Evidence for high-elevation salar recharge and interbasin groundwater flow in the Western Cordillera of the Peruvian Andes

Improving our understanding of hydrogeological processes on the western flank of the central Andes is critical to communities living in this arid region. Groundwater emerging as springs at low elevations provides water for drinking, agriculture, and baseflow. However, the high-elevation sources of recharge and groundwater flowpaths that convey groundwater to lower elevations where the springs emerge remain poorly quantified in the volcanic mountain terrain of 20 southern Peru. In this study, we identified recharge zones and groundwater flowpaths supporting springs east of the city of Arequipa and the potential for recharge within the high-elevation closed-basin Lagunas Salinas salar. We used general chemistry and isotopic tracers (δ18O, δ2H, and 3H) in springs, surface waters (rivers and the salar), and precipitation (rain and snow) sampled from March 2019 through February 2020 to investigate these processes. We obtained monthly samples from six springs, bimonthly samples from four rivers, and various samples from high-elevation springs during the dry season. The 25 monthly isotopic composition of spring water was invariable seasonally in this study and compared to published values from a decade prior, suggesting that the source of recharge and groundwater flowpaths that support springflow are relatively stable with time. The chemistry of springs in the lowand mid-elevations (2500 to 2900 masl) point towards a mix of recharge from the salar basin (4300 masl) and mountain-block recharge (MBR) in or above a queñuales forest ecosystem at ~4000 masl on the adjacent Pichu Pichu volcano. Springs that clustered along the Río Andamayo, including those at 2900 masl, had higher 30 chloride concentrations indicating higher proportions of interbasin groundwater flow from the salar basin likely facilitated by a high degree of faulting along the Río Andamayo valley compared to springs further away from that fault network. A separate groundwater flow path was identified by higher sulfate concentrations (and lower Cl-/SO4-2 ratios) within the Pichu Pichu volcanic mountain range separating the city from the salar. We conclude that the salar basin is not a hydrologic dead-end. Instead, it is a local topographic low where surface runoff during the wet season, groundwater from springs, and subsurface 35


