Identifying spring recharge areas using stable isotope and geophysical methods: A case study of the Ababi Mountain Region, Bali, Indonesia

Identifying spring recharge areas using stable isotope and geophysical methods: A case study of the Ababi Mountain Region, Bali, Indonesia | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Identifying spring recharge areas using stable isotope and geophysical methods: A case study of the Ababi Mountain Region, Bali, Indonesia I N. Simpen, I W. Redana, Putu D.H. Ardana, Anak A.N. Gunawan This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4279145/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Identifying spring recharge areas is essential for water resource conservation. This study aimed to determine the recharge area of Ababi Spring, Indonesia, using stable isotope, vertical electrical sounding (VES), and audio magnetotelluric (AMT) methods. Rainwater and spring water were sampled at 211–978 m locations above sea level. Hydrogen and oxygen isotope ratios revealed that spring water originated from a higher elevation source. The relationship between oxygen isotope composition and elevation was used to estimate the spring recharge elevation as 2,118-2,137 m above sea level. VES and AMT methods generated geoelectrical profiles depicting subsurface water flow from recharge to discharge zones, confirming the elevated recharge area. Additional isotope analysis of 1,514 m altitude rainwater supported the prediction model. This multidisciplinary approach combines hydrochemical and geophysical techniques to enable more reliable delineation of groundwater recharge areas than single methods. Determining the Ababi Spring recharge zone facilitates targeted conservation efforts for this vital water resource. Further work should investigate geochemical evolution along subsurface flow paths. Spring Recharge area Isotopes Vertical electrical sounding Audio magneto telluric Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 1. Introduction The depletion of water supplies is one of the most significant environmental issues of the twenty-first century (Ngene et al., 2021 ). One natural resource that is essential to human development and survival is water. It's getting harder and harder to find natural resources, particularly water (Yamashita & Ii, 2016 ). Every day, the amount of water used increases in tandem with the rate of population expansion. The preservation of groundwater resources, especially springs, depends on the position of recharge regions. The stable isotope approach can be used to define locations that receive spring recharge and groundwater. Several Indonesian regions—Bali in particular—have used the isotopic technique to determine groundwater genesis (Maria et al., 2021 ; Nuha et al., 2020 ; Toulier et al., 2019 ), particularly in Bali. The application of isotope 18O and 2H methods in Denpasar City to delineate the groundwater recharge zone in urban areas (Ardana et al., 2022 ). It also entails figuring out where springs recharge, which is the main supply of untreated mineral water in the Mambal region (Hendrayana et al., 2019 ). Oxygen and hydrogen form water, and both elements have isotopes. Conservatism makes 18 O and 2 H natural tracers (Pu et al. 2013 ; Sánchez-Murillo et al. 2015 ). Low-temperature water-rock interactions do not influence them (Marfia et al., 2004 ). Unaffected by harsh weather, rainwater from the top of the mountain or upstream region percolates through the soil until it reaches the land surface downstream. Wijatna et al. ( 2013 ) state that groundwater downstream (in wells or springs) will have oxygen and hydrogen isotope values similar to upstream precipitation. Because of this, the oxygen and hydrogen isotope levels of wells or springs from higher-elevation water recharge sites are lower than those from local rainfall. Therefore, local rainwater springs can be distinguished from higher-elevation catchment springs by their quantities of oxygen and hydrogen isotopes. This occurrence has motivated the use of natural isotopes as tracers to investigate the water dynamics of the hydrological cycle. To detect recharge and flow zones, isotopes are combined with groundwater from different sources and used as tracers in groundwater research (Blasch & Bryson, 2007 ; Mukherjee et al., 2007 ; Singh et al., 2013 ; Setiawan & Asgaf, 2016 ). Previous hydrogeological studies of the Ababi Spring system are limited. Toulier et al. ( 2019 ) applied isotope techniques to study the recharge processes of springs connected to Indonesia's Bromo-Tengger volcanic aquifer system but did not specifically focus on the Ababi Spring. Maria et al. ( 2021 ) also used hydrochemistry and environmental isotopes to delineate groundwater recharge areas in the South Bandung volcanic region but did not consider geophysical approaches. To date, no studies have combined stable isotope analysis with geoelectrical methods to map the recharge area of Ababi Spring. Several knowledge gaps remain regarding the origin and subsurface flow pathways of water discharging from this vital spring. This study addresses these gaps using an integrated approach coupling isotope hydrology and geophysics to delineate the recharge area effectively. The findings will aid water conservation efforts for the spring. Hydrogeological studies have revealed rocks and structural links up to a depth of 300 m (Agyemang, 2022 ). Ailes & Rodriguez ( 2014 ) identified aquifers in the San Luis Basin in New Mexico using the magnetotelluric methodology, and Bai et al. ( 2019 ) found overloaded structures and aquifers using the same method. To the best of our knowledge, it is challenging, costly, and impracticable to determine the recharge area of springs or groundwater using geochemical or geophysical approaches. This work combines the isotope technique, vertical electrical resistivity (VES) method, and magnetotelluric (audio magnetotelluric) method to measure the recharge area of the spring, thereby resolving the shortcomings of the previously mentioned methodologies. In the hilly Ababi Area, Abang District, Karangasem, spring catchment zones were identified using this methodology. This reservoir is the main water supply for the urban drinking water delivery system (PDAM) in the Karangasem District. The Ababi Spring's catchment area can be understood in order to carry out effective and efficient spring recharge area conservation efforts, ensuring the springs' continued existence. Determining groundwater recharge areas from traditional hydrogeological data alone poses significant challenges (Zamrsky et al., 2024 ). While isotope techniques can trace water sources (Zhou et al., 2023 ), they do not delineate subsurface flow paths. Conversely, geophysical surveys map subsurface structures but cannot independently identify hydrologic connections (Chen et al., 2023 ). This study utilizes a novel combination of stable isotope analysis, vertical electrical sounding (VES), and audio magnetotelluric (AMT) surveys to provide independent yet mutually consistent lines of evidence for mapping the recharge provenance and subsurface flow regime of the Ababi Spring. The convergence of geochemistry and geophysics facilitates more reliable groundwater basin characterization (Aguedai et al., 2022 ), especially in complex volcanic terrains. To date, this specific integrated approach has not been applied to delineate the Ababi Spring’s recharge area, representing an essential knowledge advancement. Therefore, this study aims to determine the recharge area and origin of the Ababi Spring using isotope techniques and validate flow connections to the identified recharge zone using geoelectrical surveys. The overarching goal is delineating the spring catchment to support long-term sustainable management. The technical approach integrates stable 2H and 18O isotope analysis, VES, and AMT methods. Isotope hydrology traces input water sources, while geophysics maps geological structures and hydrostratigraphy (Palano, 2022 ). This study represents the first application combining these specific techniques to effectively and reliably characterize the Ababi Spring recharge system. 2. Methodology The research employed various techniques, including data collection, calculations, analysis, and verification. Hydrogeological conditions, isotope ratio computations, and geoelectric and magnetotelluric interpretations were used to validate spring catchment regions. The study commenced with a literature review, the gathering of secondary data, and a field study to locate springs and other water sources. Indonesia’s Ministry of Energy and Mineral Resources published groundwater basin, hydrogeological, and geological maps, which were used in the study. 2.1 Study Sites Ababi Village is located in Abang District, Karangasem Regency, Bali Province, and boasts a spring at 8° 24' 8.14" S and 115° 35' 12.85" E (Fig. 1 ). Lake Batur extends further northwest, while Mount Agung is located northwest of the Ababi Spring. Ababi Village, spanning 10.86 km² and with an average elevation of 573 m above sea level (ASL), is a distinct and lovely place. Generally speaking, the village area is situated at the base of Mount Agung, with a Southeast-facing land slope. The tallest region is in the north, while modest hills, primarily rice fields, may be found in the east and center. There are plains to the west and south. The range of daytime temperatures was 29 to 35°C. 2.2 Hydrogeological environment The Amlapura groundwater basin includes Ababi Village (Mudiana & Setiadi, 2008 ). The Amlapura groundwater basin occupies an area of roughly 213.6 km2 and is situated in the Karangasem Regency in the eastern portion of Bali Province. With an average annual rainfall of 1,000 to 3,500 mm, it has a shallow groundwater potential of around 60 million m3/year and a profound groundwater potential of about 2 million m3/year. The basin's radial river flow pattern originates at the volcanic cone and expands outward in all directions, creating plains, rolling hills, and volcanic cones as morphological units. The basin's topographic elevation ranges from 0 to 3,500 m above sea level (Dinas Pekerjaan Umum Provinsi Bali, 2014 ). The main lithology of this basin, as shown in Fig. 3 , is alluvium deposits found in rivers and on beaches, which serve as an aquifer, which are primarily made up of medium-gradient sand and gravel; Agung volcanic rocks (Qhva), which are primarily made up of medium-gradient agglomerates, tuffs, lavas, and lahar deposits; and Seraya volcano rocks (Qvps), which are made up of low-gradient volcanic breccia and lava. (Purbo-Hadiwidjojo et al., 1998 ). A spring with a 5 l/s discharge rate is present (Sudadi et al., 1986 ). 2.3 Stable Isotopes Sun-evaporated seawater initiates hydrological cycles by becoming airborne through evaporation, with the wind subsequently carrying it to various locations such as the land, aquifers, rivers, lakes, and back to the sea. As the altitude decreases, the air pressure decreases, with mountains having a lower air pressure than the coast. Water-laden air rises or falls under atmospheric pressure, which affects the movement of water in the hydrological cycle. Height decreases the water-laden air temperature (lapse rate). Hydrogeologists use water-forming isotopes such as hydrogen ( 1 H, 2 H, and 3 H) and oxygen ( 16 O, 17 O, and 18 O) (Mazor, 2004 ; Goldscheider & Drew, 2007 ). The evaporated water had the following hydrogen and oxygen isotopes: 1H 99.985%, 2 H 0.015%, and 3 H less than 0.001%; 16 O 99.63%, 17 O 0.0375%, and 18 O 0.1995%. 16 O and 2 H precipitation decrease by 0.15–0.5 and 1–4 per 100 m in elevation, respectively (Clark, 2015 ). The D/1H and 18O/16O isotope ratios in water measured very low relative abundances (R) of 18 O and 2 H (or deuterium = D). R Std , SMOW, or seawater's D/1H or 18O/16O isotope ratios were compared. The ocean has the most significant evaporation process in the hydrological cycle; therefore, seawater has been used internationally as a reference. Most water samples (excluding seawater) had negative D and 18O isotopes. Figure 4 shows the hydrological cycle D and 18 O isotope fractionation (Pang et al., 2017 ; Kresic & Stevanovic, 2010 ; Mazor, 2004 ). In units of ‰ (per mil), the notations (δD)SMOW and (δ 18 O)SMOW are denoted as (δD) and (δ 18 O), respectively. δ smpl was used to express the sample isotopes' relative abundance (Nuha et al., 2020 ): \({\text{δ}}_{\text{sample}}\text{= }\frac{{\text{R}}_{\text{sample}}\text{-}{\text{R}}_{\text{std}}\text{ }}{{\text{R}}_{\text{std}}}\text{ x 100\%}\) (1) The relative abundances of the samples were the 18 O/ 16 O and 2 H/ 1 H isotope ratios, where R Std is the SMOW standard ratio. The 18 O and 2 H concentrations of the hydrological cycle vary due to these water isotopes' freezing points and vapor pressures. Evaporation, condensation, freezing, thawing, chemical reactions, and biological processes can cause isotope fractionation (Pang et al. 2017 ). Unless altered by magma, mixing, or evaporation, groundwater's 18 O and 2 H concentrations lie along the local meteoric line (rainwater). The straight line for rainwater differs from the 18 O and 2 H graphs. Elevation and precipitation frequencies affected the D/ 18 O isotope ratios. (D) and ( 18 O) increase with decreasing frequency and precipitation. Rain and precipitation frequency affect (D) and ( 18 O) at each sampling site; hence, equations 2 and 3 must be used to calculate the average value (Kresic & Stevanovic, 2010 ; Clark, 2015 ): \({\text{δ}}^{\text{18}}\text{O= }\frac{\sum _{\text{i=1}}^{\text{n}}{\text{P}}_{\text{i}}{\text{δ}}_{\text{i}}\text{18}\text{O}}{\sum _{\text{i=1}}^{\text{n}}{\text{P}}_{\text{i}}}\) (2) \({\text{δ}}^{\text{2}}\text{H= }\frac{\sum _{\text{i=1}}^{\text{n}}{\text{P}}_{\text{i}}{\text{δ}}_{\text{i}}\text{2}\text{H}}{\sum _{\text{i=1}}^{\text{n}}{\text{P}}_{\text{i}}}\) (3) where the following are included in the data set: Pi is the rainfall quantity between samples (i-1) and (i) (mm per month), δ i 18 O is the isotopic ratio of 18 O to SMOW in rainfall to (i) (‰), and δ i 2 H is the isotopic ratio of 2 H close to SMOW in rainwater to (i) (‰). 