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Groundwater resources are vital for water security but face threats from overexploitation, contamination, and climate change. This study focuses on the Guarani (GAS) and Bauru (BAS) aquifer systems' recharge in western São Paulo, Brazil. We enhanced the scalability of the potential recharge (PR) method and assessed recharge using groundwater storage (GWS) data from the Gravity Recovery and Climate Experiment (GRACE). Our findings indicate that while the remote sensing-based PR method aligns with the existing literature, it tends to overestimate recharge. Conversely, the GWS method provides more conservative and reliable estimates. Integrating remote sensing-based methods is a crucial tool for improving recharge estimation and supporting groundwater resource management. [ABSTRACT FROM AUTHOR]

Managed Aquifer Recharge (MAR) has been implemented in the upper alluvial plain of the Chaobai River, significantly affecting the groundwater level and causing it to rise. However, the effects of the MAR on land subsidence,remain largely unknown. To elucidate the effects of MAR on land subsidence, a comprehensive analysis was undertaken, integrating interferometric synthetic aperture radar (InSAR) data, extensometer measurements, and groundwater level observations.Our analysis revealed a discernible land rebound phenomenon, with rates escalating from 2.3 mm/a in 2015 to 20 mm/a in 2021. This rebound extends southwestward, following a dispersion pattern that aligns with pre-existing fault structures, suggesting their controlling influence. The groundwater level changes caused by the MAR can cause land rebound, especially near fault footwalls. However,low permeability in fault zones hinders groundwater flow in the hanging wall resulting in slight land deformation. Lithology also affects rebound, with sandy soils showing more significant land rebound, while low-sand areas exhibit limited or delayed rebound. These findings offer crucial insights into the interplay between MAR, groundwater dynamics, and land subsidence in the studied region. They provide a foundation for informed decision-making in groundwater replenishment strategies and precise subsidence prevention and control measures. Future research should maintain a vigilant monitoring of the long-term consequences of MAR on land subsidence to ensure sustainable regional development. [ABSTRACT FROM AUTHOR]

Abstract Climate change has a significant impact on water resources, making it essential to re-evaluate water management strategies and incorporate climate scenarios in assessments. The Municipal Department of Aigeiros is located in the northern part of Greece. Water consumption is high in Aigeiros and the increased future temperatures projected during the summer period will create significant pressures on water resources. The water resources management study of the region is carried out using the simulations of the RCA4 Regional Climate Model (RCM) driven by the HadGEM-ES global climate model of the Met Office Hadley Centre (MOHC) under 3 different climate emission scenarios, namely RCP 2.6, RCP 4.5 and RCP 8.5. For the simulation of the urban water balance of Aigeiros, Komotini, Greece and the assessment of water demand and supply for three climate scenarios (RCP 2.6, 4.5, and 8.5) over a 30-year period, the Aquacycle software was used. The data used in the assessment included projected climatic conditions for the area (i.e., precipitation and evapotranspiration), domestic water consumption, and natural and spatial characteristics. The results indicate that drinking water demand is likely to increase in the coming decades for RCP 4.5 (1323 m3/d for 2041–2050) and RCP 8.5 (1330 m3/d for 2041–2050) scenarios compared to 2020 (1320 m3/d). However, simulations for water supply suggest an increase in groundwater recharge in the future, but also the potential for long drought periods during summer months in RCP 4.5 and RCP 8.5 scenarios. The simulation results show both the current situation and the climate scenarios and can be the reference basis for recording the different types of water consumption in urban areas. Therefore, it is possible to control and predict how much of the total consumption is due to the consumer usage profile within a household or to the irrigation needs of green areas in line with the climatic conditions, consumer behavior and technical parameters.

Groundwater return flow to streams is important for maintaining aquatic habitat and providing water to downstream users, particularly in irrigated watersheds experiencing water scarcity. However, in many agricultural regions, increased irrigation efficiency has reduced return flows and their subsequent in‐stream benefits. Agricultural managed aquifer recharge (Ag‐MAR)—where artificial recharge is conducted via irrigation canals and agricultural fields—may be a tool to recover these return flows, but implementation is challenged by water supply and water management. Using climate‐driven streamflow simulations, an integrated operations‐hydrology model, and a regional groundwater model, we investigated the potential for Ag‐MAR to recover return flows in the Henrys Fork Snake River, Idaho (USA). We simulated potential Ag‐MAR operations for water years 2023–2052, accounting for both future water supply conditions and local water management rules. We determined that Ag‐MAR operations reduced springtime peak flow at the watershed outlet by 10%–14% after accounting for return flows. Recharge contribution to streamflow peaked in July and November, increasing July–August streamflow by 6%–14% and November–March streamflow by 9%–14%. Furthermore, sites where Ag‐MAR was conducted incidental to flood irrigation had more water available for recharge, compared to sites requiring recharge rights, which are junior in priority to agricultural rights. Mean annual recharge volume for the incidental recharge sites averaged 12% of annual natural streamflow, ranged from 269 to 335 Mm3, and was largely available in April and October. We demonstrate Ag‐MAR can effectively recover groundwater return flows when applied as flood irrigation on agricultural land with senior‐priority water rights. Plain Language Summary: Some water that seeps into the ground follows underground pathways and flows into rivers. This water is called groundwater return flow and is important in water‐scarce regions. Groundwater return flow increases streamflow and provides more water to farms and fish downstream but is decreasing in many agricultural regions. Agricultural managed aquifer recharge (Ag‐MAR) may be a tool to save these return flows. Ag‐MAR uses canals and agricultural fields to artificially increase the amount of water that seeps into the ground, but conducting Ag‐MAR can be difficult during water shortages and/or due to water management rules. We investigated the possibility of using Ag‐MAR to recover return flows in the Henrys Fork Snake River, Idaho (USA), accounting for both future water supply conditions and rules that limit access to water supply. We simulated 30 years of future conditions and found that water for Ag‐MAR is largely available at sites with senior‐priority water rights. We also found that conducting Ag‐MAR reduced peak springtime streamflows by 10%–14% but increased summer streamflow by 6%–14% and winter streamflow by 9%–14%. Thus, Ag‐MAR can effectively recover groundwater return flows in our study area. Key Points: Water was reliably available to conduct agricultural managed aquifer recharge (Ag‐MAR) via flood irrigation with senior‐priority water rights, even in dry yearsWater was available in <30% of years to conduct Ag‐MAR at designated recharge basins with junior‐priority water rightsAg‐MAR generated return flows that increased July–August streamflow by 6%–14% and November–March streamflow by 9%–14% [ABSTRACT FROM AUTHOR]

Managed Aquifer Recharge (MAR) has been implemented in the upper alluvial plain of the Chaobai River, significantly affecting the groundwater level and causing it to rise. However, the effects of the MAR on land subsidence,remain largely unknown. To elucidate the effects of MAR on land subsidence, a comprehensive analysis was undertaken, integrating interferometric synthetic aperture radar (InSAR) data, extensometer measurements, and groundwater level observations.Our analysis revealed a discernible land rebound phenomenon, with rates escalating from 2.3 mm/a in 2015 to 20 mm/a in 2021. This rebound extends southwestward, following a dispersion pattern that aligns with pre-existing fault structures, suggesting their controlling influence. The groundwater level changes caused by the MAR can cause land rebound, especially near fault footwalls. However,low permeability in fault zones hinders groundwater flow in the hanging wall resulting in slight land deformation. Lithology also affects rebound, with sandy soils showing more significant land rebound, while low-sand areas exhibit limited or delayed rebound. These findings offer crucial insights into the interplay between MAR, groundwater dynamics, and land subsidence in the studied region. They provide a foundation for informed decision-making in groundwater replenishment strategies and precise subsidence prevention and control measures. Future research should maintain a vigilant monitoring of the long-term consequences of MAR on land subsidence to ensure sustainable regional development.

