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This study explores the causes of the acidic nature of the metal-rich, dilute groundwaters in the highland area of Ho Chi Minh City (HCMC), which is populated and mostly used for domestic, agricultural, and industrial purposes. The groundwater is generally very dilute (176 ± 128 µS/cm in electrical conductivity, 70 ± 220 µeq/L in alkalinity), but high in redox potential (343 ± 55 mV), and nitrate concentrations (19 ± 19 mg/L). Since the area corresponds to the highland and, thus, serves as a groundwater recharge zone. However, 53% and 90% of the investigated groundwater samples (n = 58) showed pH lower than 4 and 5, respectively, and, thus, 43%, 21%, and 7% of groundwater samples showed Al, Pb, and Cr concentrations exceeding their respective drinking water standards recommended by World Health Organization. Although nitrification is the most common acidification driver in the agricultural and/or urbanized lands, the nitrate concentration in this study area is strangely low compared to similar acidic groundwaters reported from other agricultural regions. To find out the causes of acidification, this study investigated the geochemical processes from the extensive groundwater chemistry data and performed geochemical simulations by changing water alkalinity and cation exchange capacity (CEC) of sediment and matching the results with the observed water chemistry data to confirm our hypothesis. Based on this approach, we could reveal that groundwaters of this study could become very acidic due to its dilute nature and low sediment CEC. Since groundwaters are generally very dilute in the recharge area, our finding provides another reason for the discreet management of highland areas where groundwater recharge is concentrated.

In Arusha urban, northern Tanzania, groundwater contributes about 80% of the water supply. However, elevated fluoride levels and evidence of anthropogenic pollution have been reported in the groundwater around Mount Meru which is a water source for Arusha urban. This study aims at understanding the recharge areas and flow pathways of groundwater in what has been a poorly monitored area. The study uses the isotopic ratio of oxygen and hydrogen to estimate the groundwater recharge area and flow pathway. The results show the recharge elevation of groundwater is between 1,800 and 3,500 m above mean sea level on the slopes of Mount Meru. The average fluoride contents in the study area are 5.3 ± 0.4 mg/L greater than the limits of 1.5 mg/L set by the World Health Organization (WHO) and Tanzania. The nitrate concentration of 83.9 mg/L at the lower elevation areas (

Water resources management is one of the most important challenges worldwide because water represents a vital resource for sustaining life and the environment. With the aim of sustainable groundwater management, the identification of aquifer recharge areas is a useful tool for water resources protection. In a well-developed karst aquifer, environmental isotopes provide support for identifying aquifer recharge areas, residence time and interconnections between aquifer systems. This study deals with the use of environmental isotopes to identify the main recharge area of a karst aquifer in the Upper Valley of Aniene River (Central Italy). The analysis of 18O/16O and 2H/H values and their spatial distribution make it possible to trace back groundwater recharge areas based on average isotope elevations. The Inverse Hydrogeological Balance Method was used to validate spring recharge elevations obtained by the use of stable isotopes. Areas impacted by direct and rapid rainfall recharge into the study area were delineated, showing groundwater flowpaths from the boundaries to the core of the aquifer. The results of this study demonstrate the contribution that spatial and temporal isotope changes can provide to the identification of groundwater flowpaths in a karst basin, taking into account the hydrogeological setting.

The Krawak Springs is a source of springs from the cracks of river rocks in the middle of a teak forest in Guwoterus Village, Montong District, Tuban. This spring is a source of irrigation water for agricultural land in the District of Montong. Based on its urgency, it is necessary maintaining its sustainability by identifying recharge areas and underground river flows. VLF is quite advantageous for use in the regional mapping underground rivers in karst areas because can describe the structure of the karst environment and predict interconnected pathways in karst. Data acquisition uses four tracks with an average length of about 300 m. Data processing was made qualitatively using MATLAB software and quantitatively using Inv2DVLF software. Qualitative results show that the conductive zone is identified as a subsurface river flow. From the processing results, it is known that the subsurface river flow zone can be identified as a zone that is conductive or has low resistivity. The underground river flow is interpreted to be located on Track 3 and Track 4 and has a direction of continuity to the southwest

Springs are a vital source of water supply in Quaternary volcanic environments, such as Rinjani Volcano on Lombok Island, and yet little is known about their emergence and recharge areas. Knowledge of spring recharge area can substantially support further spring analysis and management. This study was performed in two spring zones on the southern flank of Rinjani Volcano. It combined the available morphological, lithological, and hydrological datasets to build a conceptual model of the spring recharge areas. According to the analysis results, the conceptual model allowed to describe the flow medium, the aquifer type, and the characteristics of the flow system. The local morphology controlled the direction and gradient of groundwater flow to the springs. The analysis also revealed that the spring water in the study area was meteoric water, which mainly came from rainwater infiltration. Therefore, the boundaries of the spring recharge areas were represented by the morphological divides.

The eastern slope of Sumbing Vulcano, Central Java, Indonesia has many springs that causes most people use springs as a source of raw water. This area is part of the Magelang Temanggung Groundwater Basin which abundant groundwater potential. However water demand will continue to increase along with population growth. Therefore, conservative efforts to protect the recharge area are important. This study aims to determine the characteristics of groundwater recharge area on the eastern slope of Sumbing Vulcano using the isotope method. The research method was carried out by taking rainfall samples at 6 different elevations to obtain the meteoric water line (MWL) and the groundwater samples were taken from 11 stations consist of 10 springs and one deep well. The result shown that the recharge area was coming from local recharge with elevation around 273 masl to 1.208 masl.