Introduction
Predicted climate change in the tropical Andes includes increases in temperature and evapotranspiration and changes in precipitation patterns (Urrutia and Vuille, 2009;Somers et al., 2019). A ~10-30% reduction in precipitation is projected for the western Andeas in the coming century (Minvielle and Garreaud, 2011;Neukom et al., 2015). These changes are projected to have a negative impact on the long-term sustainability of critical groundwater resources in southern Peru (Vuille et al., 45 2018). High-elevation zones of groundwater recharge in the Andes are extremely sensitive to the interplay between evapotranspiration and precipitation due to climate and anthropogenic land-use change altering vegetative land cover, energy balance, and water balance. Recharge occurring in the mountain block at high elevations is called mountain-block recharge (MBR; see Manning and Solomon, 2003;Wilson and Guan, 2004;Wahi et al., 2008;Ajami et al., 2011;Bresciani et al., 2018).
If the amount of precipitation decreases in high-elevation recharge zones, then the amount of effective precipitation 50 (precipitation minus evapotranspiration) potentially available for MBR likewise decreases (Goulden et al., 2012;Goulden and Bales, 2014). In addition, if the land cover changes in the recharge zone (e.g., changes in vegetation type, density, health and/or movement of the treeline), then the MBR will also change. While the effects of MBR reduction may not be immediately felt in the region, they are not inconsequential. Groundwater flow within the mountain block impacts spring flow, headwater streams that originate in the mountain block and subsequently flow across the mountain front, and groundwater wells often 55 located at lower elevations along the mountain front or in adjacent valleys. The importance of MBR on groundwater resources in the Andes and how they might respond to changing precipitation and temperature and melting glaciers are poorly understood (Somers et al., 2018;Somers et al., 2019).
Springs emerging within and down-gradient from the mountain block are important in the high, arid Andes of Peru for a variety 60 of reasons. They provide a source of potable water and can be used for irrigation and recreation, and some have ecological or religious significance (Stensrud, 2019;Sedapar, 2018;Gerencia Regional de Agricultura de Arequipa, 2015). Communities at lower elevations of the western Andes receive very low annual precipitation and rely on surface runoff and groundwater originating from higher elevations (Urrutia and Vuille, 2009). Consequently, identifying groundwater recharge zones and source areas for springs can help us better understand the potential impact of climate change to water resources and better 65 inform water management plans including the protection of perennial springs and their high-elevation recharge zones. This is complicated by the presence of closed-basin salars at high elevations in southern Peru (Juvigné et al., 1997). Some of the runoff that occurs during the wet season is captured by these basins and does not contribute (at least directly) to surface runoff across the mountain front. Furthermore, these basins are not usually considered a recharge zone (Peña, 2018); however, these salars are local topographic lows and are likely points of groundwater discharge from the surrounding mountains. 70 There are more than one hundred salars in topographic depressions in the high mountainous arid region of the Central Andes (Warren, 2016). These salars occur within a tectonically active region with largely interior (endorheic) drainage from the Andean highland plateaus of Chile, Bolivia, Argentina, and southern Peru. Endorheic basin salars form because the topography of the region favors water accumulation in depressions, and evaporation rates are very high (Warren, 2016). Salars are generally 75 considered closed basins, but not all salars are terminal lakes (Warren, 2016;Risacher et al., 2003). This means that salar brines can infiltrate, be transported elsewhere, and/or mix with meteoric waters (Warren, 2016;Risacher et al., 2003). By using the ratio of the total mass of chloride (assumed to be a conservative tracer and assuming insignificant wind erosion) in the brine lakes to the annual input flux to estimate the tracer's residence time, Risacher et al. (2003) determined that the residence times of Clin Chilean brine lakes were short (few to hundreds of years) in a flow-through steady-state condition. This means 80 that most dissolved salts entering salars in this region are lost by leakage through bottom sediments and reenter the hydrologic system (Risacher et al., 2003), which suggests that salars may play an important role as sources of groundwater recharge despite differences in buoyancies between the brines and fresh-water recharge. In general, the potential for high-elevation closed-basin salars, which are commonly thought to represent the hydrological dead-end of surface flowpaths, to contribute groundwater recharge to support springs in the central Andes remains uncertain. This begs the question; are all high-elevation 85 salars simply evaporation pans or can leakage beneath the salar contribute to groundwater recharge?
Hydrogeological studies have been conducted in salars and groundwaters of Chile to understand groundwater recharge processes, sources of spring flow, the hydrogeologic connectivity of high-elevation mountains and salar basins to the downvalley aquifers and residence times of groundwaters in these basins (Boutt et al., 2016;Jayne et al., 2016, Scheiling et al., 90 2017, Herrera et al., 2016Fritz et al., 1981). Groundwater stable isotopes depleted in deuterium ( 2 H) and oxygen-18 ( 18 O) suggest that the main source of aquifer recharge is precipitation at high elevations (~4000 m.a.s.l) of the Altiplano and Andean mountain ridge (Jayne et al. 2016, Scheiling et al., 2017. Early stable isotope research proposed that groundwater recharge to the Pampa del Tamarugal (~1000 m.a.s.l.), which is the most economically important aquifer in the Atacama Desert, occurs in the nearby Precordillera Altos de Pica (~3500 m m.a.s.l.; Fritz et al., 1981). Subsequent studies pointed to recharge further 95 inland at the Salar de Huasco basin (~3700 m.a.s.l.) through deep fissures that connect the salt-crusted salar to springs in the town of Pica and the Pampa de Tamarugal (Magaritz et al. 1989(Magaritz et al. , 1990. However, recent research rejected the possible influence of the high-elevation Salar de Huasco to groundwater recharge of lower elevation springs based on isotopic characterization (Uribe et al., 2015) and geothermometer inference (Scheiling et al., 2017). Nearby, Herrera et al. (2016) suggest that there may be a small amount of recharge from Laguna Tuyajto (4010 m.a.s.l.) in Chile to the underlying Salar de 100 Aguas Calientes-3 basin (3939 m.a.s.l.). Furthermore, they state that, despite differences in buoyancy between saline brines and fresh groundwater, some proportion of the saline water from Laguna Tuyaito likely mixes and becomes incorporated with regional groundwater flow. Tritium ( 3 H) offers insight into these mixing processes and can provide valuable information on residence times of groundwater that stable isotopes typically cannot. For example, Moran et al. (2019) used tritium ( 3 H) to age-date waters across the Salar de Atacama in Chile from the surrounding mountains to the basin lagoons and found evidence 105 of 3 H dead groundwater inferred to be older than 60 years. Their data indicate that groundwater discharge to the Salar de Atacama is interbasin flow of pre-bomb recharge from other internally-drained basins at higher elevations.
The salars and mountain-groundwater systems of Peru have received much less attention compared to Chile. Few hydrogeological studies have quantified groundwater recharge processes in southern Peru. Arequipa (2300 m.a.s.l.) is Peru's 110 second largest city (with a population exceeding 1 million), and it is situated near a high-elevation (4300 m.a.s.l.) closed-basin salar, Laguna Salinas. Local research conducted on the source of springs east of the city of Arequipa by the Peruvian Agency INGEMMET ("Instituto Geologico, Minero y Metalurgico") indicates that the zone of groundwater recharge is precipitation on a nearby high-elevation volcano called Pichu Pichu (Peña, 2018). However, the potential influence of the Lagunas Salinas basin and the salar itself as a recharge source for the lower elevation springs has not been thoroughly investigated. Due to the 115 importance of groundwater in southern Peru, , it is essential to study the hydrogeological behavior of the basins throughout the region. The objectives of this study are: 1) to identify sources of recharge and 2) quantify groundwater flowpaths supporting springs near the city of Arequipa using natural geochemical and isotopic tracers measured in springs, surface waters (rivers and salar), and precipitation (rain and snow). We assessed the contribution of high-elevation precipitation or salar recharge using a combination of stable isotopes (d 18 O and d 2 H) and geochemical tracers. Tritium ( 3 H) was used as a reconnaissance tool 120 on a subset of springs to provide insight into the ranges of residence times for these springs. Specifically, we address the question: is the Laguna Salinas a source of recharge for the deeper groundwater system that supports low-elevation springs in the Arequipa region?

