated from environmental tracers, stable isotopes, and rare earth elements

Contamination from acid mine drainage affects ecosystems and usability of groundwater for domestic and municipal purposes. The Captain Jack Superfund Site outside of Ward, Boulder County, Colorado, USA, hosts a draining mine adit that was remediated through emplacement of a hydraulic bulkhead to preclude acid mine drainage from entering nearby Lefthand Creek. During impoundment of water within the mine workings in 2020, a diverse and novel dataset of stable isotopes of water, sulfate, and carbon (δ2H, δ18OH2O, δ18OSO4, δ34S, δ13CDIC), rare earth elements, and environmental tracers (noble gases and tritium) were collected to understand groundwater recharge and mixing, mechanisms of sulfide oxidation and water-rock interaction, and the influence of remediation on the hydrologic and geochemical system. Water isotopes indicate that groundwater distal from the mine workings has seasonally variable recharge sources whereas water within the workings has a distinctive composition with minimal temporal variability. Sulfate isotopes indicate that sulfide oxidation occurs both within the mine workings and in adjacent igneous dikes, and that sulfide oxidation may occur under suboxic conditions with ferric iron as the oxidant. Carbon isotopes track the neutralization of acidic waters and the carbon mass budget of the system. Rare earth elements corroborate stable isotopes in indicating groundwater compartmentalization, and additionally illustrate enhanced mineral weathering in the mine workings. Environmental tracers indicate mixing of modern and pre-modern groundwater and inform timelines that active remediation may be needed. Together these datasets provide a useful template for similar investigations of abandoned mine sites where physical mixing processes, sources of solute loading, or remediation timeframes are of importance.

Machine learning model predicting hydrothermal dolomitisation for future coupling of basin modelling and geochemical simulations

In the energy transition context, basin modelling, initially dedicated to the understanding of oil and gas systems, can address several challenges that the sustainable energy sector faces, such as identifying large storage volumes for carbon sequestration, determining the thermal recharge sources for geothermal exploration, or characterising the generation, migration, sink, and accumulation of critical element resources. In this regard, there is a need for spatiotemporal information on the mineral reactions that control the petrophysical properties of the rocks in order to map the best locations in the basin for capturing geothermal energy or storing carbon in basin-wide reservoirs for CO2 mitigation. Hydrothermal dolomitisation is one of these well-known diagenetic reactions that can enhance or destroy reservoir porosity. It has been extensively characterised by static reactive transport modelling, but not kinematic ones, due to the high computational cost of such reactive transport simulations. To address this issue, we built a machine-learning-based (ML) surrogate geochemical model for hydrothermal dolomitisation valid over a broad range of physical and chemical conditions encountered in such a context with the end goal of developing a generic exploration tool to be deployed in the basin calculator ArcTem for emerging energy needs. We train and test five regression algorithms (Random Forest, Gradient Boosting, AdaBoost, Support-Vector Machine, and Multilayer Perceptron) upon a synthetic dataset to predict the dissolved/precipitated amount of calcite and dolomite (referred to as δCaCO3 and δCaMg(CO3)2, respectively). The dataset contains 370 × 103 samples and six features (T, pH, NaCl, Ca, Mg, C) generated by a Latin Hypercube Sampling (LHS) between two end-members: (1) the modern seawater composition and a temperature of 80 °C for the lower bound and (2) a highly saline mantle-derived fluid and a temperature of 250 °C for the upper bound. The target values, i.e. dissolved/precipitated mole number of calcite/dolomite, are obtained by performing thermodynamic equilibrium calculations with the LHS samples as the initial unequilibrated solutions. Our results show that the artificial neural network (ANN) model best performs among the algorithms with rmse of 0.007 mol on δCaMg(CO3)2 prediction and 0.0084 mol on δCaCO3 prediction, R2 values above 0.99, and APE smaller than 0.3%, indicating its good generalisability to provide accurate predictions on unseen data in the studied range. Further, the ANN model is ∼1000 times faster than the geochemical calculator when solving the same system at once, illustrating the great potential of ML methods in emulating computationally intensive components of the numerical simulations.

