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Groundwater is a vital water supply available in Egypt. Hydrogeochemical processes are important in regulating groundwater quality, impacting human health. In this paper, the relationships between diverse groundwater quality parameters, potential sources of groundwater pollution, and overall health risk were assessed in the Assiut Province, Egypt. For this study, 108 groundwater samples were collected randomly from the study area and analyzed to evaluate their quality. The obtained data were compared to the limit values recommended by the World Health Organization and the Egyptian water standards. The combination of hydrogeochemical and statistical methods proved that the groundwater salinity ranged between fresh and slightly saline. Furthermore, the water–rock interactions, the return flow of the irrigation water, and agricultural fertilizers are the main factors controlling groundwater compositions. Based on human health consideration, 3.7%, 2.8%, 5.6%, 5.6%, and 17.6% of the groundwater samples are rated as poor water due to the elevated concentrations of EC, Ca2+, Mg2+, HCO3−, and SO42−, respectively. Ingesting this water presents a risk to human health and has a serious impact on the skin, hair, and eyes.

Groundwater sources are drastically changing in their quantity and quality depending on local and regional level natural and anthropogenic factors, influencing their suitability for drinking and irrigation purposes. The objective of this study is to characterize the hydrochemistry and assess the groundwater quality in the fluvial deltaic plains of Cauvery river basin, Tamil Nadu, India. A total of 50 georeferenced groundwater samples were collected across Needamangalam block of Thiruvarur district and analyzed for major ions and hydrochemical processes. The results showed an ionic sequence of Cl− > Na+ > HCO3− > Mg2+ > Ca2+ > CO32− > SO42− > K+ based on their relative proportions. The scatter diagram indicated that groundwater chemistry was mostly influenced by weathering dominance followed by evaporation and silicate weathering. The dominant hydro-chemical facies were Na+-Cl−-HCO3− type, Na+-Mg2+-Cl−-HCO3− type, Na+-Cl−-HCO3−-CO32− type and Na+-Mg2+-Cl−-HCO3−-CO32− type influenced by the ion-exchange reaction. Most of the groundwater samples are suitable for drinking and irrigation except few with higher Na+ and Cl− content caused by the mixing of salt from fluvio-marine sources or agriculture return flow. The high sodium content in irrigation water may affect the soil hydraulic and nutrient properties in the long run.

Increasing demand for water has put tremendous pressure on groundwater resources in the hard rock terrain, where groundwater is a major source of agriculture, domestic and industrial purposes. Here, in the present study, we have assessed groundwater abstraction and recharge using Groundwater Resources Estimation Committee-1997 (GEC-97) norms and Water Table Fluctuation approach for the Jhansi district in the Bundelkhand region, central India. The assessment of abstraction was about 50,943 hectare meters (ham), of which ~ 91% uses for agriculture and the remaining 9% for domestic and industrial practices. We have also assessed groundwater recharge based on all available sources such as canal, rainfall, irrigation return flow, surface water structures on an annual and seasonal scale. Our results suggest higher recharge of about 42% from irrigation return flow during non-monsoon season compared to monsoon season because of higher groundwater abstraction for irrigation purposes. The rainfall recharge was about 33% in the study area during the assessment year of 2016. In general, the assessed groundwater abstraction and recharge show marked spatial and seasonal variation across the study area. The assessment of groundwater resources during 2016 suggests a ‘safe’ category of groundwater development stage for Jhansi district. The high-spatial-resolution (block-wise) assessment suggests more than 60% groundwater development stage for two blocks in the Jhansi district required better groundwater management policy. The results obtained from the present study can be helpful for high-spatial-resolution groundwater resources management.

Accurate estimation of irrigation return flow plays an important role in the effective management of groundwater, especially in arid and semiarid irrigation regions. However, there is a lack of sufficient research to clarify hydrological process dynamics associated with irrigation return flow. In this study, first, a two-dimensional/three-dimensional model, HYDRUS-2D/3D, was adopted to analyze two different irrigation types in the Delingha Depression, which is located at the northeastern margin of the Qaidam Basin, China. Then, a 3D saturated flow model was established. This study determined the effect of agricultural water application on the dynamics of irrigation return flow. A large difference in the irrigation return-flow coefficient (IRFC) was seen during the growing season; an IRFC of 0.3 was obtained using flood irrigation, whereas ditch irrigation resulted in an IRFC of only 0.1. The lag time of recharge was approximately 150 days. It was necessary to consider the lag time for the 3D numerical model to obtain satisfactory results. Flood irrigation led to a groundwater recharge rate of 90 mm/year. These results indicate that the lag time should be considered when groundwater recharge is estimated or modeled.

Awareness concerning the degradation of groundwater quality and their exacerbating adverse effects due to salinization processes is gaining traction, raising for adequate understanding of the distribution, sources, genesis, and environmental concerns of salinity in groundwater. Saline groundwater is widely distributed all over the world, with an area of 24 million km2 (16% of the total land area on earth) and 1.1 billion people living in the affected areas, especially the arid/semi-arid areas in developing countries. These large-scale groundwater salinization problems are sourced from two major ways: natural and anthropogenic. The natural sources are diversified from connate saline groundwater, seawater intrusion, evaporation, dissolution of soluble salts, membrane filtration process to geothermal origin. The anthropogenic sources include irrigation return flow, road deicing salts, industrial and agricultural wastewater, and gas and oil production activities. The integrated approach of geochemical tracers and multiple isotopes (δ18OH2O, δ2HH2O, δ11B, δ36Cl, δ34Ssulfate, 87Sr/86Sr, and δ7Li) is proved to be useful in the constraints of the origin and transport of solutes in groundwater. Groundwater salinization is often associated with high levels of some toxic elements like arsenic, fluoride, selenium, and boron. Four "triggers" lead to this association: salt effect, competing adsorption, microbial processes, and cation exchange.

With the advancement of drilling technology along with assured availability of electricity ground water extraction for irrigation started increasing. The current study carried out at research farm of Raipur campus of Indira Gandhi Krishi Vishwavidyalaya, Raipur, Chhattisgarh facing the same problem. Study is performed with the aim to increase the utilisation of available surface water in the study area carried by diversion canal from one diversion structure (called Bharri dam) constructed on the rivulet in the study area (called Chhokranala). Actual carrying capacity of the diversion canal and other 6 drains in the study area was worked out on the basis of their existing dimensions and grades. Required discharge required to be carried out by the diversion canal and other six drains were also worked out on the basis of drainage coefficient. Based on the comparison of required discharge capacity with actual discharge capacity revised dimensions were proposed to drain out the study command quickly during the heavy rainfall. Total annual ground water recharge from the study area was assessed as 4,01,880 m³, which is sum of ground water recharges through infiltration, return flow due to surface irrigation by diversion canal, return flow due to bore well irrigation and recharge from tank/ponds (67,500 m³, 1,41,800 m³, 1,86,400 m³ and 6,180 m³ respectively).