Study area
Our study is in the Central Andes of southwestern Peru in the department of Arequipa between the Andean Western Cordillera 125 and the coastal belt at 16⁰20'S latitude and 71⁰30'W longitude (Figure 1). In this section we provide context for the study and a description of the potential geologic controls on the hydrology of the region.

Water uses
The Río Chili, which flows through the city, and La Bedoya spring to the east are the two main sources of drinking water for the metropolitan area of Arequipa (Sedapar, 2018). Commercial crop production and self-consumption rely on these water 130 resources in addition to large-scale water diversion projects from the neighbouring Majes watershed (MINCETUR, 2017; Gerencia Regional de Agricultura de Arequipa, 2015). Water-intensive mining activities also occur throughout Arequipa, including the Cerro Verde mine just south of the city (MINCETUR, 2017). According to census data from 2007 to 2017, population growth in arid coastal areas of Peru increased 1.3% annually and the capital city population increased 2.3% annually (from 806,782 to 1,008,290 people from 2007 to 2017) (INEI, 2018). Continued population growth and a growing agricultural 135 sector stress water resources in southern Peru.

Climate
The western central Andes has experienced an arid to semi-arid climate since the modern Andes were uplifted in the Middle Miocene, forming a barrier to easterly winds (Warren, 2016). In the early to middle Pleistocene, several glaciations occurred in this region; however, most Andean glaciers have receded since the mid-19 th century (Seltzer, 1990;Ehlers et al., 2011).
Today, the western part of the Central Andes is characterized by a strong annual cycle of precipitation consisting of a very dry 145 winter (June to August) and a wet summer monsoon season (November to April) bringing precipitation from the Amazon with large interannual variability (Garreaud, 2009;Urrutia and Vuille, 2009;Imfeld et al., 2021). The Pichu Pichu volcano commonly accumulates snow during the summer wet season. Average annual precipitation is higher (400-600 mm at elevations above 4000 m.a.s.l.) compared with lower elevations in the department of Arequipa (~100 mm) (Moraes et al., 2019). Annual average temperatures are cooler at higher elevations and warmer at lower elevations near the coast, except for near large rivers 150 such as the Río Majes and Río Tambo (Moraes et al., 2019). Figures S1 and S2 show the monthly mean precipitation and temperature climatology at 3 elevations within our study region.
There are two meteorological stations operated by the Peruvian Servicio Nacional del Meteorolgía e Hidrología del Perú (SENAMHI) in our study watershed, located in the districts of Chiguata and Salinas Huito (near Laguna Salinas) (Senamhi, 155 2020). Annual 2018 precipitation was 140 mm for Chiguata (2902 m.a.s.l.) and 350 mm for Salinas Huito (4349 m.a.s.l.). The 2018 annual maximum temperature for Chiguata and Salinas Huito were 20.3⁰C and 12.7⁰C, respectively, while minimum temperatures were 5.9⁰C and -4.7⁰C. Data for 2019 had many gaps and quality control issues at Salinas Huito so it is not reported here.