Spatial Variation Characteristics, Influencing Factors, and Sources of Hydrogeochemical of Surface Water and Groundwater in Mountainous Area of Hutuo River

Surface runoff has dropped sharply in the mountainous area of the Hutuo River, posing a huge challenge to the sustainable use of groundwater in the North China Plain (NCP). The Taihang Mountain area is the main recharge source area of groundwater in the NCP. An in-depth study of spatial variation characteristics, influencing factors, and sources of hydrogeochemical characteristics of surface water and groundwater in the mountainous area of the Hutuo River can facilitate a comprehensive understanding of regional water resource status and sustainable utilization of water resources. Based on isotopic, hydrogeochemical, and mathematical statistics methods, this study analyzed spatial variation of hydrochemical characteristics in surface water and groundwater and its sources and main controlling factors. The results showed that the river water, well water, and spring water were all recharged by atmospheric precipitation in the mountainous areas of the Hutuo River. Under the combined influence of natural factors and human factors, the hydrogeochemical characteristics of river, well, and spring water showed large spatial differences. On the whole, the hydrochemical types of mainstreams were relatively concentrated. In the upper and lower mining reach areas, the mainstream water chemical type was dominated by Ca·Mg-SO4·HCO3, whereas that in the natural vegetation area (middle reach:between Qingshui River and Longhua River) was dominated by Ca·Mg-HCO3·SO4. In the upper stream, the main hydrochemical type of the Yukou River and Ehe River tributaries was Ca·Mg-SO4·HCO3, which was consistent with that of the main stream. The main hydrochemical types of the Muma River and Qingshui River tributaries were Ca-HCO3, Ca·Mg-HCO3, and Ca·Mg-HCO3·SO4 in the midstream. The main hydrochemical types of the Mianhe River and Yehe River tributaries were Ca-SO4, Ca·Mg-SO4, and Ca·Mg-SO4·HCO3. Mineral dissolution was still the main controlling factor for the hydrochemical characteristics of surface water and groundwater in the mountainous area of the Hutuo River. The contribution rates were 69.86% and 18.84% for mineral dissolution and human activities, respectively. Therefore, in the future, water resource utilization in the upper reaches of the Hutuo River should not only consider the issue of water quantity but also a series of water environment problems such as nitrate pollution and mining pollution caused by human activities.

Mapping regional and nested flow systems in the karst aquifers of Jinan spring using hydrochemical and isotope data

Abstract This study enhances the understanding of the evolution of water transport in karst water flow systems. This paper explores the karst water flow system from a hydrogeochemical perspective. It has been discovered that in the recharge area, the hydrochemical effect of karst water is primarily influenced by dissolution and filtration. In the fault zone and concentrated discharge area, it is primarily influenced by mixing. In the geothermal area, the dominant factors are dissolution, precipitation, and dolomitization. From the southern to the northern area, the hydrochemical type of karst water gradually changes from HCO3-Ca type to SO4·Cl-Ca·Na type. Atmospheric precipitation is the primary recharge source of karst water, with a recharge elevation range of 181–1,495 m. According to geological drilling statistics, the groundwater transport depth transits from the shallow transport in the south to the deep transport in the north, with a depth range of 3,000–3,500 m, and using isotope data to obtain the groundwater retention time range is 6–27,000 years. The groundwater transport mode is divided into three levels: open-shallow transport karst cold water phreatic flow, semi-open-medium-deep transport karst cold water confined flow, and weak open-deep transport geothermal water confined water flow.