2.4 Electricity Sounding Vertically (VES) The VES measures the electrical resistance. Surveys measuring electrical resistivity provide direct current between the electrodes while evaluating the potential between them. The current penetration matched the electrode distance. Resistance stratification is visible in the electrode spacing (Hamzah et al., 2007 ). The Naniura NRD-300 HF was used for the VES survey, along with a laptop, electrodes, a machine, a cable, a connector, and a clamp (Fig. 5 ). Four straight-lined electrodes were spaced differently. Four electrodes require 200 m of wire, while 2 m are required. The two outer electrodes are currents, and the two inside electrodes have potential in a Schlumberger array (Koefoed). The spacing of the current electrode was 2–200 m (AB/2 = 1–100 m). 0.5–10 m separated potential electrodes (MN). Changes in the electrode spacing between measurements were collected from field data (Hamzah et al., 2007 ). According to Suryadi et al. ( 2018 ), the resistivity value can be differentiated or partitioned using the master curve developed by Schlumberger. Plotting the apparent resistivity on a graph log was the first step, after which the shape of the plotted apparent resistivity was compared or approximated by looking for a curve. The master curve can be used to calculate the resistivity and thickness partition. 2.5 Audio Magnetotelluric (AMT) An audio magnetotelluric (AMT) passive geophysical investigation utilizes high-frequency electromagnetic pulses ranging from 000 to 5 Hz to explore shallow to intense subsurface electrical conductivity. The AMT method determines subsurface electrical conductivity by measuring electromagnetic waves produced by the earth (Chave & Jones, 2012 ; Simpson & Bahr, 2005). The subsurface electrical conductivity of Earth is estimated via the electromagnetic passive-source inductive audio magnetotelluric model. Subsurface conductivity was measured using transient surface electric and magnetic fields. Two external electromagnetic (EM) signals were used in the AMT and magnetotelluric (MT) investigations. The magnetosphere and atmosphere release EM signals. Low-frequency MT signals are emitted by the solar wind, auroras, and Earth's magnetosphere. Around the world, high-frequency audio range (AMT) emissions (> 1 Hz) are produced by lightning and thunderstorms. In the crust of the Earth, EM signal exchanges produce horizontal telluric currents (Simpson and Bahr 2005). MT surveys measured magnetic signals and telluric currents. Using orthogonal sensors, the AMT examines the electric and magnetic changes caused by telluric currents. Time-series data was processed using the frequency domain method. In the measured field frequency domain, an estimate of the transfer function (complex impedance matrix) is made. Using forward modeling and inversion techniques, resistivity distribution models (1-D, 2-D, and 3-D) were created from the MT data. The isotope analysis results were confirmed by field testing using VES and AMT. The recharge and discharge locations provided the VES and AMT data. Six AMT and VES trajectory points were used. The data on the 18 O and 2 H isotope ratios from rainfall samples gathered in the recharge area—which is close to Mount Agung—was also used for verification. AIDU 2D software was used to assess the 2D ADMT Method survey from the Anbit ADMT-300HT2 Smart AMT instrument (Fig. 6 ). 3. Result and Discussion 3.1 Water sampling location Four places, each with a minimum elevation difference of 100 meters, were used to collect rainwater. At one point, the spring's outflow was also analyzed for spring water. Table 1 lists the sites where the samples were taken, and Fig. 7 shows those locations. Table 1 Position of Water Sample No. Location Coordinates Altitude (meter above sea level) Description Latitude (S) Longitude (E) 1 Ababi Spring 8° 23' 59" 115° 34' 58" 378 Spring water 2 Autotama 8° 25' 44" 115° 35' 31" 211 Rainwater 3 Ababi (below) 8° 23' 54" 115° 35' 0" 386 Rainwater 4 Ababi (above) 8° 23' 13" 115° 34' 2" 596 Rainwater 5 Tanah Aron 8° 22' 17" 115° 32' 38" 978 Rainwater Prior to any rainfall, a rainwater collection system was erected. The water sample was put in a firmly covered bottle to ensure there was no air inside when it had rained, and the amount of water collected was judged sufficient. Airtight bottles were employed to ensure that no air entered, and the water sample was carefully stored to prevent evaporation. After that, the sealed samples were sent to the Faculty of Mining and Petroleum Engineering at Bandung Institute of Technology's Hydrogeology and Hydrogeochemistry Laboratory for analysis. 3.2 Stable Isotopes Analysis Table 2 presents the results of tests conducted on rainwater and springwater samples. With results of -12.416‰ for (δD)SMOW and − 4.366‰ for (δ 18 O)SMOW, it suggests that the rainwater samples at low elevation (211 m above sea level) have a more enriched isotope composition. Nonetheless, the rainwater data from the high ground (978 m above sea level) show a more depleted isotope ratio, with a value of -39.748‰ for (δD)SMOW and − 7.706‰ for (δ 18 O)SMOW. Table 2 Data on the isotope ratios in samples of spring water and rains No Location Altitude (meter above sea level) δ 18 O (‰) δ 18 H (‰) 1 Spring water 378 -7,706 ± 0,008 -39,748 ± 0,211 2 Autotama 211 -4,366 ± 0,008 -12,416 ± 0,233 3 Ababi (below) 386 -4,163 ± 0,007 -11,642 ± 0,200 4 Ababi (above) 596 -4,592 ± 0,033 -13,262 ± 0,300 5 Tanah Aron 978 -4,749 ± 0.019 -14,365 ± 0.056 These findings confirm the hypothesis that the isotope composition of (δD) SMOW and (δ 18 O) SMOW rainwater is more depleted at higher elevations and vice versa. The term "altitude effect" is frequently used to describe this phenomenon (Anuard et al., 2019 ). The Local Meteoric Water Line (LMWL) graph for the Ababi area can be created by plotting the data on the change of the (δD) SMOW and (δ 18 O) SMOW isotope ratios of rainfall samples as a function of elevation in Table 2 on the δ 18 O‰–δD‰ graph. Eq. 7 is used to demonstrate this in Fig. 8 : δD = 4,4912 x δ 18 O + 7,1419 (7) with R 2 value = 0,9778. The Global Meteoric Water Line (GMWL) is situated above the LMWL, with δD = 8. δ 18 O + 10. This explains why the LMWL and GMWL were positioned differently: the isotope test values shown on the GMWL were derived from non-tropical climate zones. On the other hand, the climate of Indonesia, especially in Bali, is more tropical. The LMWL that developed was generally comparable to the GMWL. The 18O and 2H isotope composition values for the Ababi spring water samples were − 7.706 ± 0.008 and − 39.748 ± 0.211, respectively, according to the results of the isotope testing. The equal interval method was employed to classify the 18O and 2H isotope composition groupings. This method involves grouping the data values into similar ranges. The groundwater samples in the study area constituted distinct groups and were situated much below the local meteoric water line, as indicated by this classification (Fig. 8 ). The water samples were below the LMWL line when the 18 O and 2 H isotope compositions were plotted against the Ababi Spring line, proving that neighboring rains did not produce the water. The Ababi Spring water most likely comes from a rainfall sampling point or from a region higher up than the spring. 3.3 Calculating the Elevation of Ababi Spring Isotope testing results and the mapping of 18 O and 2 H isotope compositions against the LMWL line indicate that the Ababi Spring was not formed by local rainfall. It is expected to originate from a water source situated above Ababi Spring. Elevation was calculated using the link between 18O and the rainwater sample elevation. Groundwater is relevant to the application of 18O as an elevation determinant. The samples' isotopic composition was found to be lower than the standard, as shown by their negative 18 O and 2 H isotope prices. This procedure suggests that the recharge area naturally undergoes isotope fractionation (light and heavy) and evaporation after rainfall. The 18 O isotope composition with elevation in rainwater samples is shown in Table 3 . Table 3 Water samples analysis No Location Samples Altitude (meter above sea level) δ 18 O(%o) 1 Spring water Spring water 378 -7,706 ± 0,008 2 Autotama Rainwater 211 -4,366 ± 0,008 3 Ababi (below) Rainwater 386 -4,163 ± 0,007 4 Ababi (above) Rainwater 596 -4,592 ± 0,033 5 Tanah Aron Rainwater 978 -4,749 ± 0,019 Using solely rainfall samples, weighted regression provides the foundation for the Local Meteoric Water Line (LMWL). In hydrology, the weighted LMWL is advised as a more suitable input function. A weighted LMWL was employed to determine the input or make-up of the Ababi groundwater source. The association between the 18O isotope ratio and the height of the rainwater sample in Table 4 was found to be linear, as illustrated in Fig. 9 . This suggests that the 18O isotope ratio is reduced at higher elevations. Equation 8 displays the linear regression model that was created from the link between the elevation of the rainwater sample and the 18 O isotope ratio. δ 18 O‰ =-0,0006 x Altitude – 4,1174 (8) with R 2 value = 0,6847. Alternatively, it can be approximated using Eq. (9). Altitude = -1666,67 x δ 18 O‰ – 6862,33 (9) By inputting the water samples' isotope ratio (δ 18 O) value into Eq. 9, it is possible to forecast the recharge area of the Ababi Spring. Eq. 9 indicates that Ababi Spring is situated at a height of 378 meters above sea level, with a value of δ 18 O = -7.706 ± 0.008‰. This corresponds to the elevation of the Ababi Spring recharge region, which is 2.118,696-2.137,362 meters above sea level (Fig. 10 ). 3.4 Validation of the Water Flow Model Illustration from the Recharge to the Discharge Region In order to confirm the identification of infiltration zones, samples of rainwater were gathered from places that were thought to be recharging areas. The sites for rainwater collection, as well as those for Video Electron Sensor (VES) and Audio Magneto Telluric (AMT) data collecting for verification reasons, are depicted in Fig. 11 and Table 4 . Table 4 Location of VES and AMT surveys and water sample for verification No Location Coordinates Altitude (meter above sea level) Latitude Longitude 1 Tanah Aron 1 8° 21' 58" 115° 32' 58" 1300 2 Tanah Aron 2 8° 22' 3" 115° 32' 9" 1200 3 Tanah Aron 3 8° 22' 10" 115° 32' 22" 1089 4 Ababi 1 8° 23' 16" 115° 34' 17" 541 5 Ababi 2 8° 2' 22.2" 115° 34' 48" 425 6 Above Water Spring 8° 23' 53" 115° 35' 2" 387 The highest point at which rainwater could be collected was 1.514 meters above sea level. This is because the terrain is hilly and has outcrops of andesite rocks, which are volcanic lava rocks from Mount Agung. The 18 O and 2 H ratios were determined using extra information from rainwater samples collected in the Telaga Beteng region (Table 5 ). Table 5 Isotope testing results of water samples for verification No Location Coordinates Altitude δ 18 O (‰) δ 18 H (‰) Latitude Longitude 1 Telaga Beteng 8° 21' 46" 115° 31' 40" 1.514 -5,125 ± 0,008 -36,104 ± 0,211 To find the oxygen isotope equation at the same height as the Ababi Spring recharge area, insert this isotope ratio value into Eq. 9. This indicates that, as previously mentioned, the Ababi Spring recharge region in Karangasem is 2.118 meters above sea level. As a verification model, groundwater flow modeling was then carried out utilizing the VES and AMT techniques from the recharge area to the discharge area. Table 4 and Fig. 11 illustrate the six points at which the VES and AMT data were collected. Water flowing from the catchment region to the release area is assumed to be in strata with low resistivity, which are calculated based on the VES and AMT data and may represent aquifers or waterways (Figs. 12 and 13 ). 