Geologic description
Our study focuses on the Chili watershed which can be divided in three main geomorphologic landforms largely shaped by tectonic and volcanic processes: 1) the Arequipa depression, 2) the Western Cordillera which comprises the Grupo Barroso and cluster of volcanoes, and 3) the highland hills and depressions surrounding Laguna Salinas (Peña, 2018; Thouret et al., 2001). 165 The complex geology of the region includes rock units of high and low permeability and faulting that influence groundwater 175 flowpaths. Low permeability basement rock of the Arequipa massif (Jenks, 1948;Peña, 2018) limits hydrologic conductivity at depth and creates a barrier to groundwater flow (Guevara, 1965) and possibly deep circulation. This Pre-Cambrian feldspathic Charcani gneiss is exposed in small outcrops along river channels of the districts of Mollebaya and Yarabamba.
Thick volcanic deposits and carbonate formations associated with extensional processes during back-arc formation of the Arequipa-Tarapaca Basin overlie the basement Charcani gneiss (Sempere et al., 2002;Vicente, 2006). Thick sediments of the 180 Mesozoic Socosani formation with sequences of limestones interbedded with black shales and sandstone are ca. 80 m thick in Arequipa (Jenks, 1948). Detrital clastic sediments of the Grupo Yura contain sequences of sandstone interbedded with thin layers of shales and limonites. The Grupo Yura is overlain by younger volcanic deposits from the late Miocene to Pleistocene from the Grupo Barroso, which is characterized by porphyritic andesite lavas from volcanoes Pichu Pichu and Misti. Local confined and unconfined aquifers have previously been identified within permeable units interbedded between baked contacts 185 within the Grupo Barroso (Peña, 2018). Fluvioglacial fill deposits on the slopes of Pichu Pichu Volcano lay beneath more recent pyroclastic and clastic materials (Thouret et al., 2001). A landslide of pyroclastic deposits ca. 400 m thick outcrop along the Río Andamayo gorge with a pseudotachylyte basal contact with the underlying ignimbrite may limit deep circulation in the Characato area (Legros et al., 2000). Springs in our Chiguata study site lay above paleolake deposits comprised of high permeability sandstones and thin units of low permeability stratified diatomite and clay (Garcia et al., 2016). Finally,alluvial 190 and fluvial deposits consisting of mainly gravel, sand, silt, and poorly consolidated conglomerates are distributed in the banks of the Ríos Chili, Andamayo, and Yarabamba.
Faults are common throughout the study area ( Figure 2). Some of the faults are associated with volcanic activity (ring-fracture faults and normal faults) and others are associated with strike-slip plate motion. These faults are likely hydrogeologically 195 important because the fractures associated with the faults can either enhance groundwater flow or act as barriers directing groundwater to the surface. The Western Cordillera volcanic complexes (Misti and Pichu Pichu) are aligned along a strike-slip fault that trends from NW to SE (Mering et al., 1996;Thouret et al., 2001). While many faults have been mapped in this region ( Figure 2, Thouret et al., 2001;Lebti et al., 2006;Bernard et al., 2019), the normal faults (NW to SE direction) in the district of Chiguata are most relevant to our study (Benavente et al., 2017, Thouret et al., 2001. The Río Andamayo flows along a 200 fault separating the older Pichu Pichu mountain block from the uplift associated with Misti ( Figure 2).
In the highlands, the Laguna Salinas closed-basin salar likely formed during the creation of the late Miocene to early Quaternary volcanic range, which includes the Pichu Pichu, Misti, Ubinas, and Chachani volcanoes (Lebti et al., 2006); and following an eruption of the Pichu Pichu volcano 6.7 Ma ago (Kaneoka and Guevara 1984;personal communication with Jean-205 Claude Thouret, 2020). The salar covers ~142 km 2 (Garrett, 1998) and floods to an average depth of 50 cm during the rainy season from December to March, and then nearly completely dries during the long dry season. Springs from higher elevations in the surrounding mountains contribute water to the salar basin, but there is no surface outflow draining it. Water loss is entirely evaporation and potentially groundwater recharge. Economically important evaporite minerals form in the salar during the dry season. These minerals, ulexite, halite, Glauber salt, and thenardite, are found at the crust of the salar and with depth 210 in the lacustrine deposits (Muessig, 1958;Garrett, 1998). The lacustrine deposits consist of layers of halite and thenardite (Na2SO4) at the surface (5-15 cm), followed by a thin white volcanic ash layer (< 15 cm), various mud layers containing ulexite (NaCaB5O9*8H2O; ~ 1.5-1.8 m), and the main ulexite bed occurs between 0.25 to 1.3 m in the lacustrine sediments. Inyoite (Ca2B6O11*13H2O) is also present beneath the ulexite bed along the eastern side of the salar near the Tusca Hot Spring (<15 cm; Muessig, 1958;Garrett, 1998). 215