Water budget study for groundwater recharge in Indus River Basin, Punjab (Pakistan)

Abstract Assessing groundwater recharge is crucial for managing and governing water resources in any region. Indus River Basin (IRB) is an area that relies heavily on canal and groundwater irrigation. The replenishment of groundwater is largely dependent on surface water supplies. The purpose of this research is to determine the amount of groundwater recharge from various sources in Rachna Doab. The study employed the water budget method to calculate seasonal groundwater recharge during the Rabi (October–March) and Kharif (April–September) (Summer) periods from 2005 to 2011. The main components of the recharge were rainfall, water conveyed through channels, and irrigation water applied to cultivated fields. Conversely, the extraction of water from private and public tube wells was the discharge component of the study. Groundwater levels increased during the Kharif season but decreased during the Rabi season. Average recharge contribution from rainfall was 45 and 14% during the Kharif and Rabi seasons, respectively. The total annual recharge from watercourses and irrigation fields was estimated to be approximately 33% of the total recharge. Rainfall was the most significant source of long-term seasonal recharge, followed by watercourses and irrigation fields. In general, the average depletion of the reservoir was 94 million cubic meters per season.

Unveiling recharge sources and dominant processes for alluvial aquifers using hydrochemical and isotopic techniques

The study deals with the hydrochemistry (EC, DO, pH, HCO3–, SO2-4, Cl−, Ca2+, Mg+, Na+, and K+) and isotopic studies (18O, 2H, and 3H) of the groundwater of the Thal Doab, between River Indus and Jhelum, to delineate the sources of recharge and quality of groundwater. The groundwater based on isotopic data is recharged by two sources: the Indus River and rainfall shown by the depleted and enriched isotopic concentrations. The tritium concentrations revealed the short residence time of shallow groundwater as compared to the deeper groundwater. Furthermore, a deep groundwater upwelling zone has also been identified. Furthermore, it was found that the groundwater evolved in response to rock–water interaction, evaporation, precipitation, land use changes, and other anthropogenic activities. The groundwater system in the Chashma area is relatively safe for consumption. Future planning for the groundwater recharge zones should be the priority areas for protection, by the government water management and public health departments.

Managing coastal aquifer salinity under sea level rise using rice cultivation recharge for sustainable land cover

Study regionThe coastal aquifer of Nile Delta, Egypt is used to develop the current study. Study focusExcess water from rice irrigation is a source of incidental recharge to mitigate seawater intrusion. This paper numerically explores the optimal location of rice cultivations by subdividing the delta domain into three distinct recharging regions (north, central and south). Additionally, SEAWAT code was simulated under a combination of rice cultivation relocation and sea level rise (SLR). New hydrological insights for the regionThe study findings revealed significant variations in salt volume reduction depending on the location of rice cultivation in the delta. Placing rice cultivation in the northern region resulted in the highest reduction of salt volume (19 %). In contrast, locating the recharge in the central region yielded a salt volume reduction of 0.50 %, while rice cultivation in the southern region produced a 15 % increase. Considering the projected SLR of 61 cm by 2100, there was an overall salt volume increment of 3 %. However, when accounting for both SLR and rice cultivation recharge in the northern region, a substantial salt volume reduction of 17 % was observed. The results demonstrated that incidental recharge by rice cultivation in coastal aquifers is an effective method for enhancing saltwater intrusion control. Moreover, this study improves our understanding of hydrological processes and expected responses in the delta under future climate scenarios.

The genesis of an extremely acidic perched aquifer within roasted pyrite waste in a fully urbanized area (Zaragoza, Spain)