4. Conclusion The objective of this research was to ascertain the Ababi Spring's recharge area in Indonesia through a multidisciplinary strategy that included stable isotope studies, VES, and AMT techniques. Hydrogen and oxygen isotope ratios were measured in samples of spring and rainwater that were collected over an elevation gradient. Springwater originates from rainwater at a higher height of 2,118–2,137 m above sea level, according to the isotope data. Subsurface profiles consistent with groundwater flow from the elevated recharge area to the Ababi Spring outlet were produced by geoelectrical surveys employing VES and AMT techniques. The prediction model was validated by further isotope analysis of rainfall at a height of 1,514 meters. The key findings demonstrate that integrating multiple hydrochemical and geophysical methods enables more reliable delineation of groundwater recharge zones than individual techniques. The identified Ababi Spring recharge area will facilitate targeted conservation efforts to maintain this vital water resource. This combined methodology can be applied to effectively locate recharge areas of other springs and groundwater systems, especially in complex terrain. Further work should investigate the subsurface geochemical evolution of water along flow paths from recharge to discharge zones. Tracer experiments may also help validate and refine the groundwater flow model. Determining recharge areas is critical for science-based management of water resources to balance utilization and sustainability. Declarations The authors declare no conflicts of interest. Author Contribution INS developed research ideas for the VES and AMT surveys at the research location. IWR formulated the concept and design. PDHA and AANG collected and processed VES and AMT data. All authors drafted, proofread, and translated the manuscript into English. Acknowledgement The authors would like to thank DIPA PNBP Udayana University 2021 for funding this research, which was carried out in accordance with Research Implementation Assignment Agreement Letter Number B/96-244/UN14.4. A/PT.01.05/2021, dated May 03, 2021. Data availability The research data can be obtained based on request and approval from all authors. References Aguedai, H., Jelbi, M., Lahlou, F. & Abdelaziz, M. (2022) Hydrochemical and geophysical characterization of the Mnasra coastal aquifers (Rharb basin NW Morocco). Arabian Journal of Geosciences, 15, 1480, doi: 10.1007/s12517-022-10738-7 . Agyemang, V. O. (2022) Groundwater exploration by magnetotelluric method within the birimian rocks of mankessim, Ghana. Applied Water Science, 12, 1–6, doi: 10.1007/s13201-022-01576-9 . Ailes, C. E. & Rodriguez, B. D. (2014) Magnetotelluric Data Collected to Characterize Aquifers in the San Luis Basin, New Mexico Virginia pp. Anuard, P.-G., Julián, G.-T., Hugo, J.-F., Carlos, B.-C., Arturo, H.-A., Edith, O.-T. & Claudia, Á.-S. (2019) Integration of Isotopic (2H and 18O) and Geophysical Applications to Define a Groundwater Conceptual Model in Semiarid Regions. Water, 11, 488, doi: 10.3390/w11030488 . Ardana, P., Redana, W., Yekti, M. & Simpen, N. (2022) The Stable Isotopes Approach as Tracers to Investigate the Origin of Groundwater In The Unconfined Aquifer of Denpasar, Bali. Acta Montanistica Slovaca, 27, 968–981. Bai, E., Guo, W., Zhang, D., Tan, Y., Guo, M. & Zhao, G. (2019) Using the magnetotelluric method for detecting aquifer failure characteristics under high-intensity mining of thick coal seams. Energies, 12, doi: 10.3390/en12224397 . Blasch, K. W. & Bryson, J. R. (2007) Distinguishing Sources of Groundwater Recharge by Using δ2H and δ18O. Ground Water, 45, 294–308, doi: 10.1111/j.1745-6584.2006.00289.x . Chave, A. D. & Jones, A. G. (2012) The Magnetotelluric Method: Theory and practice. In : Chave, A. D. & Jones, A. G. (eds) The Magnetotelluric Method: Theory and Practice Cambridge University Press, Cambridge, iii–iii., doi: DOI: undefined. Chen, H., Niu, Q., Mendieta, A., Bradford, J. & McNamara, J. (2023) Geophysics-Informed Hydrologic Modeling of a Mountain Headwater Catchment for Studying Hydrological Partitioning in the Critical Zone. Water Resources Research, 59, doi: 10.1029/2023WR035280 . Clark, I. (2015) Groundwater Geochemistry and Isotopes CRC Press, Boca Raton pp. Dinas Pekerjaan Umum Provinsi Bali (2014) Laporan Akhir Laporan Akhir Pekerjaan Peta Zonasi Pemanfaatan Air Tanah Provinsi Bali Tahun Anggaran 2014 Denpasar pp. Eriksson, E. (1983) Guide Book on Nuclear Techniques in Hydrology. In : Guide Book on Nuclear Techniques in Hydrology International Atomic Energy Agency, Vienna, 19–33., doi: 10.1515/9783112517369-012 . Fajar, M. H. M., Utama, U. W., Akbar, F. S., Hilyah, A., Pandu, J., Rochman, G. N. & Purwanto, M. S. (2019) Penentuan Daerah Imbuhan Dengan Metode Analisis Isotop Air Tanah di Desa Cottok, Kec. Kapongan Kabupaten Situbondo. Jurnal Geosaintek, 5, 31–36. Goldscheider, N. & Drew, D. (2007) Methods in Karst Hydrogeology: IAH: International Contributions to Hydrogeology . 1st ed. CRC Press, London pp. Hamzah, U., Samsudin, A. R. & Malim, E. P. (2007) Groundwater investigation in Kuala Selangor using vertical electrical sounding (VES) surveys. Environmental Geology, 51, 1349–1359, doi: 10.1007/s00254-006-0433-8 . Hendrayana, H., Nuha, A., Wiyatna, A. B., Muhammad, A. S. & Engineering, G. (2019) Hydrogen Isotope Study to Determine Groundwater Genesis in Mambal Spring, Bali, Indonesia Location. In : 11th Regional Conference on Geological and Geo-Resources Engineering ‘Innovations and Emerging Technologies for Responsible Mineral Resource Development’ National Insitute of Geological Sciences, College of Science, University of the Philippines, Quezon City. Kendall, C. & Mcdonnell, J. J. (1998) Isotope Tracers in Catchment Hydrology . 1st ed. Elsevier B.V., 839 pp. Kresic, N. & Stevanovic, Z. (2010) Groundwater and Hydrology of Springs Butterworth-Heinemann, Burlington, 567 pp. Marfia, A. M., Krishnamurthy, R. V, Atekwana, E. A. & Panton, W. F. (2004) Isotopic and Geochemical Evolution of Ground and Surface Waters in a Karst Dominated Geological Setting: a Case StudyFrom Belize, Central America. Applied Geochemistry, 19, 937–946, doi: 10.1016/j.apgeochem.2003.10.013 . Maria, R., Satrio, Iskandarsyah, T. Y. W. M., Suganda, B. R., Delinom, R. M., Marganingrum, D., Purwoko, W., Sukmayadi, D. & Hendarmawan, H. (2021) Groundwater recharge area based on hydrochemical and environmental isotopes analysis in the south bandung volcanic area. Indonesian Journal of Chemistry, 21, 609–625, doi: 10.22146/ijc.58633 . Mazor, E. (2004) Chemical and Isotopic Groundwater Hydrology . 3rd Editio. Marcel Dekker Inc., New York pp. Mudiana, W. & Setiadi, H. (2008) Peta Sebaran Cekungan Air Tanah Pulau Bali Bandung pp. Mukherjee, A., Fryar, A. E. & Rowe, H. D. (2007) Regional-scale stable isotopic signatures of recharge and deep groundwater in the arsenic affected areas of West Bengal, India. Journal of Hydrology, 334, 151–161, doi: 10.1016/j.jhydrol.2006.10.004 . Ngene, B. U., Nwafor, C. O., Bamigboye, G. O., Ogbiye, A. S., Ogundare, J. O. & Akpan, V. E. (2021) Assessment of water resources development and exploitation in Nigeria: A review of integrated water resources management approach. Heliyon, 7, e05955, doi: 10.1016/j.heliyon.2021.e05955 . Nuha, A., Hendrayana, H., Wiyatna, A. B., Putra, D. P. E. & Muhammad, A. S. (2020) Determination of Groundwater Recharge Area by Using Hydroisotope Technic of Sei Bingei Area and Surrounding Areas, Langkat Regency, North Sumatra. Journal of Applied Geology, 5, 13, doi: 10.22146/jag.51627 . Palano, M. (2022) Editorial for the Special Issue: “Ground Deformation Patterns Detection by InSAR and GNSS Techniques”. Remote Sensing, 14, 1104, doi: 10.3390/rs14051104 . Pang, Z., Kong, Y., Li, J. & Tian, J. (2017) An Isotopic Geoindicator in the Hydrological Cycle. Procedia Earth and Planetary Science, 17, 534–537, doi: 10.1016/j.proeps.2016.12.135 . Pu, T., He, Y., Zhang, T., Wu, J., Zhu, G. & Chang, L. (2013) Isotopic and Geochemical Evolution of Ground and River Waters in a Karst Dominated Geological Setting: A Case Study From Lijiang Basin, South-Asia Monsoon Region. Applied Geochemistry, 33, 199–212, doi: 10.1016/j.apgeochem.2013.02.013 . Purbo-Hadiwidjojo, M. M., Samodra, H. & Amin, T. C. (1998) Peta Geologi Lembar Bali, Nusa Tenggara Bandung pp. Sánchez-Murillo, R., Brooks, E. S., Elliot, W. J. & Boll, J. (2015) Isotope Hydrology and Baseflow Geochemistry in Natural and Human-Altered Watersheds in the Inland Pacific Northwest, USA. Isotopes in Environmental and Health Studies, 51, 231–254, doi: 10.1080/10256016.2015.1008468 . Satrio, Prasetio, R., Hadian, M. S. D. & Syafri, I. (2017) Stable isotopes and hydrochemistry approach for determining the salinization pattern of shallow groundwater in alluvium deposit Semarang, Central Java. Indonesian Journal on Geoscience, 4, 1–10, doi: 10.17014/ijog.4.1.1-10 . Setiawan, T. & Asgaf, N. M. A. (2016) Analisis Karakteristik Akuifer dan Zonasi Kuantitas Air Tanah di Dataran Kars Wonosari dan Sekitarnya, Kabupaten Gunungkidul, Provinsi Daerah Istimewa Yogyakarta. Jurnal Lingkungan dan Bencana Geologi, 7, 155–167. Simpson, F. & Bahr, K. (2005a) Practical Magnetotellurics . Simpson, F. & Bahr, K. (eds) Cambridge University Press, Cambridge, 1–14 pp., doi: DOI: 10.1017/CBO9780511614095.002 . Simpson, F. & Bahr, K. (2005b) Practical Magnetotellurics Cambridge University Press, Cambridge pp., doi: 10.1017/CBO9780511614095 . Singh, M., Kumar, S., Kumar, B., Singh, S. & Singh, I. B. (2013) Investigation on the hydrodynamics of Ganga Alluvial Plain using environmental isotopes: a case study of the Gomati River Basin, Northern India. Hydrogeology Journal, 21, 687–700, doi: 10.1007/s10040-013-0958-3 . Sudadi, P., Setiadi, H., Denny, B. R., Arief, S., Ruchijat, S. & Hadi, S. (1986) Peta Hidrogeologi Lembar Pulau Bali Bandung pp. Suryadi, A., Putra, D. B. E., Kausarian, H., Prayitno, B. & Fahlepi, R. (2018) Groundwater exploration using Vertical Electrical Sounding (VES) Method at Toro Jaya, Langgam, Riau. Journal of Geoscience, Engineering, Environment, and Technology, 3, 226, doi: 10.24273/jgeet.2018.3.4.2226 . Toulier, A., Baud, B., de Montety, V., Lachassagne, P., Leonardi, V., Pistre, S., Dautria, J.-M., Hendrayana, H., Miftakhul Fajar, M. H., Satrya Muhammad, A., Beon, O. & Jourde, H. (2019) Multidisciplinary study with quantitative analysis of isotopic data for the assessment of recharge and functioning of volcanic aquifers: Case of Bromo-Tengger volcano, Indonesia. Journal of Hydrology: Regional Studies, 26, 100634, doi: https://doi.org/10.1016/j.ejrh.2019.100634 . Wijatna, A. B., Sudarmadji, Sunarno & Hendrayana, H. (2013) Studi Variabilitas Isotop Airhujan Sebagai Fungsi Elevasi untuk Mendapatkan Merapi Meteoric Water Line (MMWL). Forum Teknik, 35, 50–57. Yamashita, M. & Ii, H. (2016) Estimation of evaporation rate of surface water using hydrogen and oxygen isotopic ratios. International Journal of GEOMATE, 11, 2659–2664, doi: 10.21660/2016.26.5295 . Zamrsky, D., Oude Essink, G. H. P. & Bierkens, M. F. P. (2024) Global Impact of Sea Level Rise on Coastal Fresh Groundwater Resources. Earth’s Future, 12, doi: 10.1029/2023EF003581 . Zhou, R. X., Wang, J., Tang, C. J., Zhang, Y. P., Chen, X. A., Li, X., Shi, Y. Y., Wang, L., Xiao, H. B. & Shi, Z. H. (2023) Identifying soil water movement and water sources of subsurface flow at a hillslope using stable isotope technique. Agriculture, Ecosystems & Environment, 343, 108286, doi: 10.1016/j.agee.2022.108286 . Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4279145","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":293399759,"identity":"041cef5b-bf11-4586-a707-6d300ad6ad45","order_by":0,"name":"I N. Simpen","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAv0lEQVRIiWNgGAWjYDACZjBpAyIMQAQPwwHitKSRogUCDsO1MBDUIt/Onfbg447zidslkjcw/KhhkOEjpMXgMO92w5lnbifunJFWwNhzjIFHkqAWZt5t0rxttxM33MgxYOBtYOAxIOiwZqCWv23nwFoY/xKjheEwUAtj2wGwFmaibAH7pbct2XjDmWcFh2WOSRD2i3z/2W0PfrbZyW44nrzx4ZsaG3uCIQYEbHAWULEEYfUoWkbBKBgFo2AUYAUAUwRBk4YI9dkAAAAASUVORK5CYII=","orcid":"","institution":"Udayana University","correspondingAuthor":true,"prefix":"","firstName":"I","middleName":"N.","lastName":"Simpen","suffix":""},{"id":293399761,"identity":"eb03e26a-fd02-4f8a-8f3d-67ee72ed7c08","order_by":1,"name":"I W. Redana","email":"","orcid":"","institution":"Udayana University","correspondingAuthor":false,"prefix":"","firstName":"I","middleName":"W.","lastName":"Redana","suffix":""},{"id":293399763,"identity":"ca4ade4d-c904-41a3-884c-183c040df3a5","order_by":2,"name":"Putu D.H. Ardana","email":"","orcid":"","institution":"Ngurah Rai University","correspondingAuthor":false,"prefix":"","firstName":"Putu","middleName":"D.H.","lastName":"Ardana","suffix":""},{"id":293399765,"identity":"0b1e4b67-ebb8-42f8-83b0-9b947687af0f","order_by":3,"name":"Anak A.N. Gunawan","email":"","orcid":"","institution":"Udayana University","correspondingAuthor":false,"prefix":"","firstName":"Anak","middleName":"A.N.","lastName":"Gunawan","suffix":""}],"badges":[],"createdAt":"2024-04-17 03:59:28","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4279145/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4279145/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":55536594,"identity":"7427faea-ec28-4ce3-ab57-d241b0363197","added_by":"auto","created_at":"2024-04-29 16:36:10","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":631860,"visible":true,"origin":"","legend":"\u003cp\u003eResearch location\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-4279145/v1/1f1c3c307ad1c3f5d2911538.png"},{"id":55538638,"identity":"1cdf40a7-df17-41ad-9df4-06eb5a0138ad","added_by":"auto","created_at":"2024-04-29 16:52:10","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":596243,"visible":true,"origin":"","legend":"\u003cp\u003eAmlapura groundwater basin\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-4279145/v1/d258926eba328a91be138053.png"},{"id":55536596,"identity":"b0c55996-3a29-4c46-9948-2292b5d59b7d","added_by":"auto","created_at":"2024-04-29 16:36:10","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1036020,"visible":true,"origin":"","legend":"\u003cp\u003eIndonesian geology map in systematic form: Bali sheet\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-4279145/v1/6774b996c1a2e7609d7fd794.png"},{"id":55537585,"identity":"1ab99f17-196e-4f0e-a7d6-5dcba10565a7","added_by":"auto","created_at":"2024-04-29 16:44:10","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":276735,"visible":true,"origin":"","legend":"\u003cp\u003eIsotope \u003csup\u003e2\u003c/sup\u003eH and \u003csup\u003e18\u003c/sup\u003eO fractionation in hydrologic cycle\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-4279145/v1/24fce9230860c55404487fcc.png"},{"id":55537587,"identity":"9a37f032-bd2a-4718-807b-ed70d58b796a","added_by":"auto","created_at":"2024-04-29 16:44:10","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":279744,"visible":true,"origin":"","legend":"\u003cp\u003eEquipment of Vertical Electrical Sounding (VES) of geoelectrical method\u003c/p\u003e","description":"","filename":"image5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4279145/v1/e591d5dab783f339ebad10bd.jpeg"},{"id":55536599,"identity":"58256bc3-aec1-46fc-bb2f-be93a8904895","added_by":"auto","created_at":"2024-04-29 16:36:10","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":182439,"visible":true,"origin":"","legend":"\u003cp\u003eEquipment of audio magnetotelluric (AMT)\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-4279145/v1/2e0c73396a5ed4f38b50e0dc.png"},{"id":55537588,"identity":"69293630-6f8b-44a6-9ac8-b4c454ac9de9","added_by":"auto","created_at":"2024-04-29 16:44:10","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":100334,"visible":true,"origin":"","legend":"\u003cp\u003eWater sample position in the research area\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-4279145/v1/4951ea4e5d2e7f743e93dff9.png"},{"id":55536598,"identity":"c84d2362-32c1-43c4-abfe-ec5262ca08d1","added_by":"auto","created_at":"2024-04-29 16:36:10","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":31314,"visible":true,"origin":"","legend":"\u003cp\u003eLMWL and GMWL graph\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-4279145/v1/29d2ebbca56c490800d5fe38.png"},{"id":55536606,"identity":"e2ed1fcf-503a-4e30-80e9-1a8b5c2bf177","added_by":"auto","created_at":"2024-04-29 16:36:10","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":14114,"visible":true,"origin":"","legend":"\u003cp\u003ePlotting rainwater sample altitude and 18O isotopes\u003c/p\u003e","description":"","filename":"image9.png","url":"https://assets-eu.researchsquare.com/files/rs-4279145/v1/260efbeb8d2e1dc5eb19c3e3.png"},{"id":55536603,"identity":"6aab1434-6145-4449-8413-dd4b6e564dfb","added_by":"auto","created_at":"2024-04-29 16:36:10","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":87929,"visible":true,"origin":"","legend":"\u003cp\u003eAbabi spring recharge area\u003c/p\u003e","description":"","filename":"image10.png","url":"https://assets-eu.researchsquare.com/files/rs-4279145/v1/7bca53b85a8da8164c3bfbbc.png"},{"id":55537589,"identity":"98bbe85d-3c83-4606-9c9c-cda2ff5dbd42","added_by":"auto","created_at":"2024-04-29 16:44:10","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":77141,"visible":true,"origin":"","legend":"\u003cp\u003eLocations for collecting VES and AMT data as well as extra samples of rainwater\u003c/p\u003e","description":"","filename":"image11.png","url":"https://assets-eu.researchsquare.com/files/rs-4279145/v1/4507eaadd36677e526692a05.png"},{"id":55536604,"identity":"ac885596-3a7d-455e-85e8-1154cb12c4c7","added_by":"auto","created_at":"2024-04-29 16:36:10","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":426322,"visible":true,"origin":"","legend":"\u003cp\u003eResults of the water flow estimation based on VES data\u003c/p\u003e","description":"","filename":"image12.png","url":"https://assets-eu.researchsquare.com/files/rs-4279145/v1/eec377696ba5bd159ae7b695.png"},{"id":55536601,"identity":"754c3393-f7e9-4c18-a110-53e3c40e14af","added_by":"auto","created_at":"2024-04-29 16:36:10","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":650972,"visible":true,"origin":"","legend":"\u003cp\u003eUsing AMT data, the water flow estimate integrates findings across trajectories.\u003c/p\u003e","description":"","filename":"image13.png","url":"https://assets-eu.researchsquare.com/files/rs-4279145/v1/57971d348f263a65a33c7786.png"},{"id":56730312,"identity":"1c8a9313-ad61-49f2-b8bd-7964c0eb1531","added_by":"auto","created_at":"2024-05-19 11:31:43","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5022542,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4279145/v1/9d7b05fb-e843-4708-9482-96377d948611.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Identifying spring recharge areas using stable isotope and geophysical methods: A case study of the Ababi Mountain Region, Bali, Indonesia","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe depletion of water supplies is one of the most significant environmental issues of the twenty-first century (Ngene et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). One natural resource that is essential to human development and survival is water. It's getting harder and harder to find natural resources, particularly water (Yamashita \u0026amp; Ii, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Every day, the amount of water used increases in tandem with the rate of population expansion. The preservation of groundwater resources, especially springs, depends on the position of recharge regions. The stable isotope approach can be used to define locations that receive spring recharge and groundwater. Several Indonesian regions\u0026mdash;Bali in particular\u0026mdash;have used the isotopic technique to determine groundwater genesis (Maria et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Nuha et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Toulier et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), particularly in Bali. The application of isotope 18O and 2H methods in Denpasar City to delineate the groundwater recharge zone in urban areas (Ardana et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). It also entails figuring out where springs recharge, which is the main supply of untreated mineral water in the Mambal region (Hendrayana et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOxygen and hydrogen form water, and both elements have isotopes. Conservatism makes \u003csup\u003e18\u003c/sup\u003eO and \u003csup\u003e2\u003c/sup\u003eH natural tracers (Pu et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; S\u0026aacute;nchez-Murillo et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Low-temperature water-rock interactions do not influence them (Marfia et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Unaffected by harsh weather, rainwater from the top of the mountain or upstream region percolates through the soil until it reaches the land surface downstream. Wijatna et al. (\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) state that groundwater downstream (in wells or springs) will have oxygen and hydrogen isotope values similar to upstream precipitation. Because of this, the oxygen and hydrogen isotope levels of wells or springs from higher-elevation water recharge sites are lower than those from local rainfall. Therefore, local rainwater springs can be distinguished from higher-elevation catchment springs by their quantities of oxygen and hydrogen isotopes. This occurrence has motivated the use of natural isotopes as tracers to investigate the water dynamics of the hydrological cycle. To detect recharge and flow zones, isotopes are combined with groundwater from different sources and used as tracers in groundwater research (Blasch \u0026amp; Bryson, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Mukherjee et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Singh et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Setiawan \u0026amp; Asgaf, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePrevious hydrogeological studies of the Ababi Spring system are limited. Toulier et al. (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) applied isotope techniques to study the recharge processes of springs connected to Indonesia's Bromo-Tengger volcanic aquifer system but did not specifically focus on the Ababi Spring. Maria et al. (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) also used hydrochemistry and environmental isotopes to delineate groundwater recharge areas in the South Bandung volcanic region but did not consider geophysical approaches. To date, no studies have combined stable isotope analysis with geoelectrical methods to map the recharge area of Ababi Spring. Several knowledge gaps remain regarding the origin and subsurface flow pathways of water discharging from this vital spring. This study addresses these gaps using an integrated approach coupling isotope hydrology and geophysics to delineate the recharge area effectively. The findings will aid water conservation efforts for the spring.\u003c/p\u003e \u003cp\u003eHydrogeological studies have revealed rocks and structural links up to a depth of 300 m (Agyemang, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Ailes \u0026amp; Rodriguez (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2014\u003c/span\u003e) identified aquifers in the San Luis Basin in New Mexico using the magnetotelluric methodology, and Bai et al. (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) found overloaded structures and aquifers using the same method. To the best of our knowledge, it is challenging, costly, and impracticable to determine the recharge area of springs or groundwater using geochemical or geophysical approaches. This work combines the isotope technique, vertical electrical resistivity (VES) method, and magnetotelluric (audio magnetotelluric) method to measure the recharge area of the spring, thereby resolving the shortcomings of the previously mentioned methodologies. In the hilly Ababi Area, Abang District, Karangasem, spring catchment zones were identified using this methodology. This reservoir is the main water supply for the urban drinking water delivery system (PDAM) in the Karangasem District. The Ababi Spring's catchment area can be understood in order to carry out effective and efficient spring recharge area conservation efforts, ensuring the springs' continued existence. Determining groundwater recharge areas from traditional hydrogeological data alone poses significant challenges (Zamrsky et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). While isotope techniques can trace water sources (Zhou et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), they do not delineate subsurface flow paths. Conversely, geophysical surveys map subsurface structures but cannot independently identify hydrologic connections (Chen et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThis study utilizes a novel combination of stable isotope analysis, vertical electrical sounding (VES), and audio magnetotelluric (AMT) surveys to provide independent yet mutually consistent lines of evidence for mapping the recharge provenance and subsurface flow regime of the Ababi Spring. The convergence of geochemistry and geophysics facilitates more reliable groundwater basin characterization (Aguedai et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), especially in complex volcanic terrains. To date, this specific integrated approach has not been applied to delineate the Ababi Spring\u0026rsquo;s recharge area, representing an essential knowledge advancement.\u003c/p\u003e \u003cp\u003eTherefore, this study aims to determine the recharge area and origin of the Ababi Spring using isotope techniques and validate flow connections to the identified recharge zone using geoelectrical surveys. The overarching goal is delineating the spring catchment to support long-term sustainable management. The technical approach integrates stable 2H and 18O isotope analysis, VES, and AMT methods. Isotope hydrology traces input water sources, while geophysics maps geological structures and hydrostratigraphy (Palano, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). This study represents the first application combining these specific techniques to effectively and reliably characterize the Ababi Spring recharge system.