Recharge Mechanisms Research Articles

Influence of Sub-Cloud Secondary Evaporation and Moisture Sources on Stable Isotopes of Precipitation in Shiyang River Basin, Northwest China

Fractionation of stable isotopes in precipitation runs through the water cycle, and deuterium excess is a second-order parameter linking water-stable oxygen and hydrogen isotopes. It is strongly influenced by under-cloud evaporation in unsaturated air, especially in arid climates. Based on the improved Stewart model, this study used 670 precipitation stable isotope data and measured meteorological element data from 11 sampling points from January 2018 to September 2019 to verify the existence of sub-cloud secondary evaporation in the Shiyang river basin and quantitatively calculate the intensity of sub-cloud secondary evaporation and its influence on precipitation stable isotopes. The study used the vapor flux and the improved Lagrangian model to track the moisture source of precipitation and analyze the influence of the moisture source of different paths on the stable isotopes of precipitation. Therefore, this study is helpful to understand the evapotranspiration loss mechanism and recharge mechanism of moisture in the watershed. The results showed that there is sub-cloud secondary evaporation in the Shiyang River Basin, and from the seasonal scale, the sub-cloud secondary evaporation is stronger in spring and summer, but weaker in autumn and winter, which makes heavy isotopes enriched in spring and summer and depleted in autumn and winter. From the perspective of spatial distribution, the sub-cloud secondary evaporation is stronger in the midstream and downstream of the Shiyang river, resulting in more enrichment of heavy isotopes. In the vertical direction, the sub-cloud secondary evaporation at 850–700 hPa is the strongest, which enriches the heavy isotope in this layer and reduces the deuterium excess. In addition, the main moisture source of precipitation in the Shiyang River Basin is the westerly air mass, and the mid and high-latitude land sources contribute more moisture to the precipitation. However, the supply of the sea source is very limited, which makes the deuterium excess of precipitation higher and does not show regional consistency and seasonality well.

Understanding the lithium–sulfur battery redox reactions via operando confocal Raman microscopy

The complex interplay and only partial understanding of the multi-step phase transitions and reaction kinetics of redox processes in lithium–sulfur batteries are the main stumbling blocks that hinder the advancement and broad deployment of this electrochemical energy storage system. To better understand these aspects, here we report operando confocal Raman microscopy measurements to investigate the reaction kinetics of Li–S redox processes and provide mechanistic insights into polysulfide generation/evolution and sulfur deposition. Operando visualization and quantification of the reactants and intermediates enabled the characterization of potential-dependent rates during Li–S redox and the linking of the electronic conductivity of the sulfur-based electrode and concentrations of polysulfides to the cell performance. We also report the visualization of the interfacial evolution and diffusion processes of different polysulfides that demonstrate stepwise discharge and parallel recharge mechanisms during cell operation. These results provide fundamental insights into the mechanisms and kinetics of Li–S redox reactions.

The Role of Hydrogeological Monitoring in a Multidisciplinary Context for the Preservation of the Critical Zone in the Natural Reserve of Castelporziano Estate

Critical Zone (CZ) science has developed in recent years, involving different disciplines that vary depending on the specific research focus. This multidisciplinary approach highlights the relevance of the Underground component of the Critical Zone (UCZ) in regulating the water cycle, which can influence the complex equilibrium of the whole CZ. In this study, we analyze evolution during the time of different parameters, characterizing the saturated and unsaturated parts of the UCZ of the Castelporziano Estate, a natural reserve located in a coastal area close to Rome. The purposes of these activities are to monitor the potential depletion of groundwater resources and understand the recharge mechanism processes characterizing the aquifer in the framework of occurring climate changes, net of anthropogenic pressure. The long-term analyses of water table variations carried out over the last 25 years, allowed us to preliminarily identify four different ranges of the slope coefficient of the water table, characterizing different areas of the Estate. Specifically, the Northern, Central, and Coastal areas have shown a general depletion trend in piezometric levels, while in the Eastern area, a positive trend has been recognized. Additional long-term analysis of piezometric level variations allowed us to confirm the presence of the four recharge areas and compare annual recharge and water table levels to assess the relationship between the saturated UCZ and meteoric recharge in the identified areas. To evaluate the role of the unsaturated UCZ in recharge mechanisms, the water content in the first meter of soil has also been analyzed, showing different responses of outcropping sediments in capturing rainfall during different periods of the year and under different rainfall input conditions, highlighting the pivotal role of rainfall for the Castelporziano UCZ, both for deep recharge of the water table and for feeding the forest roots. Stable isotopes confirm that Castelporziano UCZ feeding is strongly dependent on local meteoric recharge, also highlighting that evaporation processes are active in a limited way. The obtained results assess that the monitoring of UCZ has a crucial role in the correct preservation of more complex environmental systems, which include groundwater resources and the coastal Mediterranean forest.