Contaminated groundwater is a serious problem in developed countries. The abandonment of industrial waste may lead to acid drainage affecting groundwater and severely impacting the environment and urban infrastructure. We examined the hydrogeology and hydrochemistry of an urban area in Almozara (Zaragoza, Spain); built over an old industrial zone, with pyrite roasting waste deposits, there were acid drainage problems in underground car parks. Drilling and piezometer construction, and groundwater samples revealed the existence of a perched aquifer within old sulfide mill tailings, where the building basements interrupted groundwater flow, leading to a water stagnation zone that reached extreme acidity values (pH < 2). A groundwater flow reactive transport model was developed using PHAST to reproduce flow and groundwater chemistry, in order to be used as a predictive tool for guiding remediation actions. The model reproduced the measured groundwater chemistry by simulating the kinetically controlled pyrite and portlandite dissolution. The model predicts that an extreme acidity front (pH < 2), coincident with the Fe (III) pyrite oxidation mechanism taking dominance, is propagating by 30 m/year if constant flow is assumed. The incomplete dissolution of residual pyrite (up to 18 % dissolved) predicted by the model indicates that the acid drainage is limited by the flow regime rather than sulfide availability. The installation of additional water collectors between the recharge source and the stagnation zone has been proposed, together with periodic pumping of the stagnation zone. The study findings are expected to serve as a useful background for the assessment of acid drainage in urban areas, since urbanization of old industrial land is rapidly increasing worldwide.

Assessment of the interactions between soil–biosphere–atmosphere (ISBA) land surface model soil hydrology, using four closed-form soil water relationships and several lysimeters

Abstract. Soil water drainage is the main source of groundwater recharge and river flow. It is therefore a key process for water resource management. In this study, we evaluate the soil hydrology and the soil water drainage, simulated by the interactions between soil–biosphere–atmosphere (ISBA) land surface model currently used for hydrological applications from the watershed scale to the global scale, where parameters are generally not calibrated. This evaluation is done using seven lysimeters from two long-term model approach sites measuring hourly water dynamics between 2009 and 2019 in northeastern France. These 2 m depth lysimeters are filled with different soil types and are either maintained as bare soil or covered with vegetation. Four closed-form equations describing soil water retention and hydraulic conductivity functions are tested, namely the commonly used equations from Brooks and Corey (1966) and van Genuchten (1980), a combination of the van Genuchten (1980) soil water retention function with the Brooks and Corey (1966) unsaturated hydraulic conductivity function, and, for the very first time in a land surface model (LSM), a modified version of the van Genuchten (1980) equations, with a new hydraulic conductivity curve proposed by Iden et al. (2015). The results indicate good performance by ISBA with the different closure equations in terms of soil volumetric water content and water mass. The drained flow at the bottom of the lysimeter is well simulated, using Brooks and Corey (1966), while some weaknesses appear with van Genuchten (1980) due to the abrupt shape near the saturation of its hydraulic conductivity function. The mixed form or the new van Genuchten (1980) hydraulic conductivity function from Iden et al. (2015) allows the solving of this problem and even improves the simulation of the drainage dynamic, especially for intense drainage events. The study also highlights the importance of the vertical heterogeneity of the soil hydrodynamic parameters to correctly simulate the drainage dynamic, in addition to the primary influence of the parameters characterizing the shape of the soil water retention function.

Occurrence, source identification and ecological risk assessment of heavy metals in water and sediments of Uchalli lake – Ramsar site, Pakistan

Uchalli Lake is an internationally significant Ramsar site that needs protection for supporting migratory birds. The current study aimed to assess wetland health by examining water and sediments utilizing total and labile heavy metals concentration, pollution indices, ecological risk assessment, water recharge and pollution induction sources through isotope tracer techniques. Al concentration in water was of serious concern as it was 440 times higher than the maximum acceptable concentration of Environmental Quality Standard of the UK for aquatic life in saline waters. Labile concentration predicted very severe enrichment of Cd, Pb, and moderate enrichment of Cu. Modified ecological risk index predicted very high ecological risk in sediments. The δ 18O, δ2H and D-excess values indicate that the lake was mainly recharged by local meteoric water. Enriched values of δ 18O and δ2H suggest a high evaporation of lake water, making lake sediments more enriched with metals. Isotopic and D-excess values of groundwater suggest a quick rainwater recharge to groundwater around the Uchalli Lake. Nitrates isotopes indicate that the rainwater runoff is main source of induction of fertilizers, pesticides and soil bonded metals in the lake system. The lake is recharged by rainwater runoff, from catchment areas, that erode the soil particles and agricultural residual waste dumped in the lake.