The study area, between Borg El Arab and El Hammam, is recently subjected to intensive land reclamation projects aiming to cultivate about 57000 feddans. It is supplied by two main sources of irrigation, i.e. the surface water as a main source (Bahig canal and El Hammam canal), and the groundwater from more than 600 shallow wells tapping the Ralat aquifer (calcareous sandstone) of Plio-Pleistocene age as a supplement source. During the last three decades (1985 – 2014), conjunctive use of surface water together with groundwater has resulted in serious hydrologic problems e.g. water losses, canal seepage and water logging, where the depth to water level has risen up from about 20 m (1985) to less than 5.0 m (2014). Meanwhile, the groundwater salinity decreased during this period from more than 5000 ppm to less than 2000 ppm, indicating a dilution effect by seeped water. The water seepage from the dissecting canals is estimated in the present work by 65.18 x 106 m3/year replenishing the groundwater system in the down gradient areas. Might as well, the irrigation return flow through permeable soil in the study area is estimated by 4.125 x 106 m3/year due to the applied flood irrigation technique. In other words, 95% of the total groundwater replenishment is from the canal seepage, while only 5% from direct percolation. The investigation of wells tapping the Ralat aquifer in the study area has indicated that water levels are ranging from 21.0 m to 1.0 m above mean sea level. More than 57.6 x 106 m3/year (average 84% of the natural groundwater discharge) are pumping from such wells to get water of about 2000 ppm salinity, indicating a significant hydraulic connection between the surface water canals and the underlying aquifer. The calculated water balance of the Ralat aquifer has resulted in an amount of annual surplus water of the order of 11.705 x 106 m3/year as groundwater storage.

International audience; Large proportions of rain water and snowmelt infiltrate into the subsurface before contributing to stream flow and stream water quality. Subsurface flow dynamics steer the transport and transformation of contaminants, carbon, weathering products and other biogeochemistry. The distribution of groundwater ages with depth is a key feature of these flow dynamics. Predicting these ages are a strong test of hypotheses about subsurface structures and time varying processes. CFC‐based groundwater ages revealed an unexpected groundwater age stratification in a 0.47 km2 forested catchment called Svartberget in northern Sweden. An overall groundwater age stratification, representative for the Svartberget site, was derived by measuring CFCs from 9 different wells with depths of 2 m to 18 m close to the stream network. Immediately below the water table, CFC‐based groundwater ages of already 30 years that increased with depth were found. Using complementary groundwater flow models, we could reproduce the observed groundwater age stratification and show that the 30 year lag in rejuvenation comes from return flow of groundwater at a subsurface discharge zone that evolves along the interface between two soil types. By comparing the observed groundwater age stratification with a simple analytical approximation, we show that the observed lag in rejuvenation can be a powerful indicator of the extent and structure of the subsurface discharge zone, while the vertical gradient of the age‐depth relationship can still be used as a proxy of the overall aquifer recharge even when sampled in the discharge zone. The single age stratification profile measured in the discharge zone, close to the aquifer outlet, can reveal the main structure of the groundwater flow pattern from recharge to discharge. This groundwater flow pattern provides information on the participation of groundwater in the hydrological cycle and indicates the lower boundary of hydrological connectivity.

Evapotranspiration (ET) from riparian vegetation can be difficult to estimate due to relatively abundant water supply, spatial vegetation heterogeneity, and interactions with anthropogenic influences such as shallower groundwater tables, increased salinity, and nonpoint source pollution induced by irrigation. In semiarid south‐eastern Colorado, reliable ET estimates are scarce for the riparian corridor that borders the Arkansas River. This work investigates relationships between the riparian ecosystem along the Arkansas River and an underlying alluvial aquifer using ET estimates from remotely sensed data and modelled water table depths. Results from a calibrated, finite‐difference groundwater model are used to estimate weekly water table fluctuations in the riparian ecosystem from 1999 to 2009, and estimates of ET are calculated using the Operational Simplified Surface Energy Balance (SSEBop) model with over 200 Landsat scenes covering over 30 km² of riparian ecosystem along a 70‐km stretch of the river. Comparison of calculated monthly SSEBop ET to estimated alfalfa reference ET from local micrometeorological station data indicated statistically significant high linear correspondence (R² = .87). Daily calculated SSEBop ET showed statistically significant moderate linear correspondence with data from a local weighing lysimeter (R² = .59). Simulated monthly SSEBop ET values were larger in drier years compared with wetter years, and ET variability was also larger in drier years. Peak ET most commonly occurred during the month of June for all 11 years of analysis. Relationships between ET and water table depth showed that peak monthly ET was highest when groundwater depths were less than about 3 m, and ET values were significantly lower for groundwater depths greater than 3 m. Negative sample Spearman correlation highlighted riparian corridor locations where ET increased as a result of decreased groundwater depths across years with different hydroclimatic conditions. This study shows how a combination of remotely sensed riparian ET estimates and a regional groundwater model can improve our understanding of linkages between riparian consumptive use and near‐river groundwater conditions influenced by irrigation return flow and different climatic drivers.

Identifying the key factors controlling groundwater chemical evolution in mountain‐plain transitional areas is crucial for the security of groundwater resources in both headwater basins and downstream plains. In this study, multivariate statistical techniques and geochemical modelling were used to analyse the groundwater chemical data from a typical headwater basin of the North China Plain. Groundwater samples were divided into three groups, which evolved from Group A with low mineralized Ca‐HCO₃ water, through Group B with moderate mineralized Ca‐SO₄‐HCO₃ water, to Group C with highly saline Ca‐SO₄ and Ca‐Cl water. Water‐rock interaction and nitrate contamination were mainly responsible for the variation in groundwater chemistry. Groundwater chemical compositions in Group A were mainly influenced by dissolution of carbonates and cation exchange, and suffered less nitrate contamination, closely relating to their locations in woodland and grassland with less pronounced human interference. Chemical evolution of groundwater in Groups B and C was gradually predominated by the dissolution of evaporites, reverse ion exchange, and anthropogenic factors. Additionally, the results of the inverse geochemical model showed that dedolomitization caused by gypsum dissolution, played a key role in the geochemical evolution from Group A to Group B. Heavy nitrate enrichment in most groundwater samples of Groups B and C was closely associated with the land‐use patterns of farmland and residential areas. Apart from the high loads of chemical fertilizers in irrigation return flow as the main source for nitrate contamination, the stagnant zones, flood irrigation pattern, mine drainage, and groundwater‐exploitation reduction program were also important contributors for such high mineralization and heavy NO₃⁻ contents in Group C. The important findings of this work not only provide the conceptual framework for the headwater basin but also have important implications for sustainable management of groundwater resources in other headwater basins of the North China Plain.