Understanding mechanisms of recharge through fractured sandstone using high-frequency water-level-response data

Understanding mechanisms of recharge through fractured sandstone using high-frequency water-level-response data

Significance of river infiltration to the Port-au-Prince metropolitan region: a case study of two alluvial aquifers in Haiti

Mountain block recharge (MBR) mechanisms are an important component of the water budget for many alluvial aquifers worldwide. The MBR dynamics are complex, difficult to constrain, and quantification is highly uncertain. These challenges are magnified in data-scarce study areas, including the Cul-de-Sac and Leogane plains, two of Haiti’s largest alluvial aquifers, which are flanked by the Massif de la Selle mountain block. The associated groundwater supplies the regional metropolitan area of Port-au-Prince (RMPP) and it is facing increasing pressure, requiring improved understanding of the aquifer system to guide management and protection. This report introduces the aquifers and investigates the significance of river infiltration from flows originating from the mountain block. The approach to derive important insight on recharge included analysis of broad datasets on piezometry, isotopes, hydrochemistry, and streamflow. The findings indicate that river infiltration is a major source of recharge to the alluvial aquifers. Grise and Blanche river infiltration may account for >80% of recharge to the Cul-de-Sac aquifer, exhibiting temporal variation correlated to climate events such as cycles of the El Niño/La Niña Southern Oscillations. Momance and Rouyone river infiltration may account for >50% of recharge to the Leogane aquifer. The results direct attention to the Massif de la Selle carbonate aquifer system, where bulk recharge is estimated to be four times greater than both alluvial aquifers. The Massif not only supplies the RMPP with ~65% of its water supply from karst springs, but its streamflow also recharges the alluvial aquifers that supply the balance of RMPP supply.