\u003c/p\u003e"},{"header":"2. Methodology","content":"\u003cp\u003eThe research employed various techniques, including data collection, calculations, analysis, and verification. Hydrogeological conditions, isotope ratio computations, and geoelectric and magnetotelluric interpretations were used to validate spring catchment regions. The study commenced with a literature review, the gathering of secondary data, and a field study to locate springs and other water sources. Indonesia\u0026rsquo;s Ministry of Energy and Mineral Resources published groundwater basin, hydrogeological, and geological maps, which were used in the study.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Study Sites\u003c/h2\u003e \u003cp\u003eAbabi Village is located in Abang District, Karangasem Regency, Bali Province, and boasts a spring at 8\u0026deg; 24' 8.14\" S and 115\u0026deg; 35' 12.85\" E (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Lake Batur extends further northwest, while Mount Agung is located northwest of the Ababi Spring. Ababi Village, spanning 10.86 km\u0026sup2; and with an average elevation of 573 m above sea level (ASL), is a distinct and lovely place. Generally speaking, the village area is situated at the base of Mount Agung, with a Southeast-facing land slope. The tallest region is in the north, while modest hills, primarily rice fields, may be found in the east and center. There are plains to the west and south. The range of daytime temperatures was 29 to 35\u0026deg;C.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Hydrogeological environment\u003c/h2\u003e \u003cp\u003eThe Amlapura groundwater basin includes Ababi Village (Mudiana \u0026amp; Setiadi, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The Amlapura groundwater basin occupies an area of roughly 213.6 km2 and is situated in the Karangasem Regency in the eastern portion of Bali Province. With an average annual rainfall of 1,000 to 3,500 mm, it has a shallow groundwater potential of around 60\u0026nbsp;million m3/year and a profound groundwater potential of about 2\u0026nbsp;million m3/year. The basin's radial river flow pattern originates at the volcanic cone and expands outward in all directions, creating plains, rolling hills, and volcanic cones as morphological units. The basin's topographic elevation ranges from 0 to 3,500 m above sea level (Dinas Pekerjaan Umum Provinsi Bali, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe main lithology of this basin, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, is alluvium deposits found in rivers and on beaches, which serve as an aquifer, which are primarily made up of medium-gradient sand and gravel; Agung volcanic rocks (Qhva), which are primarily made up of medium-gradient agglomerates, tuffs, lavas, and lahar deposits; and Seraya volcano rocks (Qvps), which are made up of low-gradient volcanic breccia and lava. (Purbo-Hadiwidjojo et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). A spring with a 5 l/s discharge rate is present (Sudadi et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1986\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Stable Isotopes\u003c/h2\u003e \u003cp\u003eSun-evaporated seawater initiates hydrological cycles by becoming airborne through evaporation, with the wind subsequently carrying it to various locations such as the land, aquifers, rivers, lakes, and back to the sea. As the altitude decreases, the air pressure decreases, with mountains having a lower air pressure than the coast. Water-laden air rises or falls under atmospheric pressure, which affects the movement of water in the hydrological cycle. Height decreases the water-laden air temperature (lapse rate). Hydrogeologists use water-forming isotopes such as hydrogen (\u003csup\u003e1\u003c/sup\u003eH, \u003csup\u003e2\u003c/sup\u003eH, and \u003csup\u003e3\u003c/sup\u003eH) and oxygen (\u003csup\u003e16\u003c/sup\u003eO, \u003csup\u003e17\u003c/sup\u003eO, and \u003csup\u003e18\u003c/sup\u003eO) (Mazor, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Goldscheider \u0026amp; Drew, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The evaporated water had the following hydrogen and oxygen isotopes: 1H 99.985%, \u003csup\u003e2\u003c/sup\u003eH 0.015%, and \u003csup\u003e3\u003c/sup\u003eH less than 0.001%; \u003csup\u003e16\u003c/sup\u003eO 99.63%, \u003csup\u003e17\u003c/sup\u003eO 0.0375%, and \u003csup\u003e18\u003c/sup\u003eO 0.1995%. \u003csup\u003e16\u003c/sup\u003eO and \u003csup\u003e2\u003c/sup\u003eH precipitation decrease by 0.15\u0026ndash;0.5 and 1\u0026ndash;4 per 100 m in elevation, respectively (Clark, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe D/1H and 18O/16O isotope ratios in water measured very low relative abundances (R) of \u003csup\u003e18\u003c/sup\u003eO and \u003csup\u003e2\u003c/sup\u003eH (or deuterium\u0026thinsp;=\u0026thinsp;D). R\u003csub\u003eStd\u003c/sub\u003e, SMOW, or seawater's D/1H or 18O/16O isotope ratios were compared. The ocean has the most significant evaporation process in the hydrological cycle; therefore, seawater has been used internationally as a reference. Most water samples (excluding seawater) had negative D and 18O isotopes. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the hydrological cycle D and \u003csup\u003e18\u003c/sup\u003eO isotope fractionation (Pang et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Kresic \u0026amp; Stevanovic, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Mazor, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). In units of \u0026permil; (per mil), the notations (δD)SMOW and (δ\u003csup\u003e18\u003c/sup\u003eO)SMOW are denoted as (δD) and (δ\u003csup\u003e18\u003c/sup\u003eO), respectively. δ\u003csub\u003esmpl\u003c/sub\u003e was used to express the sample isotopes' relative abundance (Nuha et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2020\u003c/span\u003e):\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\text{\u0026delta;}}_{\\text{sample}}\\text{= }\\frac{{\\text{R}}_{\\text{sample}}\\text{-}{\\text{R}}_{\\text{std}}\\text{ }}{{\\text{R}}_{\\text{std}}}\\text{ x 100\\%}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe relative abundances of the samples were the \u003csup\u003e18\u003c/sup\u003eO/\u003csup\u003e16\u003c/sup\u003eO and \u003csup\u003e2\u003c/sup\u003eH/\u003csup\u003e1\u003c/sup\u003eH isotope ratios, where R\u003csub\u003eStd\u003c/sub\u003e is the SMOW standard ratio. The \u003csup\u003e18\u003c/sup\u003eO and \u003csup\u003e2\u003c/sup\u003eH concentrations of the hydrological cycle vary due to these water isotopes' freezing points and vapor pressures. Evaporation, condensation, freezing, thawing, chemical reactions, and biological processes can cause isotope fractionation (Pang et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Unless altered by magma, mixing, or evaporation, groundwater's \u003csup\u003e18\u003c/sup\u003eO and \u003csup\u003e2\u003c/sup\u003eH concentrations lie along the local meteoric line (rainwater). The straight line for rainwater differs from the \u003csup\u003e18\u003c/sup\u003eO and \u003csup\u003e2\u003c/sup\u003eH graphs.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eElevation and precipitation frequencies affected the D/\u003csup\u003e18\u003c/sup\u003eO isotope ratios. (D) and (\u003csup\u003e18\u003c/sup\u003eO) increase with decreasing frequency and precipitation. Rain and precipitation frequency affect (D) and (\u003csup\u003e18\u003c/sup\u003eO) at each sampling site; hence, equations 2 and 3 must be used to calculate the average value (Kresic \u0026amp; Stevanovic, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Clark, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2015\u003c/span\u003e):\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabb\" border=\"1\"\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\text{\u0026delta;}}^{\\text{18}}\\text{O= }\\frac{\\sum _{\\text{i=1}}^{\\text{n}}{\\text{P}}_{\\text{i}}{\\text{\u0026delta;}}_{\\text{i}}\\text{18}\\text{O}}{\\sum _{\\text{i=1}}^{\\text{n}}{\\text{P}}_{\\text{i}}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(2)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({\\text{\u0026delta;}}^{\\text{2}}\\text{H= }\\frac{\\sum _{\\text{i=1}}^{\\text{n}}{\\text{P}}_{\\text{i}}{\\text{\u0026delta;}}_{\\text{i}}\\text{2}\\text{H}}{\\sum _{\\text{i=1}}^{\\text{n}}{\\text{P}}_{\\text{i}}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003ewhere the following are included in the data set: Pi is the rainfall quantity between samples (i-1) and (i) (mm per month), δ\u003csub\u003ei\u003c/sub\u003e\u003csup\u003e18\u003c/sup\u003eO is the isotopic ratio of \u003csup\u003e18\u003c/sup\u003eO to SMOW in rainfall to (i) (\u0026permil;), and δ\u003csub\u003ei\u003c/sub\u003e\u003csup\u003e2\u003c/sup\u003eH is the isotopic ratio of \u003csup\u003e2\u003c/sup\u003eH close to SMOW in rainwater to (i) (\u0026permil;).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Electricity Sounding Vertically (VES)\u003c/h2\u003e \u003cp\u003eThe VES measures the electrical resistance. Surveys measuring electrical resistivity provide direct current between the electrodes while evaluating the potential between them. The current penetration matched the electrode distance. Resistance stratification is visible in the electrode spacing (Hamzah et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The Naniura NRD-300 HF was used for the VES survey, along with a laptop, electrodes, a machine, a cable, a connector, and a clamp (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Four straight-lined electrodes were spaced differently. Four electrodes require 200 m of wire, while 2 m are required. The two outer electrodes are currents, and the two inside electrodes have potential in a Schlumberger array (Koefoed). The spacing of the current electrode was 2\u0026ndash;200 m (AB/2\u0026thinsp;=\u0026thinsp;1\u0026ndash;100 m). 0.5\u0026ndash;10 m separated potential electrodes (MN). Changes in the electrode spacing between measurements were collected from field data (Hamzah et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). According to Suryadi et al. (\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), the resistivity value can be differentiated or partitioned using the master curve developed by Schlumberger. Plotting the apparent resistivity on a graph log was the first step, after which the shape of the plotted apparent resistivity was compared or approximated by looking for a curve. The master curve can be used to calculate the resistivity and thickness partition.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Audio Magnetotelluric (AMT)\u003c/h2\u003e \u003cp\u003eAn audio magnetotelluric (AMT) passive geophysical investigation utilizes high-frequency electromagnetic pulses ranging from 000 to 5 Hz to explore shallow to intense subsurface electrical conductivity. The AMT method determines subsurface electrical conductivity by measuring electromagnetic waves produced by the earth (Chave \u0026amp; Jones, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Simpson \u0026amp; Bahr, 2005). The subsurface electrical conductivity of Earth is estimated via the electromagnetic passive-source inductive audio magnetotelluric model. Subsurface conductivity was measured using transient surface electric and magnetic fields. Two external electromagnetic (EM) signals were used in the AMT and magnetotelluric (MT) investigations. The magnetosphere and atmosphere release EM signals. Low-frequency MT signals are emitted by the solar wind, auroras, and Earth's magnetosphere. Around the world, high-frequency audio range (AMT) emissions (\u0026gt;\u0026thinsp;1 Hz) are produced by lightning and thunderstorms. In the crust of the Earth, EM signal exchanges produce horizontal telluric currents (Simpson and Bahr 2005). MT surveys measured magnetic signals and telluric currents.\u003c/p\u003e \u003cp\u003eUsing orthogonal sensors, the AMT examines the electric and magnetic changes caused by telluric currents. Time-series data was processed using the frequency domain method. In the measured field frequency domain, an estimate of the transfer function (complex impedance matrix) is made. Using forward modeling and inversion techniques, resistivity distribution models (1-D, 2-D, and 3-D) were created from the MT data. The isotope analysis results were confirmed by field testing using VES and AMT. The recharge and discharge locations provided the VES and AMT data. Six AMT and VES trajectory points were used. The data on the \u003csup\u003e18\u003c/sup\u003eO and \u003csup\u003e2\u003c/sup\u003eH isotope ratios from rainfall samples gathered in the recharge area\u0026mdash;which is close to Mount Agung\u0026mdash;was also used for verification. AIDU 2D software was used to assess the 2D ADMT Method survey from the Anbit ADMT-300HT2 Smart AMT instrument (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Result and Discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Water sampling location\u003c/h2\u003e \u003cp\u003eFour places, each with a minimum elevation difference of 100 meters, were used to collect rainwater. At one point, the spring's outflow was also analyzed for spring water. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e lists the sites where the samples were taken, and Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e shows those locations.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePosition of Water Sample\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eNo.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eLocation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eCoordinates\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eAltitude\u003c/p\u003e \u003cp\u003e(meter above sea level)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eDescription\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLatitude (S)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLongitude (E)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAbabi Spring\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u0026deg; 23' 59\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e115\u0026deg; 34' 58\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e378\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSpring water\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAutotama\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u0026deg; 25' 44\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e115\u0026deg; 35' 31\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e211\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRainwater\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAbabi (below)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u0026deg; 23' 54\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e115\u0026deg; 35' 0\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e386\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRainwater\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAbabi (above)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u0026deg; 23' 13\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e115\u0026deg; 34' 2\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e596\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRainwater\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTanah Aron\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u0026deg; 22' 17\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e115\u0026deg; 32' 38\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e978\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRainwater\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003ePrior to any rainfall, a rainwater collection system was erected. The water sample was put in a firmly covered bottle to ensure there was no air inside when it had rained, and the amount of water collected was judged sufficient. Airtight bottles were employed to ensure that no air entered, and the water sample was carefully stored to prevent evaporation. After that, the sealed samples were sent to the Faculty of Mining and Petroleum Engineering at Bandung Institute of Technology's Hydrogeology and Hydrogeochemistry Laboratory for analysis.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Stable Isotopes Analysis\u003c/h2\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e presents the results of tests conducted on rainwater and springwater samples. With results of -12.416\u0026permil; for (δD)SMOW and \u0026minus;\u0026thinsp;4.366\u0026permil; for (δ\u003csup\u003e18\u003c/sup\u003eO)SMOW, it suggests that the rainwater samples at low elevation (211 m above sea level) have a more enriched isotope composition. Nonetheless, the rainwater data from the high ground (978 m above sea level) show a more depleted isotope ratio, with a value of -39.748\u0026permil; for (δD)SMOW and \u0026minus;\u0026thinsp;7.706\u0026permil; for (δ\u003csup\u003e18\u003c/sup\u003eO)SMOW.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eData on the isotope ratios in samples of spring water and rains\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLocation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAltitude\u003c/p\u003e \u003cp\u003e(meter above sea level)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eδ\u003csup\u003e18\u003c/sup\u003eO (\u0026permil;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eδ\u003csup\u003e18\u003c/sup\u003eH (\u0026permil;)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpring water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e378\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e-7,706\u0026thinsp;\u0026plusmn;\u0026thinsp;0,008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e-39,748\u0026thinsp;\u0026plusmn;\u0026thinsp;0,211\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAutotama\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e211\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e-4,366\u0026thinsp;\u0026plusmn;\u0026thinsp;0,008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e-12,416\u0026thinsp;\u0026plusmn;\u0026thinsp;0,233\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAbabi (below)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e386\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e-4,163\u0026thinsp;\u0026plusmn;\u0026thinsp;0,007\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e-11,642\u0026thinsp;\u0026plusmn;\u0026thinsp;0,200\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAbabi (above)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e596\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e-4,592\u0026thinsp;\u0026plusmn;\u0026thinsp;0,033\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e-13,262\u0026thinsp;\u0026plusmn;\u0026thinsp;0,300\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTanah Aron\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e978\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e-4,749\u0026thinsp;\u0026plusmn;\u0026thinsp;0.019\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e-14,365\u0026thinsp;\u0026plusmn;\u0026thinsp;0.056\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThese findings confirm the hypothesis that the isotope composition of (δD) SMOW and (δ\u003csup\u003e18\u003c/sup\u003eO) SMOW rainwater is more depleted at higher elevations and vice versa. The term \"altitude effect\" is frequently used to describe this phenomenon (Anuard et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The Local Meteoric Water Line (LMWL) graph for the Ababi area can be created by plotting the data on the change of the (δD) SMOW and (δ\u003csup\u003e18\u003c/sup\u003eO) SMOW isotope ratios of rainfall samples as a function of elevation in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e on the δ\u003csup\u003e18\u003c/sup\u003eO\u0026permil;\u0026ndash;δD\u0026permil; graph. Eq.\u0026nbsp;7 is used to demonstrate this in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e:\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabc\" border=\"1\"\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eδD\u0026thinsp;=\u0026thinsp;4,4912 x δ\u003csup\u003e18\u003c/sup\u003eO + 7,1419\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(7)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003ewith R\u003csup\u003e2\u003c/sup\u003e value\u0026thinsp;=\u0026thinsp;0,9778.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Global Meteoric Water Line (GMWL) is situated above the LMWL, with δD\u0026thinsp;=\u0026thinsp;8. δ\u003csup\u003e18\u003c/sup\u003eO + 10. This explains why the LMWL and GMWL were positioned differently: the isotope test values shown on the GMWL were derived from non-tropical climate zones. On the other hand, the climate of Indonesia, especially in Bali, is more tropical. The LMWL that developed was generally comparable to the GMWL. The 18O and 2H isotope composition values for the Ababi spring water samples were \u0026minus;\u0026thinsp;7.706\u0026thinsp;\u0026plusmn;\u0026thinsp;0.008 and \u0026minus;\u0026thinsp;39.748\u0026thinsp;\u0026plusmn;\u0026thinsp;0.211, respectively, according to the results of the isotope testing. The equal interval method was employed to classify the 18O and 2H isotope composition groupings. This method involves grouping the data values into similar ranges. The groundwater samples in the study area constituted distinct groups and were situated much below the local meteoric water line, as indicated by this classification (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). The water samples were below the LMWL line when the \u003csup\u003e18\u003c/sup\u003eO and \u003csup\u003e2\u003c/sup\u003eH isotope compositions were plotted against the Ababi Spring line, proving that neighboring rains did not produce the water. The Ababi Spring water most likely comes from a rainfall sampling point or from a region higher up than the spring.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Calculating the Elevation of Ababi Spring\u003c/h2\u003e \u003cp\u003eIsotope testing results and the mapping of \u003csup\u003e18\u003c/sup\u003eO and \u003csup\u003e2\u003c/sup\u003eH isotope compositions against the LMWL line indicate that the Ababi Spring was not formed by local rainfall. It is expected to originate from a water source situated above Ababi Spring. Elevation was calculated using the link between 18O and the rainwater sample elevation. Groundwater is relevant to the application of 18O as an elevation determinant. The samples' isotopic composition was found to be lower than the standard, as shown by their negative \u003csup\u003e18\u003c/sup\u003eO and \u003csup\u003e2\u003c/sup\u003eH isotope prices. This procedure suggests that the recharge area naturally undergoes isotope fractionation (light and heavy) and evaporation after rainfall. The \u003csup\u003e18\u003c/sup\u003eO isotope composition with elevation in rainwater samples is shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eWater samples analysis\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLocation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAltitude\u003c/p\u003e \u003cp\u003e(meter above sea level)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eδ\u003csup\u003e18\u003c/sup\u003eO(%o)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpring water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSpring water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e378\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e-7,706\u0026thinsp;\u0026plusmn;\u0026thinsp;0,008\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAutotama\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRainwater\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e211\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e-4,366\u0026thinsp;\u0026plusmn;\u0026thinsp;0,008\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAbabi (below)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRainwater\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e386\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e-4,163\u0026thinsp;\u0026plusmn;\u0026thinsp;0,007\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAbabi (above)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRainwater\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e596\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e-4,592\u0026thinsp;\u0026plusmn;\u0026thinsp;0,033\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTanah Aron\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRainwater\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e978\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e-4,749\u0026thinsp;\u0026plusmn;\u0026thinsp;0,019\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eUsing solely rainfall samples, weighted regression provides the foundation for the Local Meteoric Water Line (LMWL). In hydrology, the weighted LMWL is advised as a more suitable input function. A weighted LMWL was employed to determine the input or make-up of the Ababi groundwater source. The association between the 18O isotope ratio and the height of the rainwater sample in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e was found to be linear, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. This suggests that the 18O isotope ratio is reduced at higher elevations.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eEquation 8 displays the linear regression model that was created from the link between the elevation of the rainwater sample and the \u003csup\u003e18\u003c/sup\u003eO isotope ratio.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabd\" border=\"1\"\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eδ\u003csup\u003e18\u003c/sup\u003eO\u0026permil; =-0,0006 x Altitude \u0026ndash; 4,1174\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(8)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003ewith R\u003csup\u003e2\u003c/sup\u003e value\u0026thinsp;=\u0026thinsp;0,6847. Alternatively, it can be approximated using Eq.