Hydrochemical studies carried out on the groundwater in north eastern part of Jordan valley, Jordan, revealed the confinement of groundwater to two partly overlapping Upper Cretaceous and Tertiary-Quaternary aquifers. Values of Base Exchange Index (r1) and Meteoric Genesis Index (r2) indicate that the groundwater is essentially Na-SO4 type and belongs mainly to the category of Deep Meteoric Percolation type. Major processes responsible for the hydrochemistry of groundwater are: weathering of carbonate and silicate minerals aided by H2CO3 and H2SO4, oxidation of sulphide minerals, domestic waste water, irrigation return flow, reverse and direct ion exchange reactions as well as connate saline water. Values of Water Quality Index indicate the occurrence of excellent and good quality potable water at majority of bore well locations. The groundwater belongs essentially to (C3S1) and (C4S2) irrigation water classes of Richards (1954) and is suitable for cultivation of semi-salt tolerant and salt tolerant crops. Keywords: Hydrogeochemistry, Sources of dissolved solids, Water Quality Index, Jordan valley region, Jordan

A thorough study on understanding of groundwater recharge sources and mechanisms was attempted by integrating the hydrogeological, geochemical and isotopic information along with groundwater dating and end-member mixing analysis (EMMA). This study was necessitated due to prolonged dryness and unavailability of freshwater in semi arid Deccan trap regions of Central India. In addition, groundwater resources are not characterized well in terms of their geochemical nature and recharge sources. The hydrogeochemical inferences suggest that aquifer I consists of recently recharged water dominated by Ca–Mg–HCO3 facies, while groundwater in aquifer II shows water–rock interaction and ion exchange processes. Presence of agricultural contaminant, nitrate, in both aquifers infers limited hydraulic interconnection, which is supported by unconfined to semi-confined nature of aquifers. Groundwater in both aquifers is unsaturated with respect to carbonate and sulfate minerals indicating lesser water–rock interaction and shorter residence time. This inference is corroborated by tritium age of groundwater (aquifer I: 0.7–2 years old and aquifer II: 2–4.2 years old). Stable water isotopes (δ2H, δ18O) suggest that groundwater is a mixture of rainwater and evaporated water (surface water and irrigation return flow). EMMA analysis indicates three groundwater recharge sources with irrigation return flow being the dominant source compared to others (rainwater and surface waters). A conceptual model depicting groundwater chemistry, recharge and dynamics is prepared based on the inferences.

Estimation of groundwater recharge is more essential for managing aquifers, particularly in arid regions with limited access to water resources. Low potentiality of aquifer recharge, deep groundwater levels and impacts from other important sources like irrigation return flow add more complexities to estimating recharge in these areas. In this research, physical and chemical (tracer) techniques including water-table fluctuation (WTF), chloride mass balance (CMB), stable isotopes (2H and 18O) and water-budget equation (WBE) were applied to estimate recharge into the Birjand alluvial aquifer in arid areas of SE Iran with a mean annual precipitation of about 147 mm. Recharge rates, in ascending order, were calculated about 5.0, 9.2, 33.2 and 41.7 mm year−1 using isotopes, CMB, WTF and WBE methods, respectively. Isotopes and chloride tracers assessed the rainfall-related aquifer recharge, while the other methods represented total recharge including rainfall infiltration plus deep percolation of irrigation water (irrigation return flow). Total recharge rate of the Birjand aquifer was estimated in average at 37.5 mm year−1, partitioned between the rainfall recharge (7.0 mm year−1) and irrigation return flow (30.5 mm year−1). The values represent an average rainfall recharge coefficient of about 4.8% of the annual precipitation and return flow coefficient of 15% of the total annual applied water for irrigation. Recharge estimates are recommended as initial guesses for calculating water-balance in order to manage valuable groundwater resources in other arid-land aquifers. The study highlighted priorities of the stable isotope and WTF methods in estimating rainfall and total (rainfall + return flows) recharge of the groundwater in arid regions, respectively.

Issues of declining water levels and groundwater contamination are reported in parts of Rajasthan in recent times. One of the major contaminants present in the groundwater was found to be uranium. This study was carried out to determine the level of uranium contamination in Jaipur and Dausa districts of Rajasthan state and to evaluate its correlation with physicochemical parameters and stable isotopes (δ2H and δ18O). Results indicate that the dissolved uranium concentration ranges from 5 to 145 µg/l with an average concentration of 49 µg/l. Correlations of dissolved uranium with depth, physico-chemical parameters and stable isotopes were used for deducing the source of U in groundwater and release mechanism. Stable isotope data indicate three major sources of groundwater recharge; (i) evaporative surface water or contribution from irrigational return flow, (ii) evaporated rainwater and (iii) direct precipitation without evaporation. Vertical correlation of EC in groundwater indicates flushing of the local groundwater by regional groundwater flows. No correlation was observed between dissolved U and the corresponding δ18O composition. Hydrochemical and isotopic results infer that leaching of minerals present in the subsurface is the main cause for elevated levels of U in the study area.

Coarse temporal (i.e., annual) and spatial (i.e., watershed) scales camouflage water stress associated with withdrawals from surface water and groundwater sources. To address this "curse of scale", we developed a framework to characterize water stress at different time scales and at fine spatial scales that have not been explored before. Our framework incorporates surface water-groundwater interactions by accounting for spatially cumulative consumptive and nonconsumptive use impacts and associated changes in flow due to depletion and return flow along stream networks. We apply the framework using a rich data set of water withdrawals from more than 6800 principal facilities (i.e., withdrawal capacity >380 000 L/day) across the U.S. Great Lakes Basin. Results underscore the importance of spatiotemporal scale and return flows when characterizing water stress. Although the majority of catchments in this water-rich region do not experience large stress, a number of small headwater catchments with sensitive streams are vulnerable to flow depletion caused by surface water and shallow groundwater withdrawals, especially in a high-withdrawal, low-flow month (e.g., August). The return flow from deep groundwater withdrawals compensates for the streamflow depletion to the extent that excess flow is likely in many catchments. The improved ability to pinpoint the imbalance between natural water supply and withdrawals based on stream-specific ecological water stress thresholds facilitates protecting fragile aquatic ecosystems in vulnerable catchments.

Documenting the sources and residence times of water that contributes to streamflow is important for understanding processes in river catchments. The residence times of bank storage and return flow and its influence on river water chemistry in the upper Barwon River of southeast Australia were investigated using stable (18O, 2H, and 13C) and radioactive (3H and 36Cl) isotopes, major ion geochemistry, river discharge data, and electrical conductivity (EC)-discharge hysteresis. Elevated 3H activities following high winter flows indicate that bank storage and return flow contributes to river discharge for at least several months. However, EC-discharge hysteresis patterns suggest that individual storm events make additional contributions to bank storage and return flow throughout the year over periods of a few weeks. 3H activities in the upper Barwon River are >1.75 TU throughout the year, suggesting that the contribution of older regional groundwater, which has 3H activities

Impact of irrigation return flow induced mineral weathering and ion exchange reactions in the groundwater was studied in Limpopo region, South Africa . Based on EC (>500) and HCO 3 (>150 mg/l), groundwater samples are classified into two groups due to its heterogeneous nature. Water types in group 1 and 2 wells are Ca-Mg-Cl-SO4 and Ca-Mg-HCO3, respectively. Gibbs plots, bivariate plots and ionic ratios (Mg/Na vs Ca/Na; HCO3/Na vs Ca/Na; mCa + Mg vs mHCO3; mNa + K vs mHCO3; Ca + Mg-HCO3-SO4 vs Na + K-Cl; mCa + Mg/HCO3 vs Cl; Ca + Mg/SO4 +HCO3 >1; Na/Cl ratio; Cl + SO4 vs HCO3 ), chloro alkaline indices (CAI, CA2) and Pearson correlation analysis imply that groundwater chemistry is influenced by mineral weathering (carbonate > silicate minerals), reverse ion exchange and irrigation return flow. In group 1 wells, Cl + SO 4 and HCO3 have strong positive correlation and both increases together, suggesting induced mineral weathering caused by nitrification and wastewater infiltration from the surface. Group 2 wells are generally deep with low groundwater level fluctuation and high concentration of major ions. Overall, water chemistry in the group 1 wells is highly affected by the contamination sources than group 2 wells.