The Inskie Springs: New Insights into Low-Radon Waters

Abstract —In August 2019, four descending (gravity) springs in the Inya River valley were sampled during the field works conducted within the study of low-radon waters of the Novosibirsk urban agglomeration in the area lying away from known granite massifs. Laboratory analyses have revealed enhanced radon activity concentrations (from 5 to 149 Bq/dm3). It has been established that these waters are fresh, of HCO3 Mg–Ca chemical composition, and have a TDS value of 413 to 548 mg/dm3 and a silicon content of 4.1–8.6 mg/dm3. They are characterized by neutral to slightly alkaline pH (7.1–8.4) and oxidizing geochemical conditions with Eh from +205.3 to +231.8 mV and O2 dissolv. = 6.24–12.26 mg/dm3. The revealed predominance of SO42– over Cl– concentrations in the waters of the study area was probably due to the presence of sulfides in the water-bearing sediments, in particular, pyrite in the surface sediments. More than tenfold proportional excess of Ca concentrations over Si in the Inskie spring waters indicates the predominantly carbonate composition of the water-bearing sediments. The gross α-activity of waters is 3–4 mBq/dm3, and gross β-activity is 11–15 mBq/dm3. Natural radionuclides are found in the spring waters within the following limits (mg/dm3): 238U, from 2.83 ∙ 10–3 to 4.13 ∙ 10–3; 232Th, from 2.39 ∙ 10–6 to 1.16 ∙ 10–5, and 226Ra, from 3.83 ∙ 10–10 to 4.93 ∙ 10–10. The value of the 232Th/238U ratio for the waters ranges from 5.79 ∙ 10–4 to 3.61 ∙ 10–3, as a result of the oxidative geochemical migration-arresting capability of thorium. The uranium isotope ratio (γ) 234U/238U varies from 2.6 to 3.2 for the waters, with the uranium isotope activity determined as 117–124 mBq/dm3 for 234U and 38–48 mBq/dm3 for 238U. This indicates shallow circulation of the studied waters as compared with those of the Svyatoi spring in Verkh-Tula Village, for which γ = 1.3; the 234U activity, 147 mBq/dm3; and the 238U activity, 115 mBq/dm3. By isotopic composition, the origin of the spring waters is assigned to the infiltration type, and they are characterized by relatively narrow distribution of δ18O (from –17.5 to –16.7‰) and δD (from –128.4 to –126.2‰) values. The δ13CDIC values are from –10.3 and –10.9‰ in springs 3 and 2 and become lighter (–11.2 and –12.1‰) in springs 1 and 4, respectively. This is due to significant participation of surface waters in the recharge mechanism of springs 1 and 4, which is also consistent with the δ18O and δD data and 14C dating. The estimated age of water-dissolved carbon is 1478 ± 81 years for the waters of spring 3 (the oldest), while it is found to be only 651 ± 53 years for spring 4 and is estimated as modern for spring 1. The reported decline in the age of water-dissolved carbon down to recent age is indicative of increased contribution of surface water to the spring recharge area. The C and O isotope compositions of calcite of the host aquifer rocks are characterized by close values for most of the samples: δ13С varies within narrow limits (from –3.1 to –2.7‰), and δ18О varies from 17.2 to 18.4‰. The isotopic composition becoming lighter for carbon (up to –11.0‰) and oxygen (up to 13.9‰) was noted for weathered schist samples. Results of the carbon isotope analysis of rock samples, their organic component, and water indicate an active isotopic exchange in the water–rock–organic matter system.

Interaction Simulation of Vadose Zone Water and Groundwater in Cele Oasis: Assessment of the Impact of Agricultural Intensification, Northwestern China

Agricultural intensification has boosted land productivity, but it has also created new sustainability issues. As one of the most important human habitations and agricultural farming areas in arid areas, the Cele Oasis has a very developed agricultural system. This paper studies the long-term effects of different types of agricultural intensification strategies on groundwater level fluctuations in the Cele Oasis. A soil water flow (HYDRUS-1D) and aquifer simulation (MODFLOW) coupling model were used to construct the geometric structures of the vadose zone and saturated zone in the Cele Oasis and to analyze the recharge and discharge mechanism of the oasis. The results showed that HYDRUS-1D accurately simulated soil moisture transport in the Cele Oasis, providing reliable data for calibration of the MODFLOW model. The groundwater level simulated by MODFLOW was in good agreement with the observed value. The results of the R2, RMSE, and NSE were ranges of 0.77–0.90, 0.45–0.74 m, and 0.76–0.87, respectively. The errors were acceptable limits. The coupling model predicted the responses of different agricultural types and cropping scenarios to groundwater. Predictions showed that the groundwater level in the Cele Oasis remained stable under the current cropping scenario (100% cropping intensity), and that the groundwater level decreased slightly under the cropping scenario (110% cropping intensity and 130% cropping intensity). When the cropping scenario was at 170% cropping intensity, the groundwater level decreased rapidly, and the maximum drawdown value was 7 m. Therefore, the maximum cropping intensity of the Cele Oasis in the future should be 130% of the current cropping intensity.