Coupling hydrogeochemistry and stable isotopes (δ2H, δ18O and δ13C) to identify factors affecting arsenic enrichment of surface water and groundwater in Precambrian sedimentary rocks, eastern salt range, Punjab, Pakistan.

The study area is a part of the Salt Range, where water quality is being deteriorated by natural and anthropogenic sources. This research integrates water quality assessment, arsenic enrichment, hydrogeochemical processes, groundwater recharge and carbon sources in aquifer. Total dissolved solid (TDS) contents in springs water, lake water and groundwater are in range of 681-847mg/L, 2460-5051mg/L and 513-7491mg/L, respectively. The higher concentrations of magnesium and calcium in water bodies next to sodium are because of carbonates, sulfates, halite and silicates dissolution. The average concentrations of ions in groundwater are in order of HCO3- > SO42- > Cl- > Na+ > Mg2+ > Ca2+ > K+ > NO3-, virtually analogous to springs water, but different from lake water, categorized as poor quality and unfit for drinking purposes. Based on major ions hydrochemistry, NaCl and mixed Ca-Mg-Cl type hydrochemical facies are associated with concentration of arsenic (4.2-39.5µg/L) in groundwater. Groundwater samples (70%) having arsenic concentration (11 ≤ As ≤ 39.5µg/L) exceeded from World Health Organization (WHO) guideline (As ≤ 10µg/L) in near neutral to slightly alkaline (6.7 ≤ pH ≤ 8.3), positive Eh(6 ≤ Eh ≤ 204mV), signifying its oxic condition. Eh-pH diagrams for arsenic and iron indicate that 80% of groundwater for arsenic and iron were in compartments of HAsO42- and Fe(OH)3, unveil oxic environment. Arsenic is moderately positive correlated with TDS, sodium, chloride, bicarbonate, nitrate, sulfate and weak negative with δ13CDIC in surface and groundwater, forecasting multiple sources of arsenic to aquifer. Stable isotopes of waters show recharge of groundwater from local rain and lake water. The lower δ13CDIC values of groundwater are modified by influx of CO2 produced during biological oxidation of soil natural organic matter.

Groundwater Pollution Risk Assessment in Plain Area of the Yarkant River Basin

Groundwater pollution risk assessment is an effective method to manage groundwater resources and prevent groundwater pollution. The DRSTIW model was used to evaluate the groundwater vulnerability in a plain area of the Yarkant River Basin, and factor analysis was used to identify pollution sources for pollution loading evaluation. The functional value of groundwater was estimated by considering both the mining value and the in-situ value. The entropy weight method and the analytic hierarchy process (AHP) were used to determine the comprehensive weight, and a groundwater pollution risk map was generated based on the overlay function of ArcGIS software. The results showed that the natural geological factors such as large groundwater recharge modulus, wide recharge sources, strong permeability of soil surface and unsaturated zone, and shallow groundwater depth facilitated pollutant migration and enrichment, resulting in a higher overall groundwater vulnerability. Very high vulnerability and high vulnerability areas were mainly distributed in Zepu County, Shache County, Maigaiti County, Tumushuke City, and the eastern part of Bachu County. The pollution loading of groundwater was generally low, the main pollution sources were point source pollution caused by water-rock interaction, non-point source pollution caused by pesticides and fertilizers, and point source pollution caused by industry and life. The overall functional value of groundwater was low because of human economic activities, fine water quality, and good habitat quality. Groundwater pollution risk was generally low, and very high and high pollution risk areas accounted for 20.7% of the study area, mainly distributed in Shache County, Zepu County, Maigaiti County, Tumushuke City, and the western part of Bachu County. Natural conditions such as strong aquifer permeability, weak groundwater runoff conditions, large groundwater recharge modulus, low vegetation coverage, and strong water-rock interaction, coupled with frequent human activities such as application of agricultural fertilizers and discharge of industrial and domestic sewage, made the groundwater pollution risk higher in these areas. Groundwater pollution risk assessment provided strong data support for the optimization of the groundwater monitoring network and the prevention of groundwater pollution.