Coastal aquifers are highly vulnerable to salinization, especially by seawater intrusion. This problem is exacerbated by increasing demands for freshwater in coastal zones due to urbanization and industrialization. This paper investigates seawater intrusion in coastal aquifers of Kachchh district in Gujarat, an economic hub of the country in western India. A total of 26 groundwater samples were collected from various villages of the district from Kandla to Mandavi. In this study hydro-chemical, stable isotope (δ18O and δD) and GIS analysis were used to infer salinization processes. The origin of salinity and mixing of various water masses has been studied through the integration of major ions chemistry with stable isotopes δ18O and δD. Most of the samples were showing Na-Cl type water facies. It was observed that besides natural processes (such as water–rock interaction, ion exchange, dissolution/precipitation dynamics and evaporation) which are governing the groundwater quality, current land use practices have augmented the salinization in this poorly drained semi-arid area. Various ionic ratios (such as Mg2+/Ca2+, Na+/Cl−, SO42−/Cl−, K+/Cl−) and isotopic composition (δ18O and δD) of groundwater suggest that while in coastal areas seawater intrusion and formation of saline plumes is taking place, due to upconing of underlying natural saline water which is enhanced by overexploitation. In inland areas groundwater quality is deteriorating due to infiltration of wastewater and irrigation return flow. The continued stress on land and water resources has shifted the natural balance and accelerated the salinization process in this water scarce region. For securing freshwater in future, the integrated water resources management is required which should also include calculation of groundwater budget in the coastal aquifer.

Documenting the distribution, sources and fluxes of baseflow discharge into rivers is important for their management and for maintaining ecosystem health. This study uses major ion geochemistry, 222Rn, and 3H to differentiate between the input of low-salinity near-river waters (bank storage and return waters and/or interflow) and regional groundwater in an intermittent river from southeast Australia that is undergoing long-term changes in flow resulting from climate change. Baseflow discharge calculated by 222Rn mass balance was up to 1.3 m3/m/day in the high flow period in July 2019 and up to 0.1 m3/m/day at low flow conditions in November 2019. The distribution of 222Rn activities implies higher baseflow fluxes in the upper and middle reaches that have relatively steep topography and higher hydraulic gradients. The lower reaches received less baseflow due to subdued topography and fine-grained sediments. The observation that Cl concentrations did not increase uniformly downstream, however, implies that much of the baseflow may comprise bank return flow or interflow. This conclusion is also consistent with water mass balance calculations and the observation that 3H activities (1.85-3.00 TU) in the river were higher than in the groundwater (

Climate models for the 21st century project further reduction in the warm season precipitation and more frequent droughts across Mexico. In the possible scenario of enhanced aridity from global warming, the δ18O (−10.6 to −6.3 ‰) and δ2H (−71.1 to −57.1 ‰) compositions and deuterium-excess (0.2–14.6‰) of shallow groundwater from two different basins (Sandia and El Potosi) with similar geological and geomorphological settings were considered to evaluate the influences of early summer rainfall and later summer tropical storms on aquifers at water-scarce southeast margin of the Chihuahuan Desert. Groundwater of the Sandia Basin was recharged mainly from tropical storms. Higher CO2 partial pressure (log pCO2: −2.70 to −1.61) caused more gypsum dissolution (Ca–Mg–SO4 facies) and the effect of irrigation return flow (Ca–Mg–Cl facies) was minor. Even though the El Potosi Basin is in proximity, its groundwater was recharged from both the early and late summer precipitations. The multivariate factor analysis helped to separate the process of rock-water interactions from the recharge seasonality. Gypsum dissolution was less as the partial pressure of CO2 was comparatively lower (log pCO2: −3.01 to −2.15), and the ion exchange along with carbonate mineral dissolutions led to Ca–Mg–HCO3 facies. Over-exploitation under the condition of reduced warm season rainfall would continue to enhance the salinity of groundwater in this region. Hence, the drought mitigation policies should prioritize sustainability of the depleted aquifers and cultivation of salinity resistant crops.

Yinchuan Plain is a typically intensive cultivated region in the northwest of China. The irrigation return infiltration from Yellow River is the main source of groundwater recharge. Deep soil layers, sandy vadose zones, and dense irrigation canals make the groundwater susceptible to the return flow which contains pollutants originating mainly from agriculture applications, particularly from the extensive use of nitrogen fertilizer and manure. The pollution levels of phreatic water and confined water in NWS areas (non-water source areas) and WS areas (water source areas) of Yinchuan Plain in 2004 and 2014 were evaluated by the single-factor evaluation method, fuzzy comprehensive evaluation method, and average benchmark coefficient method, respectively. Piper trilinear diagram and scatter plots of major ions were used to classify water types and chemical facies, and further analyze the causes of groundwater pollution and the variation tendency of agricultural pollution. The results show that in 2014, about 50% of the groundwater samples were heavily polluted in Yinchuan Plain, the pollution level of phreatic water and confined water in NWS areas was up to level 5. And the groundwater within the standard in 2004 was heavily polluted in 2014 in WS areas, three-nitrogen pollution was the most serious pollutant, and the organic pollution level was grade IV. From the scatter plots of ions, it can be seen that the increase in concentrations of major ions was affected by evaporation-condensation and cation exchange reaction, but the complex ion contents indicated that groundwater was affected by human activities. The intensive agricultural activities, such as over fertilization, artificial irrigation, have led to concentrations increase of some chemical composition in groundwater.