\u0026nbsp;(9).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabe\" border=\"1\"\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAltitude = -1666,67 x δ\u003csup\u003e18\u003c/sup\u003eO\u0026permil; \u0026ndash; 6862,33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(9)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eBy inputting the water samples' isotope ratio (δ\u003csup\u003e18\u003c/sup\u003eO) value into Eq.\u0026nbsp;9, it is possible to forecast the recharge area of the Ababi Spring. Eq.\u0026nbsp;9 indicates that Ababi Spring is situated at a height of 378 meters above sea level, with a value of δ\u003csup\u003e18\u003c/sup\u003eO = -7.706\u0026thinsp;\u0026plusmn;\u0026thinsp;0.008\u0026permil;. This corresponds to the elevation of the Ababi Spring recharge region, which is 2.118,696-2.137,362 meters above sea level (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Validation of the Water Flow Model Illustration from the Recharge to the Discharge Region\u003c/h2\u003e \u003cp\u003eIn order to confirm the identification of infiltration zones, samples of rainwater were gathered from places that were thought to be recharging areas. The sites for rainwater collection, as well as those for Video Electron Sensor (VES) and Audio Magneto Telluric (AMT) data collecting for verification reasons, are depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e and Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eLocation of VES and AMT surveys and water sample for verification\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eLocation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eCoordinates\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eAltitude\u003c/p\u003e \u003cp\u003e(meter above sea level)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLatitude\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLongitude\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTanah Aron 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u0026deg; 21' 58\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e115\u0026deg; 32' 58\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1300\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTanah Aron 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u0026deg; 22' 3\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e115\u0026deg; 32' 9\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1200\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTanah Aron 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u0026deg; 22' 10\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e115\u0026deg; 32' 22\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1089\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAbabi 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u0026deg; 23' 16\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e115\u0026deg; 34' 17\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e541\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAbabi 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u0026deg; 2' 22.2\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e115\u0026deg; 34' 48\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e425\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAbove Water Spring\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u0026deg; 23' 53\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e115\u0026deg; 35' 2\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e387\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe highest point at which rainwater could be collected was 1.514 meters above sea level. This is because the terrain is hilly and has outcrops of andesite rocks, which are volcanic lava rocks from Mount Agung. The \u003csup\u003e18\u003c/sup\u003eO and \u003csup\u003e2\u003c/sup\u003eH ratios were determined using extra information from rainwater samples collected in the Telaga Beteng region (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eIsotope testing results of water samples for verification\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eNo\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eLocation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eCoordinates\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eAltitude\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eδ\u003csup\u003e18\u003c/sup\u003eO (\u0026permil;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eδ\u003csup\u003e18\u003c/sup\u003eH (\u0026permil;)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLatitude\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLongitude\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTelaga Beteng\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u0026deg; 21' 46\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e115\u0026deg; 31' 40\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.514\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c6\"\u003e \u003cp\u003e-5,125\u0026thinsp;\u0026plusmn;\u0026thinsp;0,008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c7\"\u003e \u003cp\u003e-36,104\u0026thinsp;\u0026plusmn;\u0026thinsp;0,211\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo find the oxygen isotope equation at the same height as the Ababi Spring recharge area, insert this isotope ratio value into Eq.\u0026nbsp;9. This indicates that, as previously mentioned, the Ababi Spring recharge region in Karangasem is 2.118 meters above sea level.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs a verification model, groundwater flow modeling was then carried out utilizing the VES and AMT techniques from the recharge area to the discharge area. Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e illustrate the six points at which the VES and AMT data were collected. Water flowing from the catchment region to the release area is assumed to be in strata with low resistivity, which are calculated based on the VES and AMT data and may represent aquifers or waterways (Figs.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e and \u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e13\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThe objective of this research was to ascertain the Ababi Spring's recharge area in Indonesia through a multidisciplinary strategy that included stable isotope studies, VES, and AMT techniques. Hydrogen and oxygen isotope ratios were measured in samples of spring and rainwater that were collected over an elevation gradient. Springwater originates from rainwater at a higher height of 2,118\u0026ndash;2,137 m above sea level, according to the isotope data. Subsurface profiles consistent with groundwater flow from the elevated recharge area to the Ababi Spring outlet were produced by geoelectrical surveys employing VES and AMT techniques. The prediction model was validated by further isotope analysis of rainfall at a height of 1,514 meters.\u003c/p\u003e \u003cp\u003eThe key findings demonstrate that integrating multiple hydrochemical and geophysical methods enables more reliable delineation of groundwater recharge zones than individual techniques. The identified Ababi Spring recharge area will facilitate targeted conservation efforts to maintain this vital water resource. This combined methodology can be applied to effectively locate recharge areas of other springs and groundwater systems, especially in complex terrain. Further work should investigate the subsurface geochemical evolution of water along flow paths from recharge to discharge zones. Tracer experiments may also help validate and refine the groundwater flow model. Determining recharge areas is critical for science-based management of water resources to balance utilization and sustainability.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eThe authors declare no conflicts of interest.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eINS developed research ideas for the VES and AMT surveys at the research location. IWR formulated the concept and design. PDHA and AANG collected and processed VES and AMT data. All authors drafted, proofread, and translated the manuscript into English.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors would like to thank DIPA PNBP Udayana University 2021 for funding this research, which was carried out in accordance with Research Implementation Assignment Agreement Letter Number B/96-244/UN14.4. A/PT.01.05/2021, dated May 03, 2021.\u003c/p\u003e\u003ch2\u003eData availability\u003c/h2\u003e \u003cp\u003eThe research data can be obtained based on request and approval from all authors.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAguedai, H., Jelbi, M., Lahlou, F. \u0026amp; Abdelaziz, M. (2022) Hydrochemical and geophysical characterization of the Mnasra coastal aquifers (Rharb basin NW Morocco). Arabian Journal of Geosciences, 15, 1480, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s12517-022-10738-7\u003c/span\u003e\u003cspan address=\"10.1007/s12517-022-10738-7\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAgyemang, V. O. (2022) Groundwater exploration by magnetotelluric method within the birimian rocks of mankessim, Ghana. Applied Water Science, 12, 1\u0026ndash;6, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s13201-022-01576-9\u003c/span\u003e\u003cspan address=\"10.1007/s13201-022-01576-9\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAiles, C. E. \u0026amp; Rodriguez, B. D. (2014) \u003cem\u003eMagnetotelluric Data Collected to Characterize Aquifers in the San Luis Basin, New Mexico\u003c/em\u003e Virginia pp.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAnuard, P.-G., Juli\u0026aacute;n, G.-T., Hugo, J.-F., Carlos, B.-C., Arturo, H.-A., Edith, O.-T. \u0026amp; Claudia, \u0026Aacute;.-S. (2019) Integration of Isotopic (2H and 18O) and Geophysical Applications to Define a Groundwater Conceptual Model in Semiarid Regions. Water, 11, 488, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3390/w11030488\u003c/span\u003e\u003cspan address=\"10.3390/w11030488\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eArdana, P., Redana, W., Yekti, M. \u0026amp; Simpen, N. (2022) The Stable Isotopes Approach as Tracers to Investigate the Origin of Groundwater In The Unconfined Aquifer of Denpasar, Bali. Acta Montanistica Slovaca, 27, 968\u0026ndash;981.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBai, E., Guo, W., Zhang, D., Tan, Y., Guo, M. \u0026amp; Zhao, G. (2019) Using the magnetotelluric method for detecting aquifer failure characteristics under high-intensity mining of thick coal seams. Energies, 12, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3390/en12224397\u003c/span\u003e\u003cspan address=\"10.3390/en12224397\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBlasch, K. W. \u0026amp; Bryson, J. R. (2007) Distinguishing Sources of Groundwater Recharge by Using δ2H and δ18O. Ground Water, 45, 294\u0026ndash;308, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1111/j.1745-6584.2006.00289.x\u003c/span\u003e\u003cspan address=\"10.1111/j.1745-6584.2006.00289.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChave, A. D. \u0026amp; Jones, A. G. (2012) The Magnetotelluric Method: Theory and practice. \u003cem\u003eIn\u003c/em\u003e: Chave, A. D. \u0026amp; Jones, A. G. (eds) \u003cem\u003eThe Magnetotelluric Method: Theory and Practice\u003c/em\u003e Cambridge University Press, Cambridge, iii\u0026ndash;iii., doi: DOI: undefined.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen, H., Niu, Q., Mendieta, A., Bradford, J. \u0026amp; McNamara, J. (2023) Geophysics-Informed Hydrologic Modeling of a Mountain Headwater Catchment for Studying Hydrological Partitioning in the Critical Zone. Water Resources Research, 59, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1029/2023WR035280\u003c/span\u003e\u003cspan address=\"10.1029/2023WR035280\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eClark, I. (2015) \u003cem\u003eGroundwater Geochemistry and Isotopes\u003c/em\u003e CRC Press, Boca Raton pp.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDinas Pekerjaan Umum Provinsi Bali (2014) \u003cem\u003eLaporan Akhir Laporan Akhir Pekerjaan Peta Zonasi Pemanfaatan Air Tanah Provinsi Bali Tahun Anggaran 2014\u003c/em\u003e Denpasar pp.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEriksson, E. (1983) Guide Book on Nuclear Techniques in Hydrology. \u003cem\u003eIn\u003c/em\u003e: \u003cem\u003eGuide Book on Nuclear Techniques in Hydrology\u003c/em\u003e International Atomic Energy Agency, Vienna, 19\u0026ndash;33., doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1515/9783112517369-012\u003c/span\u003e\u003cspan address=\"10.1515/9783112517369-012\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFajar, M. H. M., Utama, U. W., Akbar, F. S., Hilyah, A., Pandu, J., Rochman, G. N. \u0026amp; Purwanto, M. S. (2019) Penentuan Daerah Imbuhan Dengan Metode Analisis Isotop Air Tanah di Desa Cottok, Kec. Kapongan Kabupaten Situbondo. Jurnal Geosaintek, 5, 31\u0026ndash;36.