Watershed description and sampling locations
The Río Chili watershed drainage is part of the Quilca-Vitor-Chili River basin, extending from the Andean Altiplano to sea level at the Pacific coast. Our research was conducted in the districts of Characato (~2500 m.a.s.l.), Chiguata (~3000-3500 220 m.a.s.l.) and the high-elevation closed-basin salar, Laguna Salinas (~4300 m.a.s.l.) 80 km east of the city of Arequipa ( Table 1 lists coordinates, elevation, names, and IDs of water samples collected in this study. We sampled a total of six low- (MNE and MCU, 4657 -4888 m.a.s.l.). Snow was collected at the surface and at ~10 cm depth placed in ziploc bags and allowed to melt at room temperature before being transferred to 1L bottles. We also sampled three springs (MSI, PUQ, and QUE) in the high elevation queñuales forest (3770 -4052 m.a.s.l.), in May and October 2019. Pluviometers installed in Characato (2300 m.a.s.l.) near the La Pampilla SENAHMI station and in Chiguata (2969 m.a.s.l.) as part of a complementary 250 research effort were used to collect daily rainwater during the wet season from January to March (Welp et al., in preparation).

Water sampling
The rest of the year there is almost no precipitation ( Fig S1). Rain gauges were emptied each morning to minimize evaporation.
Spring, river, and salar water samples were collected using a collection tube below the surface of the river or the spring emergence connected to a hand-pump and filtered using a 0.45 µm membrane into 25-mL (with poly-seal caps) and 250-mL plastic bottles for stable isotope and general chemistry analysis respectively. If the spring emergence was not accessible, the 255 closest possible pool of flowing water was sampled. Additional 1-L samples for tritium ( 3 H) analyses were collected at 4 sites (INK, UBI, OJO, and BED) in September 2019, and Pichu Pichu snow (PPI) from May 2019, and Arequipa precipitation (MID) from February 2020. All plastic bottles were tightly closed and sealed with electrical tape to prevent water leakage and reduce evaporation. Water temperature (°C) and pH were measured in-situ at all sites using a handheld Oakton meter (AO-35423-01). Electrical conductivity (EC) was measured in the field using a YSI Professional Plus (Quatro) multi-parameter 260 probe. The YSI probe calculates 1) specific conductivity (SpC, µS cm -1 ) from: SpC = EC * 1.91; where 1.91 is the temperature coefficient at 25°C, and 2) total dissolved solids (TDS, ppm) from: TDS = EC * 0.65.. (Table S1). Both instruments were calibrated daily and recalibrated at different altitudes. Table 1. Location, sample ID, elevation, and months sampled of springs, snow, and surface waters. These sites are mapped in Figure  2. *Indicates this site was analyzed for 3 H. Research, San Jose, California USA, model T-LWIA-45-EP). The first 4 of 10 total injections were excluded due to memory effects (Penna et al., 2012) and the last six injections were averaged for the reported value. Data is reported relative to the international VSMOW-SLAP standard scale (Vienna Standard Mean Ocean Water-Standard Light Antarctic Precipitation), with an analytical error of <0.2‰ and <1.0‰ for δ 18 O and δ 2 H, respectively. 275

Sample Group/Location
Tritium ( 3 H) was analyzed to identify the mixing relationships, sources of recharge, and the presence/absence of modern recharge. The atmospheric 3 H breakthrough associated with nuclear weapons testing in the 1950s and 1960s observed in South America and the Southern Hemisphere was not similar to that observed in North America and the Northern Hemisphere. For example, the tritium breakthrough peaked at approximately 60 TU in Cuiabá, Brazil in 1965 and many equatorial monitoring 280 stations measured breakthroughs less than 40 TU (Albero & Panarello, 1981). In comparison, the atmospheric breakthrough was much higher in the northern hemisphere; the tritium breakthrough in Miami, FL, USA peaked at 384 TU in 1964 while the peak was over 3800 TU in Chicago, IL, USA in 1964. Thus, it's not unusual to find tritium-dead groundwater in the Southern Hemisphere since the 3 H in recharge occurring during the bomb-pulse era has largely decayed back to pre-bomb levels. Regardless, 3 H measurements in springs and groundwater from salars may still be useful as a reconnaissance tool for 285 future age-dating especially if modern samples of precipitation and other appropriate endmembers are characterized for comparison.
Samples of one litre were collected for 3 H in the field, stored in high density polyethylene bottles with leak free caps and were not exposed to indoor air. Samples PPI, OJO, BED, INK, and UBI, as well as a one-time 1L sample of rain within the city of 290 Arequipa during Feb 2020, were analyzed for 3 H at the University of Miami, Tritium Lab. Water samples were distilled, enriched via an electrolyzed water bath for 10 to14 days, reduced over hot magnesium metal, and transferred to the counter for 6 to 20 hours. Backgrounds are set by comparison to tritium dead petroleum and deep Florida Aquifer waters. Efficiency is determined by preparation of the NIST SRM#4926 standard water (Östlund et al., 1987). The reported accuracy and precision for ultralow activity electrolytic enrichment through volume reduction is 0.1 TU. 295