Understanding recharge mechanisms and surface water contribution to groundwater in granitic aquifers, Ghana: Insights from stable isotopes of δ2H and δ18O

In hydrological studies, the use of stable isotopes (δ18O and δ2H) of water has proven to be a powerful tool to study groundwater recharge and mixing dynamics, which are critical to the long-term management of groundwater resources. In this study, we analyzed the stable isotopes of rain (event basis), groundwater (boreholes and hand-dug wells) and surface water in the White Volta River basin (Ghana). The aim is to understand the groundwater recharge processes, quantify the contribution of surface water to groundwater and assess the feasibility of artificial recharge in an agricultural catchment area. The results show that the event-based δ18O showed a weak dependence on air temperature (T) and rainfall (P) amount, while the monthly weighted average showed a much stronger correlation. The δ18O and δ2H show that rainfall is the main source of recharge and occurs in events greater than 10 mm. Overall, most of the groundwater falls between the June, July and August rains, suggesting that these months represent the recharge period. The groundwater isotopic variability is mainly influenced by local recharge and mixing with surface water. Low δ18O and high d-excess were found in most of the groundwater samples in the basin, indicating recent recharge conditions. The isotope mixing model shows that the surface water contribution to groundwater recharge is extremely variable, ranging from 1.47 ± 0.09% to 51.69 ± 6.04% suggesting the potential for artificial recharge. To summarize our results on the dynamics of groundwater recharge in the catchment area, we have provided a conceptual framework of our results.

Isotopic composition of groundwater resources in arid environments

The availability and quality of limited groundwater resources in Egypt are negatively affected by both natural and anthropogenic forces. It is crucial to understand the recharge sources and mechanisms of country-scale aquifers in order to develop sustainable management scenarios for Egypt's groundwater resources. In this study, we compiled all historical hydrogen (δ2H) and oxygen (δ18O) stable isotopic compositions of 1618 ground- and surface-water samples collected for seven major aquifer and reservoir systems in Egypt. These data were then hosted in a public-domain web map application (https://bit.ly/3n9MtrM) that enables users to access, navigate, display, and analyze the isotopic composition of any water sample in Egypt. The developed application and customized web tools were then used to provide improved understanding of the country-wide water resources’ isotopic composition and to investigate the recharge sources and mechanisms of, and provide sustainable management scenarios for, the seven major Egyptian aquifer systems. Results indicate that (1) the alluvial and coastal aquifers are recharged from modern rainfall, floodwaters, and upward leakage from deep aquifers; (2) the Nile Valley and Delta, Moghra, and carbonate aquifers are receiving recharge from the Nile River, modern rainfall, irrigation canals and drains, and upward leakage from deep aquifers; (3) the Nubian aquifer receives modern recharge in areas of higher rainfall or close to surface water reservoirs; and (4) the fractured basement aquifers are recharged from modern rainfall and floodwaters. The developed cost-effective web application will guide locations and techniques for future field data collection; reduce time, efforts, and resources required for field activities; enable improved understanding the country-wide stable isotopic compositions of water resources; enhance understanding of nationwide recharge mechanisms; and enable the scientific community to address country-scale science questions in a unique way.

Deciphering complex groundwater age distributions and recharge processes in a tropical and fractured volcanic multi‐aquifer system

AbstractGroundwater recharge in highly fractured volcanic aquifers in the humid tropics remains poorly understood. In this region, rapid demographic growth and unregulated land use change are resulting in extensive surface water pollution and a large dependency on groundwater extraction. Here we present a multi‐tracer approach including δ18Oδ2H, 3H/3He dating, and noble gases (NG) within the most prominent multi‐aquifer system of central Costa Rica, with the objective to assess dominant groundwater recharge mechanisms and age distributions. We sampled wells and large springs across an elevation gradient from 868 to 2421 m asl. Our results indicate relatively young apparent ages ranging from 0.0 ± 3.2 up to 43.5 ± 7.6 years within the unconfined aquifer system. Helium isotopes (R/Ra up to 5.4) indicate a dominant signal from the upper mantle and preclude 3H/3He dating in 50% of the samples. Potential recharge elevations (based on NG and δ18O) ranged from ~1350 to 2670 m asl. NG‐derived recharge temperatures ranged from 11.0°C to 19.4°C. Recharge estimates varied from 129 ± 78 to 1605 ± 196 mm/yr with a mean value of 642 ± 117 mm/yr, representing 20.1 ± 4.0% of the total mean annual rainfall as effective recharge. The shallow unconfined aquifer is characterized by young and rapidly infiltrating water, whereas the deeper aquifer units have relatively older water (>60 years). These results are intended to guide the delineation and mapping of critical recharge areas in mountain headwaters to enhance water security and sustainability in the most important headwater dependent systems of Costa Rica.