Study region: Northeastern Iran. Study focus: In northeastern Iran, water needed for municipal and agricultural activities mainly comes from groundwater resources. However, it is subject to substantial anthropogenic and geogenic contamination. We characterize the sources of groundwater contamination by employing an integrated approach that can be applied to the identification of large-scale contamination sources in other regions. An existing dataset of georeferenced water quality parameters from 676 locations in northeast of Iran was analyzed to investigate the geochemical properties of groundwater. Gridding of the parameters graphically illustrates the areas affected by high concentrations of As, Cl−, Cr, Fe, Mg2+, Na+, NO3−, Se, and SO42-. We then identified potential anthropogenic and geogenic contamination sources by employing random forest (RF) regression modeling. New hydrological insights for the region: Random forest (RF) models show that the major ions, As, Cr, Fe, and Se content of groundwater are mainly determined by geology in the study area. Modeling also links groundwater NO3− contamination with sewage discharge into aquifers as well as the application of nitrogenous and animal-waste fertilizers. Areas of high salinity result from evaporate deposits and irrigation return flow. Medium to high non-carcinogenic health risk is found in areas with high concentrations of geogenic As and Cr in groundwater. Our approach can be applied elsewhere to analyze regional groundwater quality and associated health risks as well as identify potential sources of contamination.

GangaWIS is a comprehensive tool that integrates various hydrological components of the Ganga River basin and supports the policymakers in analyzing the impact of future developments and climate change scenarios in combination with multiple interventions. It describes the functioning of the water system of the Ganga basin within India concerning rainfall-runoff, surface water and groundwater flow, storage and diversion of water for various purposes, water quality, and ecology. The hydrology and the rainfall-runoff process has been divided into two different models: SPHY and WFlow. They are both fully distributed models working on a grid of square cells. SPHY is used to describe the hydrological process in the mountainous areas in the Himalaya. The rainfall-runoff processes for the non-mountainous part of the Ganga Basin are simulated with the WFlow model. The river discharges calculated by the SPHY model for the Himalayas are used as upstream boundaries for the WFlow model. The water resources model RIBASIM describes the management and use of water. Its hydrological input is derived from the river discharges calculated by WFlow. RIBASIM uses a schematization of links and nodes to describe the flow of water in the rivers, the storage in reservoirs, the diversion into canals, and the use and return flow by different functions. Furthermore, return flows can be divided over rivers, canals, and Groundwater. The information on discharges and water levels calculated by RIBASIM are used by the groundwater model to describe the interaction between surface and Groundwater. Groundwater movement is simulated with iMOD, the Deltares extension of the well-known MODFLOW code for solving the groundwater flow equation. iMOD uses the same calculation grid as Wflow but is only applied to the alluvial fraction of the basin. The Ganga river basin model is capable of assessing the impacts of future developments/climate change scenarios and various interventions/measures at basin scale by comparison of simulation results. Using this model, different scenarios are developed: present, pristine, and 2040 with three different possible climate change developments: no climate change, climate change following the RCP4.5 scenario, and climate change following the RCP8.5 scenario. The scenarios used model parameters such as precipitation, temperature, land use, infrastructure, population, industry, and agriculture to develop a corresponding model output of the river flow, water quality, and groundwater levels. The dashboard of GangaWIS depicts the various indicators to assess the impact of the different scenarios, such as state of groundwater development, lowest discharge, volume of water stored in reservoirs, agricultural crop production, deficit irrigation, and drinking water, surface water quality index, the amount of Groundwater extracted and ecological, hydrological and socio-economic status. GangaWIS can be used to analyze and visualize various data (temporal/spatial) and model results, and it can provide relevant measured and modeled information to multiple users such as data managers, modelers, policymakers, and decisionmakers.

Groundwater is being continuously stressed and contaminated due to human activities. The increased use of fertilizers, pesticides and other chemicals in the agriculture is leading to the deterioration in quality due to return flow. Groundwater quality analysis therefore becomes pre-requisite for the planning and analysis purpose for ensuring domestic supplies in an area. The present study deals with spatio-temporal analysis and monitoring of groundwater quality for domestic purpose in district Hisar of Haryana, India. Groundwater quality data of total of 87 observation wells of the study area for years 2000 and 2014 was used for this purpose. The analysis of various parameters of water quality such as Electrical Conductivity (EC), Hydrogen Ion Concentration (pH), Residual Sodium Carbonate (RSC), Sodium Adsorption Ratio (SAR) and Total Dissolved Solids (TDS) was carried out. To estimate the acceptable quality of water for domestic use, the area was divided into various categories of suitability as per various international and national standards. Spatial distribution maps of EC, pH, RSC, SAR and TDS were generated and integrated using GIS for demarcating different suitability zones of groundwater quality for domestic use. Integrated groundwater quality maps were prepared for the years 2000 and 2014. The study indicated that the maximum area of Hisar district was found in good to permissible category for year 2000 whereas in permissible to doubtful category for the year 2014 for drinking purpose. The present paper describes in detail the spatio-temporal characteristics of various suitability categories of groundwater for domestic use.

Comprehensive national estimates of groundwater storage loss (GSL) are needed for better management of natural resources. This is especially important for data scarce regions with high pressure on groundwater resources. In Iran, almost all major groundwater aquifers are in a critical state. For this purpose, we introduce a novel approach using Artificial Intelligence (AI) and machine learning (ML). The methodology involves water budget variables that are easily accessible such as aquifer area, storage coefficient, groundwater use, return flow, discharge, and recharge. The GSL was calculated for 178 major aquifers of Iran using different combinations of input data. Out of 11 investigated variables, agricultural water consumption, aquifer area, river infiltration, and artificial drainage were highly associated to GSL with a correlation of 0.84, 0.79, 0.70, and 0.69, respectively. For the final model, 9 out of the totally 11 investigated variables were chosen for prediction of GSL. Results showed that ML methods are efficient in discriminating between different input variables for reliable GSL estimation. The Harris Hawks Optimization Adaptive Neuro-Fuzzy Inference System (HHO-ANFIS) and the Least-Squares Support Vector Machine (LS-SVM) gave best results. Overall, however, the HHO-ANFIS was most efficient to predict GSL. AI and ML methods can thus, save time and costs for these complex calculations and point at the most efficient data inputs. The suggested methodology is especially suited for data-scarce regions with a great deal of uncertainty and a lack of reliable observations of groundwater levels and pumping.

The main groundwater aquifer in El Fayoum region is a Quaternary aquifer. It shows increasing signs of groundwater quality deterioration. Therefore, a comprehensive assessment of groundwater quality has been performed for determining the geochemical processes affecting the groundwater quality evolution and assessing groundwater quality for drinking and irrigation uses. Physicochemical parameters, geochemical model (NETPATH), and water quality indices (WQIs) are applied to improve water quality assessment and controlling mechanisms with help of statistical analysis and GIS techniques. Thirty-eight groundwater samples from the Quaternary aquifer at depths less than 60 m and 12 irrigation drainage samples were collected. Thirteen physicochemical parameters including temperature (°C), TDS, pH, EC, K+, Na+, Ca+2, Mg2+, HCO3−, Cl−, SO42−, CO32−, and NO3− were measured by standard analytical techniques. The analytical findings reveal that the groundwater facies are Na-Cl, mixed Ca-Mg-Cl, and Na-Ca-HCO3 water types. In addition, the minerals saturation indices (SI) estimated by a geochemical model revealed that the groundwater samples are supersaturated by kaolinite, Ca-montmorillonite, dolomite, gibbsite, calcite, quartz, and aragonite and are unsaturated by gypsum, anhydrite, and partial pressure of CO2. The drinking water quality index (DWQI) results revealed that 58% of the groundwater samples are very poor quality, while 42% of samples are unsuitable for drinking uses. The irrigation water quality index (IWQI) results revealed that all groundwater samples range from 26.1 to 36.1, indicating a medium class of quality for irrigation purposes. These results reflect the influences of the high mineralization processes, cumulative effect of cation exchange, leaching processes from aquifer materials, contamination by irrigation return flow, and seepage from drains on the groundwater quality. In conclusion, utilization of physicochemical parameters, geochemical model, and WQIs can be considered as a promising and applicable approach to determine the controlling geochemical mechanisms and for assessing of groundwater quality in El Fayoum Depression, Egypt.