Groundwater resources are depleting worldwide owing to climate change and exponential rise in population. In order to manage groundwater resources, consideration must be given to availability of the groundwater and the functioning of the aquifer system. In this regard, the present study aims to explore groundwater potential zones for Guercif, Morocco for highlighting the importance of groundwater resources management. The groundwater potential zones are investigated using multicriteria decision analysis technique in GIS software from perspectives of slope, drainage density, land use landcover, geology, soil type and groundwater levels. As per results, poor groundwater potential zones in the study area were minimum (about 1 km²) followed by excellent (257 km²), fair (632 km²), moderate (2710 km²) and good (6064 km²) groundwater potential zones, respectively. Watershed of the study area has good groundwater potential zones of about 62.75% whereas only 0.01% falls in poor groundwater potential zones. The current research concluded that estimating the groundwater potential zones using GIS and RS remote sensing techniques could saves time and money as compared to the conventional methods. The study is recommended for decisions making and managing the groundwater resources for betterment of the region in future. Therefore, the study provides critical insights for public and government sectors to understand the potential zones for sustainable groundwater utilization and management. [ABSTRACT FROM AUTHOR]

Coordinating management of groundwater, surface water, and irrigated crops is fundamental economically for many arid and semi-arid regions. This paper examines conjunctive water management for agriculture using hydro-economic optimization modeling. The analysis is integrated across two timescales: a two-stage stochastic decadal model for managing annual and perennial crops spanning dry and wet years and a far-horizon dynamic program embedding the decadal model into a longer groundwater policy setting. The modeling loosely represents California's San Joaquin Valley and has insights for many irrigated arid and semi-arid regions relying on groundwater with variable annual hydrology. Results show how conjunctive water management can stabilize crop decisions and improve agricultural profitability across different water years by pumping more in dry years and increasing recharging groundwater in wetter years. Using groundwater as a buffer for droughts allows growing more higher-value perennial crops, which maximizes profit even with water-scarce conditions. Nevertheless, ending overdraft in basins with declining groundwater for profit-maximizing farming reduces annual crops to maintain more profitable perennial crops through droughts. Results are affected by economic discount rates and future climates. Operating and opportunity costs from forgone annual crops can reduce aquifer recharge early in regulatory periods. [ABSTRACT FROM AUTHOR]

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Spatial and temporal variations of the water table could be explained by the one-dimensional Boussinesq equation by incorporating the variables of evapotranspiration and groundwater recharge with appropriate initial and boundary conditions. In this study, the stream–aquifer interaction has been investigated through a numerical example model with the implementations of Galerkin's method-based Finite Element Solution (FES), Hybrid Finite Analytic Solution (HFAS), Fully Implicit Finite Difference Solution (FIFDS) of one-dimensional nonlinear Boussinesq equation, and analytical solutions of the Boussinesq equation linearized by Baumann's transformation (AS I) as well as linearized by Werner's transformation (AS II). Considering HFAS as the benchmark solution, it was observed that in both recharging and discharging aquifers, water table profiles at 1 day and 5 days as obtained from FES followed by FIFDS were observed quite close to HFAS. Based on L2 and Tchebycheff norms, FES and FIFDS were ranked in first and second place, respectively. L2 and Tchebycheff norms could not consistently establish the performance ranking of analytical solutions but their performance ranking was certainly below the numerical solutions. The performance ranking of analytical solutions could not consistently be established using the L2 and Tchebycheff norms, but it was certainly below the numerical solutions. HIGHLIGHTS One-dimensional Boussinesq equation after incorporating constant SI and ET was found appropriate to signify stream–aquifer interaction in the semi-infinite flow region.; Both recharging and discharging aquifers, water table profiles at 1 day and 5 days as obtained from FES followed by FIFDS were observed quite close to HFAS.; Performance of AS I was better than AS II in both recharging and discharging aquifers.;

This study presents a simple framework methodology for selecting the most appropriate locations for managed aquifer recharge (MAR). The proposed approach is applicable to aquifers that are located in coastal or mountainous areas and are used either for agricultural or industrial (e.g., mining) activities. A characteristic case study for the identification of the areas that are the most suitable for aquifer recharge using a GIS multi-criteria decision analysis (GIS-MCDA) method by means of MAR type spreading methods is the Geropotamos basin, Crete, Greece. Criteria combining a high relevance and high data availability, and providing unique information, were selected to assess the suitability of aquifer recharge in the basin. The criteria applied to evaluate the sites’ suitability for MAR spreading methods are hydrogeology, slope, land use, rainfall, groundwater level, soil texture and distance to source water. This study uses the ‘Pairwise comparison’ to assign criteria weights, as part of the Analytic Hierarchy Process (AHP), and examines four different scenarios. In all four scenarios, downstream areas, and close to the river Geropotamos, coincide as the most appropriate for aquifer recharge. HIGHLIGHTS aquifer recharge.; multi-criteria decision analysis (GIS-MCDA) method.; to identify suitable sites for implementing an MAR (Managed Aquifer Recharge) type spreading method.; This study uses the ‘Pairwise comparison’ to assign criteria weights.; Analytic Hierarchy Process (AHP).;

Though riparian areas generally have a shallow water table and higher soil moisture compared to upslope areas, climatic seasonality may trigger water repellency in tropical riparian forests, which, if persistent, could negatively affect essential ecosystem functions related to water resources protection such as reduced overland-flow, sediment transport, and nutrient filtration. The objective of this study was to answer the following: can tropical riparian forests develop water repellency? If so, does water repellency affect infiltration on a seasonal basis? For this, water repellency and infiltration were measured in a grid of 72 points during a dry and a wet month of a tropical riparian forest with a shallow water table in a region with highly marked climatic seasonality. Water repellency and infiltration were significantly different between the wet and dry months. Water repellency affected negatively infiltration in the dry month, its effect in the wet month was insignificant. As a result, a higher infiltration capacity was observed over the wet period. Previous research has claimed that the development and persistence of repellency in soils could promote other hydrological processes such as overland flow. The findings shown here demonstrate that such phenomenon does not persist longer than the dry season. [ABSTRACT FROM AUTHOR]

Agricultural irrigation practices have changed through time as technology has enabled more efficient conveyance and application. In some agricultural regions, irrigation can contribute to incidental aquifer recharge important for groundwater return flows to streams. The Henrys Fork Snake River, Idaho (United States) overlies a portion of the Eastern Snake Plain Aquifer, where irrigated agriculture has occurred for over a century. Using irrigator interviews, aerial and satellite imagery, and statistical streamflow analysis, we document the impact of farm-scale decisions on basin-scale hydrology. Motivated to improve economic efficiency, irrigators began converting from surface to center-pivot sprinkler irrigation in the 1950s, with rapid adoption of center-pivot sprinklers through 2000. Between 1978–2000 and 2001–2022, annual surface-water diversion decreased by 311 Mm3 (23%) and annual return flow to the river decreased by 299 Mm3 over the same period. Some reaches that gained water during 1978–2000 lost water to the aquifer during the later period. We use an interdisciplinary approach to demonstrate how individual farm-scale improvements in irrigation efficiency can cumulatively affect hydrology at the landscape scale and alter groundwater-surface water relationships. Return flows are an important part of basin hydrology in irrigated landscapes and we discuss how managed and incidental aquifer recharge can be implemented to recover return flows to rivers.