Characterizing Recharge in Southern Mali Using a Combination of Modeling and Stable Isotopes

Groundwater recharge in southern Mali is investigated using interpretive recharge models and stable isotopes to identify the dominant recharge mechanism and explore how local variations in geological materials influence the recharge characteristics. At a regional scale, the groundwater level hydrographs from across southern Mali (1998–2002) are relatively consistent, showing seasonal variations, suggesting diffuse recharge is the dominant mechanism. Groundwater samples plot within the range of the weighted mean monthly δ18O and δ2H concentrations for July-August-September rainfall, and below the weighted mean annual δ18O and δ2H concentrations for rainfall, suggesting a dominantly rainy season source of recharge. Recharge is simulated for four representative unsaturated zone environments, each with varying soil, laterite and sedimentary bedrock layers, and three ranges of water table depths, for a total of 12 combinations. The simulated recharge response starts in July, 1 month after the arrival of the rainy season, and recharge is greatly accelerated through August to its peak in September. On an annual basis, ~72% of annual rainfall occurs between July and September, and nearly 60% of simulated recharge occurs between August and October. The simulated regional average annual recharge is 519 mm/year (479–560 mm/year range among models). By comparison, recharge estimated from the observed storage anomaly hydrographs using the water table fluctuation method is 384 mm/year (189–619 mm/year) using a specific yield of 0.05, although the range could be as high as 83–772 mm/year given the uncertainty in specific yield values (0.02–0.07). The simulated recharge also agrees with the timing of regional observed storage anomalies for all observation wells, but somewhat less so for the regional GRACE storage anomaly (2002–2008), which has a slower rate of rise in storage and a faster rate of recession compared to the observed storage anomalies and simulated recharge response.

Isotopic and Chemical Tracing for Residence Time and Recharge Mechanisms of Groundwater under Semi-Arid Climate: Case from Rif Mountains (Northern Morocco)

Karstic aquifers play an important role for drinking and irrigation supply in Morocco. However, in some areas, a deeper understanding is needed in order to improve their sustainable management under global changes. Our study, based on chemical and isotopic investigation of 67 groundwater samples from the karst aquifer in the Rif Mountains, provides crucial information about the principal factors and processes influencing groundwater recharge and residence time. The δ18O and δ2H isotopic values indicate that the recharge is derived from meteoric water at high, intermediate, and low elevations for Lakraa Mountain, North of Lao River, and Haouz and Dersa Mountain aquifers, respectively. All samples show an isotopic signature from Atlantic Ocean except for those from the Lakraa Mountain aquifer, which shows Mediterranean Sea influence. Groundwater age determined by radiocarbon dating using the IAEA model indicates that the ages range from modern to 1460 years. This short residence time is consistent with the detectable tritium values (>2.7 TU) measured in groundwater. These values are similar to those of precipitation at the nearest GNIP stations of Gibraltar and Fez-Saiss, situated around 100 km north and 250 km south of the study area, respectively. This evidence indicates that groundwater in the Rif Mountains contains modern recharge (<60 years), testifying to significant renewability and the vulnerability of the hydrological system to climate variability and human activities. The results also indicate the efficiency of isotopic tracing in mountainous springs and would be helpful to decision makers for water in this karstic zone.