The Raimanuk area in Timor, East Nusa Tenggara, is located in the Aroki Groundwater Basin. The decreasing quality and potential groundwater availability in the Aroki Groundwater Basin is feared due to its widespread use for household needs and agriculture. The lack of the groundwater recharge area map will pose an obstacle in policymaking regarding the management and preparation of spatial conservation areas in the Raimanuk Region. This study aims to determine the zone and classification of groundwater recharge areas in the Raimanuk area based on spatial data analysis. The groundwater recharge area can be determined using slope, river flow patterns, spring emergence, and groundwater table depth. The classification of the recharge area uses a scoring approach with an overlapping analysis of the parameter assessments, which are hydraulic conductivity, precipitation, soil cover, slope, and depth of unconfined groundwater. The result of the study is the groundwater recharge area map of Raimanuk. The groundwater recharge area is located in the Mandeu Hill area, which is the main recharge area. The groundwater discharge area is located in the Aroki plain area that can be the main recharge area.

High recharge areas significantly influence the groundwater quality and quantity in regional groundwater systems. Many studies have applied recharge potential analysis (RPA) to estimate groundwater recharge potential (GRP) and have delineated high recharge areas based on the estimated GRP. However, most of these studies define the RPA parameters with supposition, and this represents a major source of uncertainty for applying RPA. To objectively define the RPA parameter values without supposition, this study proposes a systematic method based on the theory of parameter identification. A surrogate variable, namely the average storage variation (ASV) index, is developed to calibrate the RPA parameters, because of the lack of direct GRP observations. The study results show that the correlations between the ASV indexes and computed GRP values improved from 0.67 before calibration to 0.85 after calibration, thus indicating that the calibrated RPA parameters represent the recharge characteristics of the study area well; these data also highlight how defining the RPA parameters with ASV indexes can help to improve the accuracy. The calibrated RPA parameters were used to estimate the GRP distribution of the study area, and the GRP values were graded into five levels. High and excellent level areas are defined as high recharge areas, which composed 7.92% of the study area. Overall, this study demonstrates that the developed approach can objectively define the RPA parameters and high recharge areas of the Choushui River alluvial fan, and the results should serve as valuable references for the Taiwanese government in their efforts to conserve the groundwater quality and quantity of the study area.

This research is being conducted on Upper Cisadane Watershed, Bogor, West Java Province. The aim of this research is to investigate the recharge area and analyze the recharge potential. The data consisted of infiltration rate, slope, soil type, and existing landuse as land unit approach which is collected by purposive sampling. Beside that, climate data were collected to estimate the evaporation. The analysis of the data use SCS-CN method to assess the volume of surface runoff, Penman-Monteith method to asseess the evaporation, and Water Balance Method to asseess the groundwater as the recharge potention. The recharge area would be classified into several areas into the highest to the lowest recharging area. The result of this study would be the total of groundwater fluxas the recharge potential based on each classified recharge area. The condition ofrecharge area could be one of the reasoning in develeoping the urban water system. The land with the good condition has surplus as ΔS=490,26 mm, and the critical one has deficit as ΔS=(-)543,49. The condition of the highest recharghing area would be analysed as the criteria of potential recharging area and the area should be managed well in the future. The condition of the lowest recharghing area would be restored depend on its problem.

Large, confined aquifer systems play a vital role in sustaining human settlements and industries in many regions. Understanding the sustainability of these water resources requires the evaluation of groundwater storage change. Direct in‐situ observation of groundwater storage is limited by the distribution and availability of groundwater level and aquifer storativity data. Here, we use and compare two auxiliary methods, applied at basin and sub‐basin scales, to assess groundwater storage changes in the Great Artesian Basin (GAB), one of the World's largest confined aquifer systems. The first, the groundwater budget, derives storage change as the residual of fluxes in and out of the GAB, assuming they are all accounted for and accurately estimated. The second uses time‐variable gravity data from GRACE satellites to estimate temporal changes in groundwater mass, assuming that all other components of the terrestrial water mass change detected by GRACE are correctly subtracted. Despite the depletion observed during the 20th century, groundwater storage is mostly stable during 2002–2022. An increase in storage is detected in the Surat sub‐basin, a major recharge area. This increase is attributed to an over‐representation of large recharge events during the study period and/or storage recovery following rehabilitation of free‐flowing bores. The approach consisting in disaggregating GRACE data assumes that water storage changes in confined aquifers is dominated by changes in the GAB, and as such, it may overestimate the increase in the GAB by incorrectly attributing the increase occurring in overlying aquifers to the GAB. In contrast, the recharge estimates used in the groundwater budgets do not account for flood recharge and might underestimate storage increase in the GAB. Plain Language Summary Monitoring groundwater storage in large, confined aquifers is often impossible as it requires large groundwater level and lithological data sets that are often unavailable. However, monitoring is crucial for assessing and managing the sustainability of this resource and manage it appropriately. This study uses and compares two auxiliary methods, applied at basin and sub‐basin scales, to assess groundwater storage changes in the Great Artesian Basin (GAB), one of the World's largest confined aquifer systems. The groundwater budget approach estimates water storage changes by adding up the amounts of groundwater that goes in and out of the aquifer system. The satellite gravimetry approach uses the temporal changes of Earth's gravity field to infer changes in groundwater mass. Both methods agree that, despite the depletion observed during the 20th century, groundwater storage in the GAB was mostly stable during 2002–2022. An increase in groundwater storage is detected near major recharge areas. It is attributed to an over‐representation of large recharge events during the study period and/or groundwater storage recovery following capping of free‐flowing bores. Key Points GRACE and groundwater budgets agree that water storage in the Great Artesian Basin was stable for the period 2002–2022 Increased storage in the Surat sub‐basin is attributed to bore rehabilitation and/or increased recharge during the study period Within the Surat sub‐basin, increased storage may be overestimated by GRACE and/or underestimated by the groundwater budgets