Greater NOIDA evolved from 1991 with 101 villages to 2020 with 293 villages. This is an ideal case of rural to urban transformation in the immediate past. This transformation led to a decrease in recharging natural surfaces and an increase in impermeable surfaces. Along with the reduction in recharge areas, an increase in population has necessitated more and more extraction of groundwater resulting in an imbalance of water extraction and recharge. The result is depletion of groundwater levels in this area. The area is part of the wide Indo-Gangetic alluvium with sand, silt and clay layers resting on quartzite’s of Delhi Super Group. Geomorphological map prepared using digital elevation models of the area shows older and younger alluvial plains and active flood plains of the river Hindan. Time series analysis of key land use land cover classes shows that recharge areas were reduced from 77 % to 30 % from 2005 to 2019 and impervious surfaces have increased from 19 % to 65 % for the same period. Aquifers of the area are both phreatic and semi-confined. The aquifer parameters estimated through step drawdown test and long duration aquifer performance test indicates that the average coefficient of transmissivity of the area is 1752 m2/day and the average coefficient of storage is 4.84 x 10-4. Discharge of the wells shows a yield of 8 to 16 lps for a drawdown of 3 to 6 m. An attempt has been made to know the behaviour of groundwater levels during the same period as that of land use land cover. The results indicate a 74 % depletion in groundwater levels with an average annual depletion of 21 %. An interrelationship between urban growth and groundwater levels has been established in this study. This analysis indicates that as agriculture declined water levels also depleted and have a positive correlation of 0.852. On the contrary, as the built-up increased water level has depleted hence have a negative relationship with a correlation coefficient of -0.851. To make it a sustainable resource, these overexploited aquifers need careful participatory management by communities, Scientists, and policymakers.

The pressure on Egypt's limited water resources has increased as a result of the country's growing industrial and agricultural sectors, coupled with climate change impacts and population growth. To overcome the current water stress situation, the utilization of new technologies such as managed aquifer recharge (MAR) is thought to be key for expanding the use of non-conventional water resources and providing necessary water supplies. Managed aquifer recharge can boost groundwater recharge and promote greater water accessibility. Suitability maps for MAR are widely offered as a tool to aid in decision-making in the context of balancing water demand and supply. Conducting a sensitivity analysis to validate suitability mapping can enhance the understanding of the results and pinpoint the influencing factors. The West Delta region was chosen as a case study given the existence of two MAR sites to examine the suitability of implementing MAR projects with reclaimed water. In this work, a spatially explicit sensitivity analysis is performed on a newly developed framework for MAR suitability maps that use multi-criteria decision analysis (MCDA) to determine suitable locations for MAR implementation, using spreading methods techniques. The performed sensitivity analysis uses spatial visualization to examine the effect of various weighted criteria on the final outputs and identifies criteria that are especially sensitive to weight changes. The results of the sensitivity analysis indicate that the applied MCDA framework for the suitability mapping in West Delta produced robust results in terms of the most suitable sites for MAR. The obtained results also indicate the possibility of the use of the suggested framework for arid environments with comparable data availability. Moreover, the results emphasize the possible use of suitability maps in sustainable groundwater management plans to support the actual implementation of MAR projects in the West Delta. [ABSTRACT FROM AUTHOR]

With increasing exploitation of groundwater resources and implementation of various activities in their recharge areas, it is vital to conduct a comprehensive assessment of aquifers to ensure their conservation and sustainable management. In the present study, we used a comprehensive approach to conceptualise and identify the functioning of two connected aquifer systems in north-eastern Slovenia: the Quaternary porous aquifers Dravsko polje and Ptujsko polje. The study presents the conceptual models of both aquifers and their interconnectedness using separate mathematical-numerical models with the aim of ensuring an integrated management of these alluvial aquifer systems. It also highlights the importance of understanding connections between such systems for simulating groundwater flow and transport of different contaminants. To describe the entire aquifer system, the study defines its three essential elements: the geometry of the aquifers, their recharge by precipitation, and other boundary conditions. The geometry of the Quaternary aquifers was defined using Sequential Indicator Simulation (SIS) with the ESRI's ArcMap software. Next, LIDAR was used for determining their surface geometry. The hydrogeologic model was designed using the Groundwater Modelling System (GMS) developed by AQUAVEO. We used the MODFLOW 2000 calculation method based on the finite difference method (FDM). The model was calibrated with the PEST module, which was used to calibrate hydraulic conductivity and hydraulic heads between the measured and modelled data. Finally, the model was validated using the Nash–Sutcliffe (NSE) efficiency coefficient. In addition, the model results estimated using the PEST tool were validated with the hydraulic conductivities determined at the pumping sites (pumping tests), each belonging to water protection zones that define the maximum travel time of the particles. This was performed using the MODPATH method. The paper also presents the possibility of modelling heterogeneous but interdependent aquifers in a groundwater body. Modelling the connection between the two aquifers, which are the most important ones in the region, is essential for a comprehensive management of the entire system of water resources. The models allow for a better understanding of groundwater flow in both aquifers. Moreover, their interconnectedness will be used for further studies in this field, as well as for integrated water management. [ABSTRACT FROM AUTHOR]

This study presents a simple framework methodology for selecting the most appropriate locations for managed aquifer recharge (MAR). The proposed approach is applicable to aquifers that are located in coastal or mountainous areas and are used either for agricultural or industrial (e.g., mining) activities. A characteristic case study for the identification of the areas that are the most suitable for aquifer recharge using a GIS multi-criteria decision analysis (GIS-MCDA) method by means of MAR type spreading methods is the Geropotamos basin, Crete, Greece. Criteria combining a high relevance and high data availability, and providing unique information, were selected to assess the suitability of aquifer recharge in the basin. The criteria applied to evaluate the sites' suitability for MAR spreading methods are hydrogeology, slope, land use, rainfall, groundwater level, soil texture and distance to source water. This study uses the 'Pairwise comparison' to assign criteria weights, as part of the Analytic Hierarchy Process (AHP), and examines four different scenarios. In all four scenarios, downstream areas, and close to the river Geropotamos, coincide as the most appropriate for aquifer recharge. [ABSTRACT FROM AUTHOR]

Groundwater recharge and discharge rates and zones are important hydrogeological characteristics of aquifer systems, yet their impact on the formation of both subterranean and surface microbiomes remains largely unknown. In this study, we used 16S rRNA gene sequencing to characterize and compare the microbial community of seven different aquifers, including the recharge and discharge areas of each system. The connectivity between subsurface and surface microbiomes was evaluated at each site, and the temporal succession of groundwater microbial communities was further assessed at one of the sites. Bacterial and archaeal community composition varied between the different sites, reflecting different geological characteristics, with communities from unconsolidated aquifers being distinct from those of consolidated aquifers. Our results also revealed very little to no contribution of surface recharge microbial communities to groundwater communities as well as little to no contribution of groundwater microbial communities to surface discharge communities. Temporal succession suggests seasonal shifts in composition for both bacterial and archaeal communities. This study demonstrates the highly diverse communities of prokaryotes living in aquifer systems, including zones of groundwater recharge and discharge, and highlights the need for further temporal studies with higher resolution to better understand the connectivity between surface and subsurface microbiomes. [ABSTRACT FROM AUTHOR]

• The impact of recycled water reuse on infiltration and soil structure was evaluated. • Cation ratio of soil structural stability (CROSS) and SAR models were evaluated. • CROSS predicted the impact of recycled water reuse on soil infiltration better than SAR. • CROSS predicted the impact of recycled water reuse on soil structure better than SAR. Soil sodicity, salinity, clay dispersion, and clay soil cracking are significant issues for modern agriculture, especially in arid and semi-arid regions of the world. Sodium adsorption ratio (SAR) has traditionally been used to estimate potential changes in infiltration rates or hydraulic conductivity when sodium cations dominate irrigation water quality. Recent research indicates that the cation ratio of soil structural stability (CROSS f and CROSS opt) provides better predictive capabilities for soil structure and threshold electrolyte concentration than SAR, especially when water used for irrigation or aquifer recharge contains both potassium and sodium cations. In this study, soil columns filled with clay loam were used to assess the impact of recycled water reuse on soil structure stability and saturated hydraulic conductivity. Ten treatments were prepared using chloride solutions of sodium, potassium, calcium, and/or magnesium to create a broad range of synthetic recycled water qualities with varying SAR, CROSSf, and CROSS opt values. After a pre-saturation process, the columns were maintained to have a constant 1 cm head of treatment solutions with a salinity of 1.5 dS/m. The results showed that CROSS f had a stronger correlation with saturated hydraulic conductivity and soil aggregate stability in comparison to CROSS opt and SAR. The R2 for saturated hydraulic conductivity and soil structure were 0.90 and 0.94 for CROSS f , 0.41 and 0.60 for CROSS opt , and 0.75 and 0.78 for SAR, respectively. Notably, the treatments that received solutions with 0-SAR values but contained potassium had significantly more dispersible clay throughout the entire soil column than the treatment that received calcium chloride solution. It was concluded that the CROSS f model could offer enhanced accuracy and insight into predicting the impact of recycled water reuse for irrigation on soil infiltration rate and soil aggregate stability. [ABSTRACT FROM AUTHOR]