Stable isotope and geochemical evidence on sources and mechanisms of groundwater recharge in the Nalanda-Rajgir Region of Eastern India

Stable isotope and geochemical evidence on sources and mechanisms of groundwater recharge in the Nalanda-Rajgir Region of Eastern India

Insights into oil recovery mechanism by Nothing-Alternating-Polymer (NAP) concept

This paper introduces new oil recovery mechanisms for oil recovery by polymer injection in heavy oil reservoirs with strong bottom aquifers. Due to unfavorable mobility ratio between aquifer water and oil and the development of the sharp cones significant amount of oil remains unswept. To overcome these issues, for the case demonstrated in this paper, a polymer injection pilot was executed with three horizontal injectors, located a few meters above the oil/water contact. The injectivity issues resulted in frequent shutdowns of the injectors. Interestingly, the water cut reversal and oil gain continued during the shut-in periods. This observation has led to the development of a new cyclic polymer injection strategy, in which the injection of polymer is alternated with intentional well shut-ins. The strategy is referred to as Nothing-Alternating-Polymer (NAP).It was found that during polymer injection, the oil is recovered by conventional mobility and sweep enhancement mechanisms ahead of the polymer front. Additionally, during this stage the injected polymer squeezes the existing cones and creates a barrier between the aquifer and the oil column, suppressing the aquifer flux and hence the negative effect of the cones or water channels (blanketing mechanism). Moreover, injection of polymer pushes the oil to the depleted water cones, which is then produced by the water coming from the aquifer during shut-in period (recharge mechanism). During the shut-in or NAP period, the aquifer water also pushes the existing polymer bank and hence leads to extra oil production. The resistance caused by polymer adsorption reduces the extent of fingering of water into polymer bank. The NAP strategy reduces polymer loss into aquifer and improves the polymer utilization factor expressed in kg-polymer/bbl of oil, resulting in a favorable economic outcome.

Recharge mechanism and salinization processes in coastal aquifers in Nam Dinh province, Vietnam

In Nam Dinh province, in the Red River delta plain in Northern Vietnam, groundwater in the shallow Holocene aquifer shows elevated total dissolved solids up to 35 km from the coastline, indicating a saltwater intrusion from the Gulf of Tonkin. High groundwater salinities have been encountered below and adjacent to the Red River in the deep Pleistocene aquifer. Since 1996, large-scale groundwater abstraction was initiated from the deep aquifer, and the observed elevated salinities now raise concerns about whether the groundwater abstraction is undertaken sustainably. We have conducted a study to obtain a fundamental understanding of the recharge mechanisms and salinization processes in the Nam Dinh province. A holistic approach with multiple methods including transient electromagnetic sounding and borehole logging, exploratory drilling, sampling and analyzing primary ion and stable isotope compositions of water and pore water, groundwater head monitoring, hydraulic experiments laboratory of clay layers, and groundwater modeling by using the SEAWAT code. Results reveal that saline river water is leached from the Red River and its distributaries into the shallow aquifers. The distribution and occurrence of salty pore water in the Holocene aquitard clay shows that meteoric water has not been flowing through these low permeable clay layers. Marine pore water has, however, been leached out of the Pleistocene clay. When this layer is present, it offers protection of the lower aquifer against high salinity water from above. Salinity as high as 80 % of oceanic water is observed in interstitial pore water of the transgressive Holocene clay. Saltwater is transported into the Pleistocene aquifer, where the Holocene clay is directly overlying the aquifer.

ВИКОРИСТАННЯ ЧАСОВОГО ТА ПРОСТОРОВОГО РОЗПОДІЛУ ТРИТІЮ ДЛЯ ІНДИКАЦІЇ ЗМІН СТАНУ СЕНОМАН-КЕЛОВЕЙСЬКОГО КОМПЛЕКСУ ПИТНИХ ПІДЗЕМНИХ ВОД НА ТЕРИТОРІЇ МІСТА КИЄВА