During the last decades, the endorheic Lake Urmia basin in northwestern Iran has suffered from declining groundwater tables and a very strong recent reduction in the volume of Lake Urmia. For the case of Lake Urmia basin, this study explores the value of different locally and globally available observation data for adjusting a global hydrological model such that it can be used for distinguishing the impacts of human water use and climate variations. The WaterGAP Global Hydrology Model (WGHM) was for the first time calibrated against multiple in situ and spaceborne data to analyze the decreasing lake water volume, lake river inflow, loss of groundwater, and total water storage in the entire basin during 2003–2013. The calibration process was done using an automated approach including a genetic algorithm (GA) and non-dominated sorting genetic algorithm II (NSGA-II). Then the best-performing calibrated models were run with and without considering water use to quantify the impact of human water use. Observations encompass remote-sensing-based time series of annual irrigated areas in the basin from MODIS, monthly total water storage anomaly (TWSA) from GRACE satellites, and monthly lake volume anomalies. In situ observations include time series of annual inflow into the lake and basin averages of groundwater level variations based on 284 wells. In addition, local estimates of sectoral water withdrawals in 2009 and return flow fractions were utilized. Calibration against MODIS and GRACE data alone improved simulated inflow into Lake Urmia but inflow and lake volume loss were still overestimated, while groundwater loss was underestimated and seasonality of groundwater storage was shifted as compared to observations. Lake and groundwater dynamics could only be simulated well if calibration against groundwater levels led to an adjustment of the fractions of human water use from groundwater and surface water. Thus, in some basins, globally available satellite-derived observations may not suffice for improving the simulation of human water use. According to WGHM simulations with 18 optimal parameter sets, human water use was the reason for 52 %–57 % of the total basin water loss of about 10 km3 during 2003–2013, for 39 %–43 % of the Lake Urmia water loss of about 8 km3, and for up to 87 %–90 % of the groundwater loss. Lake inflow was 39 %–45 % less than it would have been without human water use. The study shows that even without human water use Lake Urmia would not have recovered from the significant loss of lake water volume caused by the drought year 2008. These findings can support water management in the basin and more specifically Lake Urmia restoration plans.

Nitrate concentrations in groundwater have been historically high (N≥11.3 mg L−1) in an area surrounding Tinwald, Ashburton, since at least the mid-1980s. The local community is interested in methods to remediate the high nitrate in groundwater. To do this, they need to know where the nitrate is coming from. Tinwald groundwater exhibits two features stemming from irrigation with local groundwater (i.e. irrigation return flow). The first feature is increased concentrations of nitrate (and other chemicals and stable isotopes) in a “hotspot” around Tinwald. The chemical concentrations of the groundwater are increased by recirculation of water already relatively high in chemicals. The irrigation return flow coefficient C (irrigation return flow divided by irrigation flow) is found to be consistent with the chemical enrichments. The stable isotopes of the groundwater show a similar pattern of enrichment by irrigation return flow of up to 40 % and are also enriched by evaporation (causing a loss of about 5 % of the original water mass). Management implications are that irrigation return flow needs to be taken into account in modelling of nitrate transport through soil–groundwater systems and in avoiding overuse of nitrate fertiliser leading to greater leaching of nitrate to the groundwater and unnecessary economic cost. The second feature is the presence of “denitrification imprints” (shown by enrichment of the δ15N and δ18ONO3 values of nitrate) in even relatively oxic groundwaters. The denitrification imprints can be clearly seen because (apart from denitrification) the nitrate has a blended isotopic composition due to irrigation return flow and N being retained in the soil–plant system as organic N. The nitrate concentration and isotopic compositions of nitrate are found to be correlated with the dissolved oxygen (DO) concentration. This denitrification imprint is attributed to localised denitrification in fine pores or small-scale physical heterogeneity where conditions are reducing. The implication is that denitrification could be occurring where it is not expected because groundwater DO concentrations are not low.

Environmental tracers were used to characterize the origin and determine the age of the groundwater in the Motril-Salobrena aquifer (south-eastern Spain). The stable isotope concentrations (delta O-18/delta H-2), compared to the results obtained in previous studies, indicate that most of the recharge during the sampling period was from irrigation return flow and the carbonate Escalate aquifer. The combined dating of H-3, He-3, He-4, Kr-85, and Ar-39 allowed establishing the presence of modern water throughout the aquifer, although with different mixing percentages. Thus, there is a large zone characterized by a fluvial domain with 100% young waters ( 170 years), and the percentage of young water is reduced (22.5%). This is explained by the greater distance that groundwater travels (aquifer thicknesses is over 250 m) and the lower permeability of the aquifer in the deeper sectors.

The North China Plain is the main grain production district in China, with a large area of well irrigation resulting in a large groundwater depression cone. In the 1970s and 1980s, small-scale managed aquifer recharge (MAR) projects were developed to recharge shallow groundwater, which played an important role in ensuring stable and high crop yields. MAR projects are divided into 10 types based on local water conservancy characteristics. The combined use of well&ndash, canal irrigation has been widespread in the Yellow River Irrigation District of Shandong Province for nearly 40 years, where canals play multiple roles of transporting and storing Yellow River water or local surface water, recharging groundwater and providing canal irrigation. Moreover, the newly developed open channel&ndash, underground perforated pipe&ndash, shaft&ndash, water saving irrigation system can further expand the scope and amount of groundwater recharge and prevent system clogging through three measures. Finally, an adaptability zoning evaluation system of water spreading has been established in Liaocheng City of Shandong Province based on the following five factors: groundwater depth, thickness of fine sand, specific yield, irrigation return flow, and groundwater extraction intensity. The results show that MAR is more adaptable to the western region than to the eastern and central regions.