Study region: Calabar, Cross River State, Nigeria Study focus: Urban groundwater is a strategic water resource in Africa that offers a buffer against climate variability. Increasing population, extensive pollution, and climate change threaten the contribution of urban groundwater in compensating increasing freshwater demand. Modern urban areas are often established on productive alluvial aquifers because of the proximity between shallow water bodies and historical settlements. Groundwater dynamics in urban aquifers are complex. Impervious surfaces impede water infiltration, and leakage from water infrastructure contributes to groundwater recharge. In this study, groundwater dynamics of an African metropolis are assessed, and insights into aquifer protection are provided through detailed hydrogeological analysis and numerical models. New hydrogeological insights for the region: The Calabar metropolis (area of 166 km2 and 570,000 inhabitants) is characterized by a tropical climate, with annual rainfall of over 3000 mm/y and large groundwater resources enabling supply for 69% of the population. A simplified three-dimensional hydrogeological model of the metropolis was proposed using USGS-MODFLOW to assess groundwater resources and recharge rates. Recharge decreased to 46% from water-rich rural areas to disadvantaged and highly urbanized communities. Aquifer recharge driven by huge rainfall dilutes the nitrogen content and pathogens, contributing to an acceptable drinking water quality during the prolonged wet season.

Groundwater is a vital water supply for local populations and ecosystems globally. With the continuous population growth, the anthropic pressure on groundwater is ever increasing, thus reducing the amount of available water resource. Yet, estimating the impact of anthropogenic activities on aquifer recharge is still a significant challenge for research, especially in basement aquifers. This study aims to improve the actual knowledge of deep drainage and deep aquifer recharge pathways and dynamics in the basement as affected by land use/land cover (LULC). The methodology used in this study accounted for hydraulic processes in soil layers within both unsaturated and saturated zones in an integrated approach. An experimental setup consisting of three (3) experimental plots, respectively under natural vegetation (NV), cropped millet (CM) and cropped groundnut (CG) on which deep drainage was monitored during the years 2020 and 2021. The results show significant differences between the LULC types after two years of implementation. Deep drainage is improved under CM and CG plots located in the central valley, as compared to the NV plot located in the ridge zone. Deep drainage is estimated at 8%, 24% and 25% of the annual rainfall, respectively for NV, CM and CG. The ratio between the recharge value obtained by the water table fluctuation (WTF) method and the deep drainage tends to 1 for the CM and CG plots, highlighting a rapid water transfer between unsaturated and saturated zones. The central valley, which seems to be a preferential recharge pathway, provides promising insights under specific conditions for the implementation of artificial recharge infrastructures. [ABSTRACT FROM AUTHOR]

Reliable estimates of soil moisture and other field observations (e.g., precipitation, irrigation) are critical to quantify the seasonal variability of surface water and groundwater relationships. This is especially important in pasture-based agroecosystems that rely on surface water diversions and precipitation inputs for agricultural production. The objectives of this study were to (1) quantify soil water balance components in irrigated and non-irrigated pasture fields in western Oregon, USA and (2) evaluate soil moisture and shallow aquifer recharge relationships in irrigated vs. non-irrigated pasture fields. Four monitoring stations in each field were used to measure soil water content in the upper 0.8 m profile and shallow groundwater levels. A soil water balance (SWB) approach was used to determine deep percolation based on field measurements of several other hydrology variables (e.g., irrigation and soil moisture). The water table fluctuation method (WTFM) was used to estimate shallow aquifer response to irrigation and precipitation inputs. Results from this study add to the understanding of seasonal water transport through the vadose zone and into the shallow aquifer in agroecological systems with fine-textured soils in the Pacific Northwest region of the United States. [ABSTRACT FROM AUTHOR]

Dhaka is one of the highly populated cities in the world. Increased urbanization and population growth in Dhaka are mostly dependent on groundwater, with 78% of the supply water coming from the Plio-Pleistocene Dupi Tila aquifer. This research was conducted with the objectives of identifying ion chemistry, hydrochemical processes and their relationship to groundwater quality and finding out the impact of over-exploitation on Dupi Tila aquifer. Three consecutive semi-confined aquifers have been delineated up to the explored depth: the Upper Dupi Tila aquifer (UDA), Middle Dupi Tila aquifer (MDA) and Lower Dupi Tila aquifer (LDA). Hydrogeochemical processes and water quality have been inferred from bivariate plots, correlation of major ions, piper plot and stable isotopes analysis. The total dissolved solids show an increasing downwards trend from an average of 267 mg/l in UDA to an average of 284 mg/l in LDA. Waters in all three aquifers as well as surface water (SW) are mainly of Ca/Mg-HCO3 type. The weathering of aluminosilicates controls the concentration of the major ions. Even though there is a significant decline in piezometric level both in UDA (> –85 m Public Works Department reference datum (PWD)) and MDA (> –65 m PWD), there is no evidence of groundwater recharge through direct infiltration from the river. The stable isotopes indicate most of the UDA, MDA and LDA waters are mainly from local precipitation. Increasingly enriched mean values for stable isotopes for the subsequent aquifers UDA, MDA and LDA, as well as increasing PCO2 for UDA < MDA < LDA, indicate increasingly warmer recharge conditions. The overall groundwater quality in the aquifers is good. At present, we have no indication that groundwater exploitation has altered groundwater quality of the Dupi Tila aquifer. Therefore, it is of vital importance to regularly monitor water quality for the purposes in order to timely detect any potential water quality alteration that could be aggravated by the vast decline in piezometric level, in view of the long-term sustainable development of the groundwater resources of this city. [ABSTRACT FROM AUTHOR]

Enhanced aquifer recharge (EAR) is defined as any engineered structure or enhanced natural feature designed to convey stormwater, surface water or wastewater directly into an aquifer (e.g. aquifer storage and recovery (ASR) wells) or into the vadose zone eventually percolating to an aquifer (e.g. spreading basins, dry well, etc.; USEPA 2021). Identifying the storage and flow capabilities of complex aquifers can improve the efficacy of many conceptual site models (CSM) for sites considered for ASR projects. In a karst setting, the EAR process may be able to take advantage of natural surficial features and the increased storage capacity of karst aquifers to improve recharge to groundwater. However, the suitability for an EAR project in a karst setting depends on the maturity of the karst and its preceding epikarst. The focus of flow within the epikarst causes enlargement of fractures and karst conduits. Thus, the storage and transmissivity within the karst vary greatly. Electrical resistivity imaging (ERI) is a well-known geophysical tool for mapping fractures and sinkholes, typical in karst settings. Locating enhanced water conveyance structures of a karst aquifer can improve the design and operation of an EAR site. This study investigated the hydraulic connection between shallow and deep groundwater using ERI to identify potential flow pathways and to improve our understanding of the storage mechanisms of the epikarst. The results presented in this paper validate the effectiveness of ERI in characterizing karst/epikarst and delineating soil, bedrock and local faults and fractures in the subsurface. [ABSTRACT FROM AUTHOR]