The presented research is devoted to study and establishment of the spatiotemporal change of tritium content in groundwater of CenomanianCallovian groundwater complex in Kyiv and the causes of these changes in order to identify water exchange features and hydraulic interaction between shallow and deep aquifers, as well as between groundwater and surface waters. Due to the excessive use of groundwater, depressive surfaces of hydrodynamic pressures have formed, aquifers are transforming from pressure head to pressureless, and there is a danger of downward filtration and contamination of potable groundwater. Also, one of the effects of these depressions formation is deterioration of water quality. However, to study the conditions of the qualitative composition formation of deep potable aquifers and to identify the causes of changes in groundwater status is a difficult and responsible task at the same time. Methods of isotopic hydrogeology are among the main scientific methods used to track the peculiarities of groundwater movement and assess their age. The new data obtained by isotopic methods help to control water resources and allow to make such decisions that will bring socio-economic benefits. The obtained data of tritium content in groundwater of Cenomanian-Callovian groundwater complex, clearly presented in the form of maps, allow to make informed decisions on sustainable resource management, and regular monitoring of chemical and isotopic composition of groundwater reveals mechanisms of recharge and sources of pollution, which were not taken into account before. The results obtained by the authors through statistical and spatial analysis of tritium content in groundwater during 2014-2017, indicate that currently within the territory of Kyiv there is a positive trend towards a slow gradual return of Cenomanian-Callovian groundwater complex to its natural state.

The Relationship Between Morpho-structural Features and Borehole Yield in Ilesha Schist Belt, Southwestern Nigeria: Results from Geophysical Studies

Aeromagnetic data and Landsat image, were assessed to establish a relationship between morphostructural feature and borehole yield of a sub-basin of Osun basin in the Northern part of Ilesha, southwestern Nigeria. Four morphostructural factors (Geomorphological unit, Slope, regional structure, and lineament) were considered. Geomorphological units were classified based on digital elevation model (DEM), Lineaments were identified and extracted using edge detection technique, slope were generated from the digital data derived from Landsat imagery, and the regional structure were extracted using magnetic data filtering and enhancement techniques processes. The results of morphostructural features shows five (5) various geomorphic units; (Denudation hill, linear ridge, pediment inselberg complex, pediment and moderately weathered Pediplain) and four (4) main structural trends (NE-SW, NW-SE, ENE-WSW and E-W directions). The relationship between the morphostructural factors and borehole yield were assessed using spatial global autocorrelation and spearman rank correlation. Moran’s I global tests for dependence shows that geomorphological units, and regional structures were clustered given the z-scores of 2.46 and 1.99, p-values of 0.01 and 0.04, Moran’s I index value of 0.08 and 0.06 respectively. Likewise, borehole yield, lineament and slope were dispersed given the z-scores of 0.89, -0.43 and -1.15, p-values of 0.38, 0.66 and 0.25, Moran’s I index value of -0.06, -0.04 and -0.07 respectively. The Spearman’s rank correlation for the four independent variables (Geomorphological unit, Slope, Fracture, and Lineament) are statistically significant to the observed borehole yield, with correlation coefficients of -0.332, 0.137, -0.031, 0.200 respectively. The study concluded that slope and lineament are capable of favoring high borehole yield indicative of active surface recharge mechanism that is prominent in Schist belts and regional structures have little or no contribution to borehole yield in schist belts due to the influence of developed clayey filling resulting from the deep weathering processes.

Groundwater Recharge Assessment Using Multi Component Analysis: Case Study at the NW Edge of the Varaždin Alluvial Aquifer, Croatia

Exploring the interaction between precipitation, surface water, and groundwater has been a key subject of many studies dealing with water quality management. The Varaždin aquifer is an example of an area where high nitrate content in groundwater raised public concern, so it is important to understand the aquifer recharge for proper management and preservation of groundwater quality. The NW part of the Varaždin aquifer has been selected for study area, as precipitation, Drava River, accumulation lake, and groundwater interact in this area. In this study, groundwater and surface water levels, water temperature, water isotopes (2H and 18O), and chloride (Cl−) were monitored in precipitation, surface water, and groundwater during the four-year period to estimate groundwater recharge. Head contour maps were constructed based on the groundwater and surface water levels. The results show that aquifer is recharged from both Drava River and accumulation lake for all hydrological conditions–low, mean, and high groundwater levels. The monitoring results of water temperature, chloride content, and stable water isotopes were used as tracers, i.e. as an input to the mixing model for estimation of the contribution ratio from each recharge source. The calculation of mixing proportions showed that surface water is a key mechanism of groundwater recharge in the study area, with a contribution ratio ranging from 55% to 100% depending on the proximity of the observation well to surface water.