A calibrated fate and reactive transport model is applied to evaluate alternative water and land best management practices (BMPs) in Colorado’s intensively irrigated Arkansas River Valley to attenuate nonpoint source pollution and more closely meet regulatory standards for selenium (Se) and nitrogen (N) in groundwater and streams. Reduced irrigation (RI), lease fallowing (LF), canal sealing to reduce seepage (CS), reduced fertilizer application (RF), and enhanced riparian buffers (ERB) are explored as stand-alone BMPs, and in combination, at basic to more aggressive levels of implementation. The distributed-parameter model, which couples MODFLOW-SFR with RT3D-OTIS, predicts impacts that vary significantly over a region encompassing about 500 km2 and across time. Results suggest that, over the course of several decades, average Se and nitrate-nitrogen (NO3-N) groundwater concentrations within the region could be lowered by as much as 23% and 40%, respectively, using combined BMPs. Average Se concentration in the river could be decreased by up to 56% with combined BMPs, and NO3-N concentrations by up to 32% by using ERB. The CS-RF-ERB combination type may be the most promising for simultaneously lowering both Se and NO3-N concentrations. To insure compliance with Colorado water rights and the Arkansas River Compact with Kansas, measures must be taken to compensate for altered return flow patterns that will be a consequence of BMP implementation. Results also point to the need to consider the targeting of BMPs to specific locations within the region to maximize their effectiveness and efficiency.

Hydrochemical investigations, including geochemical analyses, multivariate statistics and geostatistics, were conducted to assess the factors that influence groundwater geochemistry and pollution potentiality in Luxor area, Upper Egypt. A total of thirty-one groundwater and surface water samples from the Quaternary aquifer and the River Nile were analyzed for fourteen physical and chemical variables for each sample. Spatial variations in total dissolved solids and nitrate concentration were mapped. Piper and Durov diagrams indicate that the hydrochemistry of groundwater is influenced by the secondary processes; mixing with fresh water from the River Nile and El Kalabia Canal, irrigation return flow, and sewage leakage, and reverse ion-exchange process. The hydrochemical modeling of mineral phase saturation indices shows that nearly all of the groundwater points are undersaturated with reference to calcite, aragonite, dolomite, anhydrite, gypsum, and halite. Correlation coefficients of the different variables are consistent with the saturation indices. Cluster analysis was used to identify four significant, distinct groundwater zones where the original groundwater was influenced differently by mixing processes. Factor analysis showed four mutually interfering factors reveal the chemical characteristics of the groundwater; these factors are caused by rock-water interactions, mixing of waters of different origins, and anthropogenic effects. Integration of hydrochemical and statistical analyses approach can be applied for the better management of water resources at a regional scale and in areas with comparable conditions.

High level of arsenic-containing groundwater has been used for irrigation purposes for several decades in Asia, leading to fluctuating water table and redox conditions in the unsaturated zone, thereby potentially affecting the mobilization of arsenic in the unsaturated and saturated zones. A field plot experiment was conducted in the arsenic – affected area of the Datong Basin, China to determine the effects of irrigation return flow on the hydrogeochemical behavior of arsenic and iron in the unsaturated zone. High-arsenic groundwater was extracted from a shallow aquifer far from the irrigation site and used as irrigation water. Soil water/shallow groundwater and soil/sediment samples were collected at different depths from the field site during the experiment. Water samples were analyzed to determine hydrochemical properties and arsenic concentrations, and soil/sediment samples were analyzed to determine total iron and arsenic. Infiltration of irrigation water into the unsaturated zone led to fluctuations in the water table, varying redox conditions, and the redistribution of arsenic and iron in the near-surface soil/sediment. Soil/sediment bulk geochemical analysis results indicate obvious increases of arsenic and iron in topsoil after irrigation. Infiltration of irrigation water carrying organic matter, sulfate, and nitrate into the subsurface affects the (bio)geochemistry of the unsaturated and saturated zones, and ultimately the behavior of arsenic and iron. Geochemical modeling results suggest desorption and leaching processes are responsible for the temporal changes of arsenic concentrations in both pore water, groundwater and sediment during irrigation. The results of this study indicate that flood irrigation using arsenic-contaminated groundwater should be controlled and gradually replaced by drip irrigation, sprinkler irrigation or irrigation using non-contaminated water resources to mitigate arsenic accumulation in the unsaturated zone and shallow groundwater.

During the last 25 years, rapid and unplanned land reclamation activity has been carried out in the areas located in both south and east of Wadi El - Natrun Depression of Egypt. Accordingly, negative effects on groundwater levels and vulnerability are frequently caused by localized high levels of abstraction and the return-flow of polluted irrigation water respectively. A groundwater model is a computational method that presents an approximation of an underground water system. In this study the groundwater system is simulated both in quantity and quality by using Mass Balance Transfer Model (NETPATH), Groundwater Modeling System (GMS) and DRASTIC Model to investigate the water - rock interactions, groundwater levels drawdown and vulnerability respectively. Three main geochemical processes namely dedolomitisation, dissolution of halite and silicate weathering were estimated during the flow path. The present over-abstraction of groundwater (105.84 million m3/year) has induced a general head drawdown from 3 to 40 m in years 2015 and 2050 respectively. Best estimate using a 3D GMS hydraulic model was (157000 m3/day) a strategy proposed for the management of groundwater without critical depletion (second scenario). The results document the extent to which a high drawdown can greatly reach 4 m by the end of simulation year 2050. The vulnerability maps of groundwater were constructed using the DRASTIC index method. The results indicated that, the southeastern and central portions of the study area are having high vulnerability rate (> 110). Modified DRASTIC map showed many more dominant high risk areas in the eastern parts of the study area that were low risk, which may be attributed to return flow of polluted irrigation water.

Mountainous areas are characterized by steep slopes and rocky landforms, with hydrological conditions varying rapidly from upstream to downstream, creating variable interactions between groundwater and surface water. In this study, mechanisms of groundwatersurface water interactions within a headwater catchment of the North China Plain were assessed along the stream length and during different seasons, using hydrochemical and stable isotope data, and groundwater residence times estimated using chlorofluorocarbons. These tracers indicate that the river is gaining, due to groundwater discharge in the headwater catchment both in the dry and rainy seasons. Residence time estimation of groundwater using chlorofluorocarbons data reveals that groundwater flow in the shallow sedimentary aquifer is dominated by the binary mixing of water approximating a piston flow model along 2 flow paths: old water, carried by a regional flow system along the direction of river flow, along with young water, which enters the river through local flow systems from hilly areas adjacent to the river valley (particularly during the rainy season). The larger mixing ratio of young water from lateral groundwater recharge and return flow of irrigation during the rainy season result in higher ion concentrations in groundwater than in the dry season. The binary mixing model showed that the ratio of young water versus total groundwater ranged from 0.88 to 0.22 and 1.0 to 0.74 in the upper and lower reaches, respectively. In the middle reach, meandering stream morphology allows some loss of river water back into the aquifer, leading to increasing estimates of the ratio of young water (from 0.22 to 1). This is also explained by declining groundwater levels near the river, due to groundwater extraction for agricultural irrigation. The switch from a greater predominance of regional flow in the dry season, to more localized groundwater flow paths in the wet season is an important groundwatersurface water

The biogeochemical composition of stream water and the surrounding riparian water is mainly defined by the exchange of water and solutes between the stream and the riparian zone. Short-term fluctuations in near stream hydraulic head gradients (e.g., during stream flow events) can significantly influence the extent and rate of exchange processes. In this study, we simulate exchanges between streams and their riparian zone driven by stream stage fluctuations during single stream discharge events of varying peak height and duration. Simulated results show that strong stream flow events can trigger solute mobilization in riparian soils and subsequent export to the stream. The timing and amount of solute export is linked to the shape of the discharge event. Higher peaks and increased durations significantly enhance solute export, however, peak height is found to be the dominant control for overall mass export. Mobilized solutes are transported to the stream in two stages (1) by return flow of stream water that was stored in the riparian zone during the event and (2) by vertical movement to the groundwater under gravity drainage from the unsaturated parts of the riparian zone, which lasts for significantly longer time (> 400 days) resulting in long tailing of bank outflows and solute mass outfluxes. We conclude that strong stream discharge events can mobilize and transport solutes from near stream riparian soils into the stream. The impact of short-term stream discharge variations on solute exchange may last for long times after the flow event.