Nature-Based Solutions for Integrated Water Resources Management (NbS-IWRM) involve natural, or nature-mimicking, processes used to improve water availability in quantity and quality sustainably, reduce the risks of water-related disasters, enhance adaptation to climate change and increase both biodiversity and the social-ecological system's resilience. United Nations and the European Commission promote their research as a cornerstone in the changeover to the Ecological Transition. In the Sierra Nevada range (Spain) and the Andean Cordillera, there is a paradigmatic and ancestral example of NbS-IWRM known as "careo channels" and "amunas", respectively. They recharge slope aquifers in mountain areas and consist of an extensive network of channels that infiltrate the runoff water generated during the snow-thawing and rainy season into the upper parts of the slopes. The passage of water through the aquifers in the slope is used to regulate the water resources of the mountain areas and thus ensure the duration of water availability for the downstream local population and generate multiple ecosystem services. This form of water management is known as Water Sowing and Harvesting (WS&H). As shown in this work, it is a living example of a resilience and climate change adaptation tool that can be qualified as a nature-based solution. [ABSTRACT FROM AUTHOR]

Aquifer recharge is one of the most important hydrologic parameters for understanding available groundwater volumes and making sustainable the use of natural water by minimizing groundwater mining. In this framework, we reviewed and evaluated the efficacy of multiple methods to determine recharge in a flood basalt terrain that is restrictive to infiltration and percolation. In the South Fork of the Columbia River Plateau, recent research involving hydrologic tracers and groundwater modeling has revealed a snowmelt-dominated system. Here, recharge is occurring along the intersection of mountain-front alluvial systems and the extensive Miocene flood basalt layers that form a fractured basalt and interbedded sediment aquifer system. The most recent groundwater flow model of the basin was based on a large physio-chemical dataset acquired in laterally and vertically distinctive locations that refined the understanding of the intersection of the margin alluvium and the spatially variable basalt flows that filled the basin. Modelled effective recharge of 25 and 105 mm/year appears appropriate for the basin's plain and the mountain front, respectively. These values refine previous efforts on quantifying aquifer recharge based on Darcy's law, one-dimensional infiltration, zero-flux plane, chloride, storage, and mass-balance methods. Overall, the combination of isotopic hydrochemical data acquired in three dimensions and flow modelling efforts were needed to simultaneously determine groundwater dynamics, recharge pathways, and appropriate model parameter values in a primarily basalt terrain. This holistic approach to understanding recharge has assisted in conceptualizing the aquifer for resource managers that have struggled to understand aquifer dynamics and sustainable withdrawals. [ABSTRACT FROM AUTHOR]

The Kingdom of Saudi Arabia (KSA) is an arid country facing the challenge of renewable freshwater availability. KSA has an area of about 2.25 million km2. KSA has no perennial rivers or permanent freshwater bodies. KSA has low rainfalls with high evaporation rates which makes it very dry country. After discovering oil, KSA has witnessed remarkable economic development and rapid increase in population with migration to the urban areas in the past four decades. KSA population increased from about 4 million in 1960 to about 32.5 million in 2018. These developments lead to more pressure due to increased demand on the scarce freshwater resources. In order to meet the growing water demands, the limited renewable freshwater resources have been heavily overexploited. Groundwater aquifers are the main natural renewable freshwater source in the country. The average per capita municipal daily water use in KSA has been increasing since 2009 when it hit 227 L/d and recorded a gradual increase to touch 270 L/d in 2016 which is the 3rd highest in the world. Faced with increasing water scarcity and gaps between water supply and demand, policymakers in KSA started to consider the treated wastewater as a major renewable water source and aim to achieve full utilization and reuse of treated wastewater by 2025. With a desalination capacity of about 2,500 million cubic meters per year which represents 30% of the world's desalination capacity, KSA is the largest seawater desalination producing country. However, desalinated water alone will not be able to supply enough freshwater to meet the increasing future water demand. However, with only 10% of the total municipal wastewater generated currently being reused, KSA is projected as the third largest reuse market after China and the USA, and reuse capacities are projected to increase by 800% by 2025. The projected growth and change in water portfolios offer tremendous opportunities to integrate novel approaches of water reclamation and reuse such as aquifer recharge and groundwater quality enhancement, district cooling and irrigation of reactional areas. Recent statistics in 2018 indicated that the volume of treated wastewater used to produce freshwater in KSA was approximately 390 million cubic meters per year. This statistic shows the revenue of the industry "sewerage" in Saudi Arabia from 2012 to 2017, with a forecast to 2024. It is projected that the revenue of sewerage in Saudi Arabia will amount to approximately 739.3 million U.S. Dollars by 2024. The KSA's treated wastewater utilization status up to date and the main key challenges facing KSA such as the substantial growth in wastewater services demand; low coverage of existing wastewater collection systems, treatment facilities, and reuse options; and the needed governmental capital investment in wastewater infrastructure development were analyzed. It has been recommended that there are initiatives that should be taken thus far to tackle these challenges towards successful achievement of KSA's efficient wastewater treatment and reuse. [ABSTRACT FROM AUTHOR]

The Riardo basin hosts groundwater exploited for the production of high quality, naturally sparkling, bottled water (e.g., Ferrarelle water), and circulating in a system constituted by highly fractured Mesozoic carbonates, overlain by more impervious volcanic rocks of the Roccamonfina complex. The two formations are locally in hydraulic connection and dislocated by deep-rooted faults. The study aimed at elucidating groundwater origin and circulation, using isotopic tracers (δ18O, δ2H, δ11B and 87Sr/86Sr) coupled to groundwater dating (Tritium, CFCs and SF6). Besides recharge by local precipitation over the Riardo hydrogeological basin, stable isotope ratios in water indicated an extra-basin recharge, likely from the elevated surrounding carbonate reliefs (e.g., Maggiore and Matese Mts.). The mineralization process, promoted by the deep CO2 flux, controls the B and Sr contents. However, their isotopic ratios did not allow discriminating between circulation in the volcanic and in the carbonate aquifers, as in the latter the isotopic composition differed from the original marine signature. Groundwater model ages ranged from ~ 30 years for the volcanic endmember to > 70 years for the deep, mineralized end-member, with longer circuits recharged at higher elevations. Overall, the results of this study were particularly relevant for mineral water exploitation. A recharge from outside the hydrogeological basin could be evidenced, especially for the more mineralized and valuable groundwater, and an active recent recharge was detected for the whole Riardo system. Both findings will contribute to the refinement of the hydrogeological model and water budget, and to a sustainable development of the resource. [ABSTRACT FROM AUTHOR]

The Kara River watershed (KRW), northern Togo, is facing climate-change impacts that have never been clearly characterized. Six decades of rainfall data (1961–2020) from six measuring stations ideally distributed across the watershed were used in this study. The flow records from two stations situated in contrasting locations on the KRW were also used. Statistical tests were conducted to assess the spatial and temporal variability of the rainfall and to detect tendencies within these meteorological series. The water balance method and calculation of the dry-off coefficient and of the groundwater volume drained by rivers allowed evaluating the impact of climatic evolution on surface flow and on groundwater volumes during the six decades studied. The results showed contrasting spatiotemporal variability of rainfall (and of aquifer recharge) over the watershed with a decreasing tendency upstream and an increasing one downstream. At the same time, the water volume drained by the aquifer to sustain the river's base flow decreased from −22% to −36% depending on the measuring station. These results constitute a decision-making tool for Togolese water resource managers and are of primary importance for characterizing the fate of water resources worldwide in regions subject to severe droughts. [ABSTRACT FROM AUTHOR]

Literature provides only a few examples of contamination of groundwater with microplastics, mainly investigated using a chemical approach. Little importance is given to the hydrogeological processes able to affect the contamination, such as river–groundwater interactions. This study was carried out with two aims. The first aim is the formulation of a method with a high result-to-cost ratio, based on the hydrogeological aspects of the investigated area. Microplastics were extracted from samples through filtration and successively counted and characterized morphologically through analysis of optical microscopy images. The second aim is to evaluate the presence of microplastics in some portions of an alluvial aquifer using this methodology. Microplastics in groundwater showed a higher circularity and Feret diameter than those found in surface waters, indicating that in porous aquifers the transport is likely more influenced by the microplastics' shape than by their size. The aquifer recharge did not modify the microplastics' characteristics in groundwater, whereas in surface water the flood wave promoted the resuspension of microplastics with lower circularity. These findings provide new pieces of evidence on the presence and transport of microplastics in both groundwater and surface waters, underlining how the hydrogeological characteristics of the area can be one of the main drivers of microplastics' contamination. [ABSTRACT FROM AUTHOR]