Hydrogeochemical and isotopic assessment for characterizing groundwater quality in the Mitidja plain (northern Algeria).

Coastal aquifer overexploitation represents a concerning trigger for water salinization around the world and especially in arid and semi-arid regions along with urban growth and urbanization, as well as land use human-induced changes. This study aims to assess the groundwater quality in the Mitidja alluvial aquifer (northern Algeria) along with its suitability for domestic and agricultural utilizations. A hydrogeochemical approach, based on the interpretation of groundwater physiochemical parameters (EC, pH, dry residue, Ca2+, Mg2+, Na+, K+, Cl-, SO42-, HCO3-, and NO3-) collected during the wet and dry periods for the years 2005 and 2017 along with an isotopic characterization, including stable isotopes to identify the recharge sources for the samples collected in October 2017, has been proposed. The results show the presence of three dominant hydrochemical facies: (i) calcium chloride, (ii) sodium chloride, and (iii) calcium bicarbonate. Groundwater mineralization and salinization are so ascribable carbonates and evaporitic dissolution, especially during the dry periods, and to the presence of seawater. Ion exchange significantly affects groundwater chemistry along with human activities which directly or indirectly contribute in raising groundwater salts concentration. Specifically, NO3- concentrations are very high in the eastern portion of the study area which is exposed to fertilizers pollution where also the Richards classification pointed out the necessity of limit water utilization for agricultural use. The δ2H = f(δ18O) diagram indicates that the recharge origin for this aquifer is mainly due to the oceanic meteoric rainwater from the Atlantic and the Mediterranean Sea. The methodology proposed in this study can be applied in the similar worldwide coastal areas in order to contribute and sustainable water resource management in these regions.

Geochemistry and assessment of groundwater resource in coastal arid region aquifer (Dahab delta, South Sinai, Egypt)

Dahab is a tourist city located in the Sinai Peninsula, downstream of the Dahab watershed, as a part of the arid coastal region. Groundwater samples have been collected from the Dahab delta and were tested for salinity, major ions, minor elements, and heavy metals to investigate the geochemical processes deteriorating the groundwater quality. The spatial distribution of major, minor, and trace elements integrated with the geochemical interrelationships using the cumulative salinity bases mixing curves have been utilized to investigate the main source(s) of groundwater recharge and salinization origin in Dahab delta aquifer. The groundwater salinity ranges from 339 upstream of Dahab watershed to 53,216 mg/L downstream in the delta area. The groundwater varies from fresh, brackish, and saline water. The spatial distributions of major ions, minor elements (Si, and Br), and heavy metals (B and Sr) confirm that the recharge comes from the upstream watershed. According to the mixing model curves, groundwater quality has declined due to interactions with the aquifer matrix, mixing with seawater, and rejected brine from the reverse osmosis desalination plants. The fresh/brackish groundwater classes have been recorded in the northwestern part of the study area close to the basement rocks, where the Quaternary aquifer receives considerable recharge through the underneath fractures, joints, and faults that enhance the subsurface recharge. The samples with a high saline groundwater class have been recorded in the eastern and southern parts of the delta, demonstrating the effects of seawater intrusion. Based on WHO guideline criteria, the assessment of groundwater for various uses has determined that most groundwater samples from the alluvial aquifer (91%) are unfit for human consumption. The Water Quality Index indicates that the groundwater in the southern part of the delta is not suitable for all uses due to mixing with the seawater, and injection of rejected brine water from the desalination plants. In the north, groundwater is unfit for drinking and aquatics, excellent for recreation, marginal for irrigation, and fair for livestock. The groundwater in coastal arid region aquifers has deteriorated due to seawater intrusion.