Rapid groundwater depletion from the northwestern Indian aquifer system in the western Indo-Gangetic basin has raised serious concerns over the sustainability of groundwater and the livelihoods that depend on it. Sustainable management of this aquifer system requires that we understand the sources and rates of groundwater recharge, however, both these parameters are poorly constrained in this region. Here we analyse the isotopic (δ18O, δ2H and tritium) compositions of groundwater, precipitation, river and canal water to identify the recharge sources, zones of recharge, and groundwater flow in the Ghaggar River basin, which lies between the Himalayan-fed Yamuna and Sutlej River systems in northwestern India. Our results reveal that local precipitation is the main source of groundwater recharge. However, depleted δ18O and δ2H signatures at some sites indicate recharge from canal seepage and irrigation return flow. The spatial variability of δ18O, δ2H, d-excess, and tritium reflects limited lateral connectivity due to the heterogeneous and anisotropic nature of the aquifer system in the study area. The variation of tritium concentration with depth suggests that groundwater above c. 80 mbgl is generally modern water. In contrast, water from below c. 80 mbgl is a mixture of modern and old waters, and indicates longer residence time in comparison to groundwater above c. 80 mbgl. Isotopic signatures of δ18O, δ2H and tritium suggest significant vertical recharge down to a depth of 320 mbgl. The spatial and vertical variations of isotopic signature of groundwater reveal two distinct flow patterns in the aquifer system: (i) local flow (above c. 80 mbgl) throughout the study area, and (ii) intermediate and regional flow (below c. 80 mbgl), where water recharges aquifers through large-scale lateral flow as well as vertical infiltration. The understanding of spatial and vertical recharge processes of groundwater in the study area provides important base-line knowledge for developing a sustainable groundwater management plan for the northwestern Indian aquifer system.

Stepwise hydrochemical and isotope-based methodology was adopted to identify mineralization processes, assess the impact of resources overexploitation and flood irrigation, and conceptualize ground...

This article attempts to understand the evolution of groundwater chemistry in the mid Gangetic floodplain through the identification of hydrogeochemical processes including the impact of surface recharge and geological features. Isotopic investigations identified that irrigation return flow is partly responsible for arsenic (As) enrichment through preferential vertical recharge. Further, the floodplain geomorphological attributes and associated As hydrogeochemical behaviour traced through isotopes tracers highlighted that meandering and ox-bow like geomorphological features owing to clay deposition leads to the anoxic condition induced reductive microbial dissolution of As-bearing minerals causing the arsenic contamination in the investigated aquifer of the mid-Gangetic plain (MGP). To achieve the objectives, 146 water samples for water chemistry and 62 samples for the isotopic study were collected from Bhojpur district, Bihar (district bounded by the river Ganges in the north and Son in the east) located in MGP during the pre-monsoon season of 2018. The chemical results revealed high arsenic concentration (BDL to 206 μg.L−1, 32% samples are exceeding the 10 μg.L−1 limit) in the Holocene recent alluviums which are characterized by various geomorphological features such as meander scars and oxbow lake (northern part of the district). Arsenic is more concentrated in the depth range of 15–40 m below ground surface. All other trace metals viz. Ni, Pb, Zn, Cd and Al were found in low concentration except Fe and Mn. The geochemical analyses suggest that rock-water interaction is controlling the hydro-geochemistry while the chemical constituent of the groundwater is mainly controlled by carbonate weathering with limited contribution from silicate weathering. The isotopic signatures revealed that the Son river is recharging groundwater while the groundwater is contributing to the Ganges river. A clear pattern of fast vertical recharge in the arsenic contaminated area is observed in the proximity to the river Ganges with an elevated nitrate concentration resulted from the reduced As dissolution. The origin of groundwater is local precipitation with low to high evaporation enrichment effect which is further indicating the vertical mixing of groundwater from the irrigation return flow and/or recharge from domestic discharge causing enhanced As mobilization through microbial assisted reductive dissolution of As-bearing minerals.

The Singanallur Sub-basin is one of the major waterways and it supplies water to the Coimbatore city. Currently, it is vulnerable to pollution due to an increase of unplanned urban developments, industrial, and agricultural activities that compromise both the quality and quantity. In the present study three major hydrochemical facies were identified (mixed Ca-Mg-Cl, Ca-Cl, and Ca-HCO3). Irrigation suitability indexes are specifies that the groundwater in the areas has very high salinity hazard and low to medium alkali hazard. The mechanism controlling groundwater chemistry originally regulated by the evaporation process is dominated by reason of arid condition and anthropogenic activities existing throughout the region. The multivariate statistical analysis (Correlation analysis (CA), principal component analysis (PCA) and Hierarchical cluster analysis (HCA)) indicates, most of the variations are elucidated by the anthropogenic pollutant predominantly due to population growth, industrial effluents, and irrigation water return flow. This study demonstrates enhanced information of evolution of groundwater quality by integrating hydrochemical data and multivariate statistical methods are used to understand the factors influencing contamination due to natural and anthropogenic impacts.

The present study was carried out for the quantitative assessment of groundwater resource potentials in East Bokaro Coalfield of Damodar River Basin. The rise and fall of groundwater table is closely related to the hydro-meteorological conditions, water level, landform, geology and morphological factors. Average annual rainfall for the entire period of 35 years is 1366 mm in which annual maximum rainfall was 2544 mm in the year 2001 and minimum was 733 mm in the year 2004. The fluctuation of groundwater level ranged between 0.15 and 2.87 mbgl in the study area. Rainfall is the main source to replenish the groundwater by percolation through deep soil zones. Besides rainfall, the mine water discharges from the local mining areas and existing water bodies including water logged in abundant mine quarries. Mine water also contributed to the groundwater recharge as return flow. The study area is highly disturbed and the permeabilities of individual geological units are spatially variable and depend on lithology, fracturing and attenuation with depth. The total annual replenishable recharge was calculated to be 48.5 million m3/year and net annual groundwater availability was estimated to be 13.7 million m3 by rainfall infiltration method. The stage of groundwater development was calculated as per GEC-1997 guideline, which falls under the safe category (i.e., 67%). But water resource conservation for sustainable water management is urgently required in the study area.