Stigmatization of water and food products can constrain markets and prevent the implementation of scientifically safe solutions to environmental problems, such as water scarcity. Recycled water can be a cost‐effective, dependable, and safe solution to water shortages. However, consumers generally either require a large reduction in price to purchase products made with recycled water or reject such products outright. If emerging sustainable agricultural technologies, such as recycled water, are to be used to address growing water shortages worldwide, policymakers, water managers, and industry stakeholders must identify effective strategies for mitigating the stigma associated with recycled water. Using field experiments involving 1420 adult participants, we test the effectiveness of two stigma‐mitigating techniques. We also demonstrate a novel twist to the collection of representative samples in non‐hypothetical field experimental settings and then compare the results to a more traditional field experiment that recruited participants at large public gatherings. The analysis of these two different samples suggests a common finding: passing recycled water through a natural barrier, such as an aquifer, removes the stigma consumers would otherwise attach to it. We also find that the trophic level an organism occupies in the food chain influences stigmatizing behavior. The greater the steps in the food chain between an organism and the use of recycled water, the less it is stigmatized by consumers. These results have important implications for efforts to promote large‐scale potable and non‐potable water recycling projects and the use of recycled water in the agricultural industry. [ABSTRACT FROM AUTHOR]

The lack of valuable baseline information about groundwater availability hinders the robust decision-making process of water management in humid, arid, and semi-arid climate regions of the world. In sustainable groundwater management, identifying the spatiotemporal and extrapolative monitoring of potential zone is crucial. Thus, the present study focused on determining potential aquifer recharge zones using geospatial techniques for proxy data of the Gilgel Gibe catchment, Ethiopia. Proxy data are site information derived from satellite imageries or conventional sources that are operated as a layer attribute in the geographical information system (GIS) to identify groundwater occurrence. First, GIS and analytical hierarchy process (AHP) were applied to analyze ten groundwater recharge controlling factors: slope, lithology, topographic position index lineament density, rainfall, soil, elevation, land use/cover, topographic wetness index, and drainage density. Each layer was given relative rank priority depending on the predictive implication of groundwater potentiality. Next, the normalized weight of thematic layers was evaluated using a multi-criteria decision analysis AHP algorithm with a pairwise comparison matrix based on aquifer infiltration relative significance. Lithology, rainfall, and land use/cover were dominant factors covering a weight of 50%. The computed consistency ratio (CR = 0.092, less than 10%) and consistency index (CI = 0.1371) revealed the reliability of input proxy layers' in the analysis. Then, a GIS-based weighted overlay analysis was performed to delineate very high, high, moderate, low, and very low potential aquifer zones. The delineated map ensures very high (29%), high (25%), moderate (28%), low (13%), and very low (5%) of the total area. According to validation, most of the inventory wells are located in very high (57%), high (32), and moderate (12%) zones. The validation results realized that the method affords substantial results supportive of sustainable development and groundwater exploitation. Therefore, this study could be a vigorous input to enhance development programs to alleviate water scarcity in the study area. [ABSTRACT FROM AUTHOR]

Quantifying soil water budget components, and characterizing groundwater recharge from irrigation seepage, is important for effective water resources management. This is particularly true in agricultural fields overlying shallow aquifers, like those found in the Willamette Valley in western Oregon, USA. The objectives of this two-year study were to (1) determine deep percolation in an irrigated pasture field with clay soils, and (2) assess shallow aquifer recharge during the irrigation season. Soil water and groundwater levels were measured at four monitoring stations distributed across the experimental field. A water balance approach was used to quantify the portioning of different water budget components, including deep percolation. On average for the four monitoring stations, total irrigation applied was 249 mm in 2020 and 381 mm in 2021. Mean crop-evapotranspiration accounted for 18% of the total irrigation applied in 2020, and 26% in 2021. The fraction of deep percolation to irrigation was 28% in 2020 and 29% in 2021. The Water Table Fluctuation Method (WTFM) was used to calculate shallow aquifer recharge in response to deep percolation inputs. Mean aquifer recharge was 132 mm in 2020 and 290 mm in 2021. Antecedent soil water content was an important factor influencing deep percolation. Study results provided essential information to better understand the mechanisms of water transport through the vadose zone and into shallow aquifers in agricultural fields with fine-textured soils in the Pacific Northwest region in the USA. [ABSTRACT FROM AUTHOR]

Study region: The Lower Flint River Basin (LFRB): a karst catchment in southwestern Georgia, USA. Study focus: A year-long field campaign from July 2018 to July 2019 measured steady and dynamic stream-aquifer exchanges on Ichawaynochaway Creek (INC), a fifth-order tributary to the karstic Flint River in Georgia. The net change in discharge along a 24-km Creek segment was determined between two US Geological Survey gaging stations with no surface-water inflows. Stream-aquifer interactions were measured along a 120-m piezometer transect perpendicular to the bank. Hydraulic parameters to aid future modeling efforts were estimated using the method of moments applied to changes in bank flow direction from Hurricane Michael. New hydrological insights for the region: Results display the effects of local water use on streamflow as most channel storage gains occurred in the fall and winter. Negligible net channel gains and some losses occurred during the spring and summer months. Approximately 150 million m3 of net channel gains were observed during the study period. Initial stormflow contributed to aquifer recharge as indicated by reversals in the hydraulic gradient. Diffusivity and transmissivity increased along the transect (9–420 m2/d) and (3–150 m2/d), respectively, and hydraulic conductivity equaled 2.85 m/d. Stream-reach orientation with respect to regional groundwater gradients explains increased stream-aquifer interactions. Surface-groundwater interactions in karst systems are better understood after characterizing variation of hydraulic processes.

A reasonable estimation of aquifer recharge can assist in the sustainable management of groundwater resources. The methodology to calculate aquifer recharge presents many challenges due to geological complexity and the existence of different water qualities in the aquifer. The classic chloride mass balance (CMB) method has been used widely for aquifer recharge estimation but the assumptions in the equations neglect other sources of chloride than rainfall; chloride accumulation due to evaporation and the hydraulic properties of the recharged aquifer. This research aims to introduce modifications and derive a new CMB equation that covers the shortcomings in the earlier classic CMB approach. The newly developed approach was verified mathematically to identify the sensitive parameters that affect the results of aquifer recharge. Also, it was verified by independent data and method (groundwater modelling) and showed that it is approaching reality about recharge estimation than the earlier classic method which underestimates aquifer recharge especially for brackish aquifers. This article applies the new modified method to sedimentary aquifers of brackish nature and carbonate aquifers predominantly with fresh water and brackish water. In particular, numerical modelling showed that the optimum percentage of aquifer recharge from rainfall for brackish aquifers is between 10% and 20%. Application of the classic method in brackish aquifers in Kuwait estimates the aquifer recharge to be 0.5%–3% due to rainfall, while the modified method yields aquifer recharge of 9.3%–20% from total rainfall which agrees with the results of numerical modelling approach. The application of the classic CMB method for the carbonate aquifers containing fresh to brackish groundwater in the West Bank, gave recharge percentage of 25% from rainfall while the modified method indicated the recharge percentage is 32% from rainfall. The results of the study obtained by the modified CMB technique are proved promising. [ABSTRACT FROM AUTHOR]