Chemical analysis
Cation (Ca 2+ , Mg 2+ , Na + , and K + ) and anion (Cl -, Br -, SO4 2-, and HCO3 -) analyses were conducted by the New Mexico Bureau of Geology & Mineral Resources. Cations were measured by inductively coupled plasma optical emission spectrometry (ICP-OES, PerkinElmer Optima 5300 DV) following EPA Method 200.7 (USEPA, 1994). Anions were measured by ion chromatography (IC-Dionex ICS-5000) following EPA Method 300.0 (USEPA, 1993). Precision for major ions varied by ion 300 but was < 6 mg/L for everything reported here. Additional precision details can be found in Table S1. Boron and Lithium concentrations were determined using ICP-OES at Purdue University (iCAP 7400, Thermo Scientific, China) with dual plasma view, equipped with Qtegra ISDS software. Concentration standards for both ranged from 2 to 2,000 ppb and had correlation coefficients of 0.9959 for B and 0.9948 for Li. The limits of detection for B and Li were 1.1 and 0.1 ppb and the limits of quantification were 3.6 and 0.2 ppb, respectively. The accuracies for both elements were above 90%. Values above 2,000 ppb 305 were reported as above the maximum calibration range.

Isotopic composition of precipitation, surface, springs and salar water
The local meteoric water line (LMWL) calculated from daily rain collections in 2019-2020 was δ 2 H = 8.0 δ 18 O + 10.9‰. The monthly isotopic composition of Characato and Chiguata springs was largely invariable over time (Table S1). The monthly 310 stable isotopic composition of the springs in the district of Characato ranged from -8.7 to -10.1‰ for δ 18 O and -58 to -68‰ for δ 2 H (Figures 3) with mean values reported in Table 2. Springs in the district of Chiguata have more depleted isotopic compositions with monthly values ranging from 11.6 to -12.9‰ for δ 18 O and -85 to -97‰ for δ 2 H ( Figure 3 and Table S1) with mean values reported in Table 2 (Table S1).
Note that high elevation precipitation (>3000 m.a.s.l.) other than Pichu Pichu snow (PPI) was not sampled in this study. 320 Samples from Laguna Salinas surface water (LSA) obtained in the dry season (October 2019) had a highly enriched isotopic composition, while LSA sampled during the wet season (April 2019) had an isotopic composition of -16.3‰ δ 18 O and -122‰ δ 2 H, similar to springs in that area (Figure 3).
The measured 3 H activities of modern rainfall from the city of Arequipa and in snow from Pichu Pichu summit were 1.4 TU 325 and 2.2 TU, respectively. In contrast, the tritium activities of the springs INK and UBI in the Lagunas Salinas basin as well as OJO in Characato and BED in Chiguata were considered 3 H dead since lab reported values were at or below the detection limit of 0.1 TU. In contrast to nearly isotopically-constant spring waters, most rivers were more variable (Figure 4). The exception is the Río Characato (RCH), which only varied by 1‰ in δ 2 H during our sampling dates. The Río Socabaya (SOC) and the Río Andamayo sampled at Chiguata (ATA) showed more depleted isotopic values in February 2020. The isotopic composition of the Río Mollebaya (MOL and MOY) was more enriched than most rivers except the Río Characato, and also showed slightly more enriched isotopic composition during June and September compared to other months. The isotopic values of the Río Andamayo 350 sampling site at Chiguata in the dry season are comparable to the composition of springs sampled in Chiguata (BED and BAD).