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGoldscheider, N. \u0026amp; Drew, D. (2007) \u003cem\u003eMethods in Karst Hydrogeology: IAH: International Contributions to Hydrogeology\u003c/em\u003e. 1st ed. CRC Press, London pp.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHamzah, U., Samsudin, A. R. \u0026amp; Malim, E. P. (2007) Groundwater investigation in Kuala Selangor using vertical electrical sounding (VES) surveys. Environmental Geology, 51, 1349\u0026ndash;1359, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s00254-006-0433-8\u003c/span\u003e\u003cspan address=\"10.1007/s00254-006-0433-8\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHendrayana, H., Nuha, A., Wiyatna, A. B., Muhammad, A. S. \u0026amp; Engineering, G. (2019) Hydrogen Isotope Study to Determine Groundwater Genesis in Mambal Spring, Bali, Indonesia Location. \u003cem\u003eIn\u003c/em\u003e: \u003cem\u003e11th Regional Conference on Geological and Geo-Resources Engineering \u0026lsquo;Innovations and Emerging Technologies for Responsible Mineral Resource Development\u0026rsquo;\u003c/em\u003e National Insitute of Geological Sciences, College of Science, University of the Philippines, Quezon City.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKendall, C. \u0026amp; Mcdonnell, J. J. (1998) \u003cem\u003eIsotope Tracers in Catchment Hydrology\u003c/em\u003e. 1st ed. Elsevier B.V., 839 pp.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKresic, N. \u0026amp; Stevanovic, Z. (2010) \u003cem\u003eGroundwater and Hydrology of Springs\u003c/em\u003e Butterworth-Heinemann, Burlington, 567 pp.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMarfia, A. M., Krishnamurthy, R. V, Atekwana, E. A. \u0026amp; Panton, W. F. (2004) Isotopic and Geochemical Evolution of Ground and Surface Waters in a Karst Dominated Geological Setting: a Case StudyFrom Belize, Central America. Applied Geochemistry, 19, 937\u0026ndash;946, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.apgeochem.2003.10.013\u003c/span\u003e\u003cspan address=\"10.1016/j.apgeochem.2003.10.013\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMaria, R., Satrio, Iskandarsyah, T. Y. W. M., Suganda, B. R., Delinom, R. M., Marganingrum, D., Purwoko, W., Sukmayadi, D. \u0026amp; Hendarmawan, H. (2021) Groundwater recharge area based on hydrochemical and environmental isotopes analysis in the south bandung volcanic area. Indonesian Journal of Chemistry, 21, 609\u0026ndash;625, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.22146/ijc.58633\u003c/span\u003e\u003cspan address=\"10.22146/ijc.58633\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMazor, E. (2004) \u003cem\u003eChemical and Isotopic Groundwater Hydrology\u003c/em\u003e. 3rd Editio. Marcel Dekker Inc., New York pp.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMudiana, W. \u0026amp; Setiadi, H. (2008) \u003cem\u003ePeta Sebaran Cekungan Air Tanah Pulau Bali\u003c/em\u003e Bandung pp.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMukherjee, A., Fryar, A. E. \u0026amp; Rowe, H. D. (2007) Regional-scale stable isotopic signatures of recharge and deep groundwater in the arsenic affected areas of West Bengal, India. Journal of Hydrology, 334, 151\u0026ndash;161, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.jhydrol.2006.10.004\u003c/span\u003e\u003cspan address=\"10.1016/j.jhydrol.2006.10.004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNgene, B. U., Nwafor, C. O., Bamigboye, G. O., Ogbiye, A. S., Ogundare, J. O. \u0026amp; Akpan, V. E. (2021) Assessment of water resources development and exploitation in Nigeria: A review of integrated water resources management approach. Heliyon, 7, e05955, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.heliyon.2021.e05955\u003c/span\u003e\u003cspan address=\"10.1016/j.heliyon.2021.e05955\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNuha, A., Hendrayana, H., Wiyatna, A. B., Putra, D. P. E. \u0026amp; Muhammad, A. S. (2020) Determination of Groundwater Recharge Area by Using Hydroisotope Technic of Sei Bingei Area and Surrounding Areas, Langkat Regency, North Sumatra. Journal of Applied Geology, 5, 13, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.22146/jag.51627\u003c/span\u003e\u003cspan address=\"10.22146/jag.51627\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePalano, M. (2022) Editorial for the Special Issue: \u0026ldquo;Ground Deformation Patterns Detection by InSAR and GNSS Techniques\u0026rdquo;. Remote Sensing, 14, 1104, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.3390/rs14051104\u003c/span\u003e\u003cspan address=\"10.3390/rs14051104\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePang, Z., Kong, Y., Li, J. \u0026amp; Tian, J. (2017) An Isotopic Geoindicator in the Hydrological Cycle. Procedia Earth and Planetary Science, 17, 534\u0026ndash;537, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.proeps.2016.12.135\u003c/span\u003e\u003cspan address=\"10.1016/j.proeps.2016.12.135\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePu, T., He, Y., Zhang, T., Wu, J., Zhu, G. \u0026amp; Chang, L. (2013) Isotopic and Geochemical Evolution of Ground and River Waters in a Karst Dominated Geological Setting: A Case Study From Lijiang Basin, South-Asia Monsoon Region. Applied Geochemistry, 33, 199\u0026ndash;212, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.apgeochem.2013.02.013\u003c/span\u003e\u003cspan address=\"10.1016/j.apgeochem.2013.02.013\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePurbo-Hadiwidjojo, M. M., Samodra, H. \u0026amp; Amin, T. C. (1998) \u003cem\u003ePeta Geologi Lembar Bali, Nusa Tenggara\u003c/em\u003e Bandung pp.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eS\u0026aacute;nchez-Murillo, R., Brooks, E. S., Elliot, W. J. \u0026amp; Boll, J. (2015) Isotope Hydrology and Baseflow Geochemistry in Natural and Human-Altered Watersheds in the Inland Pacific Northwest, USA. Isotopes in Environmental and Health Studies, 51, 231\u0026ndash;254, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1080/10256016.2015.1008468\u003c/span\u003e\u003cspan address=\"10.1080/10256016.2015.1008468\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSatrio, Prasetio, R., Hadian, M. S. D. \u0026amp; Syafri, I. (2017) Stable isotopes and hydrochemistry approach for determining the salinization pattern of shallow groundwater in alluvium deposit Semarang, Central Java. Indonesian Journal on Geoscience, 4, 1\u0026ndash;10, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.17014/ijog.4.1.1-10\u003c/span\u003e\u003cspan address=\"10.17014/ijog.4.1.1-10\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSetiawan, T. \u0026amp; Asgaf, N. M. A. (2016) Analisis Karakteristik Akuifer dan Zonasi Kuantitas Air Tanah di Dataran Kars Wonosari dan Sekitarnya, Kabupaten Gunungkidul, Provinsi Daerah Istimewa Yogyakarta. Jurnal Lingkungan dan Bencana Geologi, 7, 155\u0026ndash;167.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSimpson, F. \u0026amp; Bahr, K. (2005a) \u003cem\u003ePractical Magnetotellurics\u003c/em\u003e. Simpson, F. \u0026amp; Bahr, K. (eds) Cambridge University Press, Cambridge, 1\u0026ndash;14 pp., doi: DOI: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1017/CBO9780511614095.002\u003c/span\u003e\u003cspan address=\"10.1017/CBO9780511614095.002\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSimpson, F. \u0026amp; Bahr, K. (2005b) \u003cem\u003ePractical Magnetotellurics\u003c/em\u003e Cambridge University Press, Cambridge pp., doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1017/CBO9780511614095\u003c/span\u003e\u003cspan address=\"10.1017/CBO9780511614095\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSingh, M., Kumar, S., Kumar, B., Singh, S. \u0026amp; Singh, I. B. (2013) Investigation on the hydrodynamics of Ganga Alluvial Plain using environmental isotopes: a case study of the Gomati River Basin, Northern India. Hydrogeology Journal, 21, 687\u0026ndash;700, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s10040-013-0958-3\u003c/span\u003e\u003cspan address=\"10.1007/s10040-013-0958-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSudadi, P., Setiadi, H., Denny, B. R., Arief, S., Ruchijat, S. \u0026amp; Hadi, S. (1986) \u003cem\u003ePeta Hidrogeologi Lembar Pulau Bali\u003c/em\u003e Bandung pp.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSuryadi, A., Putra, D. B. E., Kausarian, H., Prayitno, B. \u0026amp; Fahlepi, R. (2018) Groundwater exploration using Vertical Electrical Sounding (VES) Method at Toro Jaya, Langgam, Riau. Journal of Geoscience, Engineering, Environment, and Technology, 3, 226, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.24273/jgeet.2018.3.4.2226\u003c/span\u003e\u003cspan address=\"10.24273/jgeet.2018.3.4.2226\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eToulier, A., Baud, B., de Montety, V., Lachassagne, P., Leonardi, V., Pistre, S., Dautria, J.-M., Hendrayana, H., Miftakhul Fajar, M. H., Satrya Muhammad, A., Beon, O. \u0026amp; Jourde, H. (2019) Multidisciplinary study with quantitative analysis of isotopic data for the assessment of recharge and functioning of volcanic aquifers: Case of Bromo-Tengger volcano, Indonesia. Journal of Hydrology: Regional Studies, 26, 100634, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ejrh.2019.100634\u003c/span\u003e\u003cspan address=\"10.1016/j.ejrh.2019.100634\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWijatna, A. B., Sudarmadji, Sunarno \u0026amp; Hendrayana, H. (2013) Studi Variabilitas Isotop Airhujan Sebagai Fungsi Elevasi untuk Mendapatkan Merapi Meteoric Water Line (MMWL). Forum Teknik, 35, 50\u0026ndash;57.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYamashita, M. \u0026amp; Ii, H. (2016) Estimation of evaporation rate of surface water using hydrogen and oxygen isotopic ratios. International Journal of GEOMATE, 11, 2659\u0026ndash;2664, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.21660/2016.26.5295\u003c/span\u003e\u003cspan address=\"10.21660/2016.26.5295\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZamrsky, D., Oude Essink, G. H. P. \u0026amp; Bierkens, M. F. P. (2024) Global Impact of Sea Level Rise on Coastal Fresh Groundwater Resources. Earth\u0026rsquo;s Future, 12, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1029/2023EF003581\u003c/span\u003e\u003cspan address=\"10.1029/2023EF003581\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhou, R. X., Wang, J., Tang, C. J., Zhang, Y. P., Chen, X. A., Li, X., Shi, Y. Y., Wang, L., Xiao, H. B. \u0026amp; Shi, Z. H. (2023) Identifying soil water movement and water sources of subsurface flow at a hillslope using stable isotope technique. Agriculture, Ecosystems \u0026amp; Environment, 343, 108286, doi: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.agee.2022.108286\u003c/span\u003e\u003cspan address=\"10.1016/j.agee.2022.108286\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Spring, Recharge area, Isotopes, Vertical electrical sounding, Audio magneto telluric","lastPublishedDoi":"10.21203/rs.3.rs-4279145/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4279145/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIdentifying spring recharge areas is essential for water resource conservation. This study aimed to determine the recharge area of Ababi Spring, Indonesia, using stable isotope, vertical electrical sounding (VES), and audio magnetotelluric (AMT) methods. Rainwater and spring water were sampled at 211\u0026ndash;978 m locations above sea level. Hydrogen and oxygen isotope ratios revealed that spring water originated from a higher elevation source. The relationship between oxygen isotope composition and elevation was used to estimate the spring recharge elevation as 2,118-2,137 m above sea level. VES and AMT methods generated geoelectrical profiles depicting subsurface water flow from recharge to discharge zones, confirming the elevated recharge area. Additional isotope analysis of 1,514 m altitude rainwater supported the prediction model. This multidisciplinary approach combines hydrochemical and geophysical techniques to enable more reliable delineation of groundwater recharge areas than single methods. Determining the Ababi Spring recharge zone facilitates targeted conservation efforts for this vital water resource. Further work should investigate geochemical evolution along subsurface flow paths.\u003c/p\u003e","manuscriptTitle":"Identifying spring recharge areas using stable isotope and geophysical methods: A case study of the Ababi Mountain Region, Bali, Indonesia","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-29 16:36:05","doi":"10.21203/rs.3.rs-4279145/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"5f6c3e85-c21e-414a-8b7e-bcc472ac9e27","owner":[],"postedDate":"April 29th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-05-19T11:23:33+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-29 16:36:05","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4279145","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4279145","identity":"rs-4279145","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}