An index to identify potential recharge zones (PRZs) in alluvial aquifers was developed to protect these zones during land use planning. The PRZ index was designed as an additive index through the selection of five characterization indicators. The variables were then operationalized and categorized to generate a conceptual model of the physicalgeological system. The PRZ index places recharge zones into four classes according to their potential. This index was applied to the Bolo River hydrogeological area (Valle del Cauca, Colombia), and the following proportions were identified for each PRZ category with a total area greater than 426 km²: very high: 23%, high: 30%; moderate: 40% and low: 7%. The areas with a very high recharge potential were found in the upper portion of the debris cones; their potential was predominantly due to the presence of sand and gravel unconfined aquifers and to aquifer outcrop layers at depths of less than 2.5 m. These PRZs were validated with piezometry, and the hydraulic gradient for 71% of the area was greater than 1%. These areas should be declared protected areas. [ABSTRACT FROM AUTHOR]

With increasing exploitation of groundwater resources and implementation of various activities in their recharge areas, it is vital to conduct a comprehensive assessment of aquifers to ensure their conservation and sustainable management. In the present study, we used a comprehensive approach to conceptualise and identify the functioning of two connected aquifer systems in north-eastern Slovenia: the Quaternary porous aquifers Dravsko polje and Ptujsko polje. The study presents the conceptual models of both aquifers and their interconnectedness using separate mathematical-numerical models with the aim of ensuring an integrated management of these alluvial aquifer systems. It also highlights the importance of understanding connections between such systems for simulating groundwater flow and transport of different contaminants. To describe the entire aquifer system, the study defines its three essential elements: the geometry of the aquifers, their recharge by precipitation, and other boundary conditions. The geometry of the Quaternary aquifers was defined using Sequential Indicator Simulation (SIS) with the ESRI’s ArcMap software. Next, LIDAR was used for determining their surface geometry. The hydrogeologic model was designed using the Groundwater Modelling System (GMS) developed by AQUAVEO. We used the MODFLOW 2000 calculation method based on the finite difference method (FDM). The model was calibrated with the PEST module, which was used to calibrate hydraulic conductivity and hydraulic heads between the measured and modelled data. Finally, the model was validated using the Nash–Sutcliffe (NSE) efficiency coefficient. In addition, the model results estimated using the PEST tool were validated with the hydraulic conductivities determined at the pumping sites (pumping tests), each belonging to water protection zones that define the maximum travel time of the particles. This was performed using the MODPATH method. The paper also presents the possibility of modelling heterogeneous but interdependent aquifers in a groundwater body. Modelling the connection between the two aquifers, which are the most important ones in the region, is essential for a comprehensive management of the entire system of water resources. The models allow for a better understanding of groundwater flow in both aquifers. Moreover, their interconnectedness will be used for further studies in this field, as well as for integrated water management.

The sources of groundwater salinization, as well as the recharge modes in the Essaouira coastal aquifer, were investigated using a multi-assessment approach that combines hydrogeochemical, multivariate statistical, and isotopic analyses along with geostatistical and remote sensing tools. The multivariate statistical assessment reveals three types of parameters inducing groundwater degradation in the studied aquifer: (1) natural parameters (Na, Cl, NO3, HCO3, Ca, SO4, K, and Mg), (2) the anthropogenic impact represented by NO3, and (3) the processes controlling HCO3 concentration in groundwater. The hydrogeochemical analyses denote the predominance of Ca-Mg-Cl and Na-Cl chemical facies and implicate a multitude of processes that induce groundwater mineralization in the Essaouira coastal aquifer. The stable isotope analyses identify recharge modes, and reveal a recharge dilution effect on groundwater quality close to the river. The interpretation of nitrate levels associated with different land uses suggests that domestic sewer leakage and livestock activities are the major sources of nitrate pollution in the studied aquifer. The adopted multi-assessment approach reveals the complexity and the interconnectivity between the different processes controlling groundwater quality in the Essaouira coastal aquifer. [ABSTRACT FROM AUTHOR]

Recharge of urban stormwater has often been limited by the high cost of land and concerns about contamination of groundwater. To provide a possible solution, we developed an electrochemical advanced oxidation system (UV/H2O2) that is compatible with high-capacity stormwater recharge systems (e.g., drywells). The system employed an air-diffusion cathode to generate a H2O2 stock solution (i.e., typically around 600 mM) prior to the storm event. The H2O2 stock solution was then metered into stormwater and converted into hydroxyl radical (•OH) by an ultraviolet lamp. The energy consumption for H2O2 generation was optimized by adjusting the applied current density and adding an inert salt (e.g., Na2SO4) to stormwater. H2O2 in the stock solution was unstable. By mixing the basic H2O2 containing catholyte and the acidic anolyte, the stability increased, enabling generation of the H2O2 stock solution up to three days prior the storm event with loss of less than 20% of the H2O2. Lab-scale experiments and a kinetic model were used to assess the feasibility of the full-scale advanced oxidation system. System performance decreased at elevated concentrations of dissolved organic carbon in stormwater, due to enhanced light reflection and backscattering at the water-air interface in the UV reactor, competition for UV light absorption with H2O2 and the tendency of organic matter to act as a •OH scavenger. The proposed system can be incorporated into drywells to remove greater than 90% of trace organic contaminants under typical operating conditions. The electrical energy per order of the system is estimated to range from 0.5 to 2 kWh/m3, depending on the dissolved organic carbon concentration.

The inland wetlands can perform the storage of water on the surface and the recharge of aquifers. Even a small wetland can work as a local point of water infiltration, influencing and sustaining the hydrodynamics in the hydrology landscape. These zones have complex mechanisms, as they integrate soil chemical and physical characteristics, and relate both surface and groundwater systems. The study area is an inland wetland located in the Ecological Station of Itirapina, São Paulo State (Brazil). The present work aims to unveil the relationship between hydrodynamics and pedological architecture through a detailed study that combines hydraulic conductivity tests in situ, geophysical method of electrical resistivity (Electrical Resistivity Tomography technique, ERT), and morphological soil descriptions aiming the validation of the ERT and hydraulic conductivity surveys. Two-dimensional (2D) and pseudo-three-dimensional (3D) ERT have been used to investigate the water flow in the subsurface, the pedological architecture that keeps the wetland hydroperiods, and the link between surface water and groundwater that can set a recharge capacity. The results showed areas with distinct surface patterns related to the density of vegetation cover and water infiltration. The lower infiltration areas are characterized by the presence of a perched water table in grassy areas while higher infiltration is associated with exposed topsoil. ERT 2D and pseudo-3D identified these areas as zones with a connection between soil-water and groundwater systems. Hydrodynamics in the flat plateau is associated with the geochemical evolution of soil cover due to the structural complexity acquired by the iron crust dissolution (laterite) which has sustained the relief. Future studies concerning inland wetlands need to be carried out to certify the role of soil-landscape in the water cycle in the Savanna biome.

Reliable estimates of soil moisture and other field observations (e.g., precipitation, irrigation) are critical to quantify the seasonal variability of surface water and groundwater relationships. This is especially important in pasture-based agroecosystems that rely on surface water diversions and precipitation inputs for agricultural production. The objectives of this study were to (1) quantify soil water balance components in irrigated and non-irrigated pasture fields in western Oregon, USA and (2) evaluate soil moisture and shallow aquifer recharge relationships in irrigated vs. non-irrigated pasture fields. Four monitoring stations in each field were used to measure soil water content in the upper 0.8 m profile and shallow groundwater levels. A soil water balance (SWB) approach was used to determine deep percolation based on field measurements of several other hydrology variables (e.g., irrigation and soil moisture). The water table fluctuation method (WTFM) was used to estimate shallow aquifer response to irrigation and precipitation inputs. Results from this study add to the understanding of seasonal water transport through the vadose zone and into the shallow aquifer in agroecological systems with fine-textured soils in the Pacific Northwest region of the United States.