Hydrochemical facies and processes
Most chemistry of springs in our study region fall on a mixing line between sodium chloride (NaCl) and calcium sulfate (CaSO4) water types ( Figure 5). NaCl type waters include Laguna Salinas surface water, three springs near Laguna Salinas 365 (UBI, MOQ, and INK), and springs in the district of Chiguata (BED and BAD). Pichu Pichu snow, one Pichu Pichu spring (MCU) and two Characato springs (OJO and ANA) plot towards the CaSO4 quadrant, while the Characato springs that are geographically closer to the Río Andamayo (SAN and YUM) plot in the middle of this inferred mixing line. Since two springs in Characato had greater NaCl percentage (SAN and YUM) than the other two springs (OJO and ANA), we classified samples from Characato into two groups: NaCl and SO4 2springs. 370

Figure 5: Piper diagram of all groundwater samples, Lagunas Salinas surface water, and snow sample in this study. Quadrant I represents calcium-bicarbonate waters, quadrant II represents sodium-chloride waters, quadrant III represents sodiumbicarbonate waters, and quadrant IV represents calcium-sulfate waters.
Gibbs diagrams are commonly used to identify relative controls of three processes on water chemistry: precipitation dominance (rainfall), evaporation dominance, and rock-weathering processes. Marandi and Shand (2018) caution that Gibbs diagrams are not always sufficient when interpreting the processes that affect the geochemistry of groundwater. For example, mixing with saline connate groundwater can pull samples to the evaporation influence region of the plot. In our study area there are no 380 ancient marine deposits, so we reject this complication. The Gibbs diagram shows that the low-elevation spring samples which appear to recieve some mixture of high-elevation high-salinity recharge fall along a proposed mixing line with this subspace.
In addition, Marandi and Shand (2018) specifically state that waters that plot in the upper right corner of the diagram are affected by the presence of surface salts. This is the exact condition which we propose is happening in the connection between saline recharge from the salar and the Chiguata springs. Saline recharge would plot in the evaporative enrichment field where 385 the Laguna Salinas surface waters (LSA) plot. This saline recharge then mixes with fresh groundwater in the mountain block that was recharged by high-elevation snow and/or rain. Thus, Chiguata springs plot between the fields for evaporative enrichment and precipitation dominance. In comparison, springs such as the queñuales forest springs and Pichu Pichu springs, which are supported by high-elevation recharge from snowmelt and/or rain, plot near the precipitation dominance field for anions and rock-weathering for cations. The placement of these endmembers in these fields of the Gibbs diagrams make 390 physical sense. Thus, the Gibbs diagrams appear robust for springs in Characato and Chiguata and for springs and surface waters near Laguna Salinas. The Gibbs diagrams for the major ion compositions of our springs indicate that water chemistry of Characato and Chiguata springs is controlled by water-rock interactions (Figure 6a, b). Chiguata springs plot at the distal end of the rock dominance region and closer to the evaporation dominance region than the Characato springs. Two springs near Laguna Salinas (UBI and MOQ) also fall in the evaporation dominance area. 395

415
The relationship between Cland SO4 2shows two trends: one for Chiguata (BED and BAD) and Characato NaCl (YUM and SAN) springs with higher Cllocated along the Río Andamayo fault system, and another one for Characato SO4 2springs with lower Cllocated in a secondary cluster of shorter faults (Figures 2 and 8). This relationship between Cland SO4 2highlights mixing between recharge from Laguna Salinas (high in Cland SO4 2-) and MBR from precipitation occurring on the Pichu 420 Pichu volcano (low in Cland SO4 2-). Additionally, the mixing lines ( Figure 8

Discussion
Here we discuss evidence of the recharge elevations and groundwater flow paths connecting the Lagunas Salinas salar and the Pichu Pichu volcano to the Chiguta and Characato springs. 435