Deep groundwater recharge mechanism in the sedimentary and crystalline terrains of Sri Lanka: A study based on environmental isotope and chemical signatures

Springs discharge groundwater that travels along flow paths of different spatial and time domains. In many instances, it is difficult to describe its involved groundwater movement, availability as well as geochemical evolution due to its hidden nature. The present study has assessed the deep groundwater in the form of thermal and non-thermal springs in the Palavi and Vanathavillu basins of sedimentary terrain as well as the Southern, Eastern, and Eastern-North Central lowlands of the crystalline terrain of Sri Lanka, using isotope and geochemical approaches. The results revealed that cation exchange in the sedimentary aquifers, whereas rock-water interaction in hard rock and fairly deep aquifers, are the important factors that control the groundwater chemistry. Artesian wells in the sedimentary terrain are mainly recharged by meteoric water, moving through fractured basement rocks at elevations from 100 to 200m above sea level, and have a long residence time. Despite its proximity to the West coast, the data acquired do not indicate that there is seawater mixing. Mixing of percolated water through an unconsolidated geological matrix appears to promote an increase in the salinity of groundwater. Non-mixed, non-evaporated, and young groundwater with a recharge elevation of more than 1000 m above mean sea level can be found in the Southern lowlands of the crystalline terrain. In the Eastern North Central lowlands, groundwater is lowland originated, fast replanished and significantly mixed with evaporated surface water. Thermal waters do not contain tritium and therefore are older than 50 years and have deeply percolated. Artesian water in the Eastern region is high altitude originated and intensely rock-water interacted. Some hot springs in the same area emerging through weathered overburden have water significantly mixed with recent precipitation. Thermal springs that emerge through quartzite bedrock have a non-mixed, non-evaporated, and less rock-water interacted nature. Both thermal and non-thermal water with artesian conditions have clearly indicated that they originate from a common recharge source but with different flow paths, penetration depths, and travel distances, resulting in different chemical characteristics. Non-thermal springs are recharged by recent precipitation and have percolated only to shallow depths.

Use of Multidisciplinary Approaches for Groundwater Recharge Mechanism Characterization in Basement Aquifers: Case of Sanon Experimental Catchment in Burkina Faso

In Burkina Faso, the basement aquifers represent a major asset in terms of quantity and quality, for both drinking and irrigation purposes for rural populations. They provide water resources that can guarantee the long-term needs of the populations, provided that a sustainable management policy for these resources is adopted. Yet, any groundwater resource management policy is necessarily linked to a better knowledge of aquifer recharge mechanisms, which is yet to be fully assessed in the Sahelian basement area. The objective of this study was to characterize the recharge mechanism within the experimental site of Sanon, located in the basement zone in Burkina Faso, using a coupling of hydrodynamic and chemical approaches. The hydrodynamic approach consisted of monitoring the spatial and temporal distribution of the piezometric levels of the aquifers along a north–south and east–west transect and determining soil infiltration capacity. The hydrochemical characterization of the aquifers was carried out through an analysis of groundwater samples from the concerned aquifers and daily tracing of the electrical conductivity of the aquifer water. The cross-analysis from the results of the implemented approaches shows a direct recharge mechanism through rainwater infiltration in the central valley, an indirect recharge mechanism in the lowlands, and a recharge mechanism by lateral transfers in the peripheral aquifers of the Sanon experimental catchment. The existence of a piezometric dome reveals in the central valley a zone of preferential recharge and water movement. The water of the central valley is the least mineralized with electrical conductivities below 100 µS/cm. This mineralization follows the direction of the water flow.