Estimation of the infiltration/natural recharge to groundwater from rainfall is an important issue in hydrology, particularly in arid regions. This paper proposes the application of The Natural Resources Conservation Service (NRCS) mass balance model to develop infiltration (F)–rainfall (P) relationship from flash flood events. Moreover, the NRCS method is compared with the rational and the Ф‐index methods to investigate the discrepancies between these methods. The methods have been applied to five gauged basins and their 19 sub‐basins (representative basins with detailed measurements) in the southwestern part of Saudi Arabia with 161 storms recorded in 4 years. The F–P relationships developed in this study based on NRCS method are: F = 39% P with R2 = 0.932 for the initial abstraction factor, λ = 0.2. However, F = 77% P with R2 = 0.986 for λ = 0.01. The model at λ = 0.01 is the best to fit the data, therefore, it is recommended to use the formula at λ = 0.01. The results show that the NRCS model is appropriate for the estimation of the F–P relationships in arid regions when compared with the rational and the Ф index methods. The latter overestimates the infiltration because they do not take λ into account. There is no significant difference between F–P relationships at different time scales. This helps the prediction of infiltration rates for aquifer recharge at ungauged basins from monthly and annual rainfall data with a single formula. [ABSTRACT FROM AUTHOR]

The microbiome of an aquifer contaminated by landfill leachate and undergoing intrinsic remediation was characterised using 16S rRNA metabarcoding. The archaeal/bacterial V3–V4 hypervariable region of the 16S rRNA gene was sequenced using Illumina MiSeq, and multivariate statistics were applied to make inferences. Results indicate that the aquifer recharge and aquifer sediment samples harbour different microbial communities compared to the groundwater samples. While Proteobacteria dominated both the recharge and groundwater samples, Acidobacteria dominated the aquifer sediment. The most abundant genera detected from the contaminated aquifer were Polynucleobacter, Rhodoferax, Pedobacter, Brevundimonas, Pseudomonas, Undibacterium, Sulfurifustis, Janthinobacterium, Rhodanobacter, Methylobacter and Aquabacterium. The result also shows that the microbial communities of the groundwater varied spatially, seasonally and interannually, although the interannual variation was significant for only one of the wells. Variation partitioning analysis indicates that water chemistry and well distance are intercorrelated and they jointly accounted for most of the variation in microbial composition. This implies that the species composition and water chemistry characteristics have a similar spatial structuring, presumably caused by the landfill leachate plume. The study improves our understanding of the dynamics in subsurface microbial communities in space and time. [ABSTRACT FROM AUTHOR]

Study region: This study is along an intermittent reach of the Alamosa River in the San Luis Valley of south-central Colorado, a river that is typical of the semi-arid southwestern United States with respect to climate, land use, and the impacts of upstream dam regulation. Study focus: We use conceptual steady-state models to identify geologic factors that may control water loss through infiltration. These conceptual models are parameterized according to a range of conditions observed from stream discharge, topographic data, geologic data, and drone magnetometer data. New hydrological insights: The introduction of a fault, variation in the alluvial aquifer hydraulic conductivity, and presence or absence of a confining unit in the numerical models were the primary geologic controls that affected infiltration across the study reach. Conversely, variation in the thickness of the streambed had little impact. This information may help determine future data collection within this and similar semi-arid regions where rivers are controlled by a combination of surface water availability (e.g. through dam regulation) and complex subsurface geology, which are often not well constrained.

The water availability estimation in large regions is a relevant procedure to define broad water resources management policies but may prove difficult due to the lack of data and uncertainty to related regional hydrological and hydrogeological characterization. BALSEQ, a daily sequential water budget model, was applied in a set of twenty-two watersheds in southern Portugal, aiming to understand the possible relations between the model parameters and watershed characteristics that may allow assembling calibration functions for non-monitored watersheds. A sensitivity analysis was conducted by comparing BALSEQ results with measured surface flow, focusing specifically on the fraction of the potential maximum retention (φ) and the maximum amount of water available in the soil for evapotranspiration (AGUT) parameters and the underlying hydrogeological conceptual model that ultimately controls the surface-groundwater interactions. The overall results did not allow to identify clear relations that permit extrapolation to other regions without data as the sensitivity analysis procedures returned similar results for wide intervals of parameters for the majority of watersheds. The results confirmed that the groundwater discharge is an important component for the total measured surface flow and that the φ parameter should not be overlooked when calculating direct runoff. Poor adjustments between the model results and measured flow were observed in watersheds with a low Surface flow – Rainfall ratio.

Abstract This study assessed the relationship between the recharge of the unconfined sedimentary Adamantina Aquifer and its discharge into the Batalha River in a small basin of 125 km2 that drains the municipalities of Bauru, Agudos and Piratininga (SP, Brazil). According to the Eckhardt Flow Separation Filters and Soil Moisture Accounting Procedure methods, the recharge was 312.6 mm/yr and 232.0 mm/yr, respectively; and 286.2 mm/yr to the modified-Thornthwaite method for the 2000–2018 period. Recharge values prone to converge as more extended periods are analyzed (ideally 18 years) because the sensitivities to a specific parameter tend to be mitigated over time. With the integration of the methods, we established how changes in land-use impact the aquifer recharge and, thus, the discharges and the behavior of the river’s recession curve. Areas used to cultivate sugar cane (193 mm/yr), eucalyptus (150 mm/yr), or to urbanization (72 mm/yr) exert control over aquifer recharge even more than topography or type of soil. The combined and integrated use of three simple techniques allows them to be used for land-use planning and assessment of water availability in small hydrographic basins when hydrological data are scarce.

Quantifying soil water budget components, and characterizing groundwater recharge from irrigation seepage, is important for effective water resources management. This is particularly true in agricultural fields overlying shallow aquifers, like those found in the Willamette Valley in western Oregon, USA. The objectives of this two-year study were to (1) determine deep percolation in an irrigated pasture field with clay soils, and (2) assess shallow aquifer recharge during the irrigation season. Soil water and groundwater levels were measured at four monitoring stations distributed across the experimental field. A water balance approach was used to quantify the portioning of different water budget components, including deep percolation. On average for the four monitoring stations, total irrigation applied was 249 mm in 2020 and 381 mm in 2021. Mean crop-evapotranspiration accounted for 18% of the total irrigation applied in 2020, and 26% in 2021. The fraction of deep percolation to irrigation was 28% in 2020 and 29% in 2021. The Water Table Fluctuation Method (WTFM) was used to calculate shallow aquifer recharge in response to deep percolation inputs. Mean aquifer recharge was 132 mm in 2020 and 290 mm in 2021. Antecedent soil water content was an important factor influencing deep percolation. Study results provided essential information to better understand the mechanisms of water transport through the vadose zone and into shallow aquifers in agricultural fields with fine-textured soils in the Pacific Northwest region in the USA.

The quantification of the groundwater recharges represents useful and important information for water resource management. The volumes of infiltrated water are essential to maintain water storage in aquifers, as well as to the discharge of groundwater towards the rivers, especially in tropical areas. The outcrop zones of the Guarani Aquifer System (GAS) in São Paulo state (Brazil) are considered as their most important recharge areas; therefore, knowledge about recharge rates and processes is essential. They are also highly vulnerable to groundwater contamination, another important reason to protect them. This study aimed to estimate spatial and temporal variations of groundwater recharge in the mentioned GAS outcrop zones. Recharge rates were estimated using the Spatial Recharge (SR) method and then compared to other two traditional methods (base flow separation and water table fluctuation method). The SR method uses the spatial distribution of the evapotranspiration and rainfall from GLDAS and TRMM databases and the runoff after the Soil Conservation Service (SCS) empirical method. All three methods revealed similar estimates for groundwater recharge, ranging from 150 to 370 mm year−1 (about 17% of the total rainfall). Despite its intrinsic limitations, the SR method allowed robust recharge estimation with ability to cope with spatial and temporal variations, as well, especially in areas lacking hydrological monitoring programs. The SR method provides valuable information for water management policymakers and stakeholders to minimize impacts related to climatic variations and inappropriate land use on recharge processes. [ABSTRACT FROM AUTHOR]