Groundwater recharge elevations inferred from stable isotopes
In most orographic precipitation studies along mountain ranges, the stable water isotopic composition of precipitation becomes progressively more depleted at higher elevations (Dansgaard et al 1964; Clark and Fritz et al., 1997;Różański et al., 1993).
This relationship allows the elevation of spring recharge to be estimated using stable water isotopes. Our observations show that high-elevation snow, springs, and wet-season salar surface waters are isotopically depleted compared to lower elevations 440 ( Figure 3b). However, we observed very little difference in the d 18 O and d 2 H between springs at 2,533 m in Characato and springs at 3,944 m in the queñuales forest, despite the large elevation difference. As observed in Figure 3a, the springs sampled at the queñuales forest fall very near to the meteoric water line, which suggests that there is not isotopic enrichment of these springs caused by enhanced local evaporation in this ecosystem. Given the nearly identical isotopic values, we believe it is likely that springs in the queñuales forest and Characato share a common recharge elevation of ~4,000 m or above. We can 445 not conclusively rule out Characto spring recharge by Characato precipitation because the mean 2019 rain isotope value was very similar to the spring values, but the mean 2020 rain isotope values show that many years of observations would be needed to make a meaningful comparison with local rain. The 3 H-dead waters in Characato also point to high elevation recharge instead of local. Springs from the Chiguata district have isotopic values that fall in between depleted values of Laguna Salinas springs and Pichu Pichu snow, and relatively enriched values of the queñuales forest springs (Figure 3b); which suggests that 450 Chiguata springs receive a mix of water from higher elevations including possible contributions from snowmelt, mediumelevation queñuales forest springs (presumably fed by rainfall near that elevation), and recharge from the Laguna Salinas in the wet season.
Regionally, the isotopic lapse rate of surface waters in the Western Cordillera is estimated to be -10‰ d 18 O per km (Bershaw 455 et al., 2016), which is much larger than observed in this study based on limited precipitation collections (~-3‰ d 18 O per km from PPI and PRP-Characato data). The factors controlling the isotopic values of precipitation in the Western Cordillera of the Andes are poorly understood, partly due to lack of data (Valdivielso et al., 2020). Aravena et al. (1999)  high-elevation springs on Tacune cannot be explained otherwise. Another explanation for the depleted isotopic composition of Laguna Salinas springs is paleorecharge from the Last Glacial Maximum (LGM) glacial meltwater stored in the basin. We do not have data to test this conceptual model, but glaciers were present in the vicinity of the Laguna Salinas basin during the LGM (Seltzer, 1990;Juvigné et al., 1997). Additional sampling and dating of springs and wells in the area are necessary to thoroughly test LGM influence. 485 The long-term stability of the Characato springs' isotopic values within our study period and a sampling from a decade ago indicates that they are supported by a stable source of recharge that is nonresponsive to the temporal short-term variability in rain events within a wet season or interannually. Three of our springs (YUM, OJO, and BED) were also sampled in 2009 by Sulca et al. (2010) and the stable isotopic results obtained in their study were nearly identical to ours 10 years later (Table 2). 490 The 3 H values of OJO and BED indicate the groundwaters are older than 60 years as well. However, a comparison of spring discharge measurements made once in 1977 and once in 2016 reveals that the discharge from some springs has decreased over this 40-year interval. Spring discharge of Yumina, Ojo de Characato and La Bedoya was 255, 216, and206 L/s, respectively, in 1977 (Diaz, 1978);and215, 206, and114 L/s, respectively, in 2016 (Peña Laureano, 2018), reflecting decreases of 16%, 5%, and 45% respectively. Differences in discharge may also be due to the variability in time-of-year the measurements were 495 taken, changes to the La Bedoya spring channel for water distribution, and possible differences in flow-measurement methodology.

Contribution of groundwater to river flow
While springs showed very little isotopic variability, river isotope data was more variable (Figure 4). This can be expected for surface runoff since streams and rivers integrate many different flowpaths and show an immediate response to precipitation 500 events during the wet season causing large variations in surface water isotopic values depending on precipitation isotope values. In comparison, the response of springs to precipitation events is slower since groundwater response times are controlled by aquifer diffusivity and are therefore lagged relative to surface-water responses. The upstream reach of the Río Andamayo (ATA) in Chiguata showed a depleted isotopic composition during the wet season (March 2019 and February 2020), which likely indicates the direct runoff input of high-elevation rain. The Río Socabaya (SOC) shows a more depleted isotopic value 505 during February 2020 as the Río Andamayo feeds into the Río Socabaya (Figure 4). The similarity in isotopic composition between rivers and nearby springs also suggests that the rivers are either being supported by discharge from springs or direct discharge from the same groundwater feeding the springs. This is especially true for the Río Characato (RCH), which shows very little change in its isotopic values (Figure 4) throughout our sampling period and is extremely similar to its nearest spring, Ojo de Characato (OJO, Table 2). 510

Insight into groundwater residence times
Two precipitation samples were collected and submitted for 3 H analyses during this study. The measured 3 H activity in modern rain from Arequipa (MID) was 1.4 TU and snow from the Pichu Pichu Volcano (PPI) was 2.2 TU. These values are comparable to other modern 3 H values found in this region of the Central Andes (Aravena et al., 1999;IAEA, 2012). For example, rainwater collected between 1984 and 1986 in northern Chile was reported to have 3 to 10 TU (Aravena et al., 1999), and precipitation 515 sampled between 2006 and 2012 in Lima, Peru had 3 H values that ranged between 2.5 and 5 TU (IAEA, 2012). The atmospheric breakthrough of 3 H associated with nuclear weapons testing in the 1950s and 1960s for South America peaked at approximately 60 TU in Cuiabá, Brazil in 1965 while equatorial monitoring stations typically had 3 H breakthrough activities less than 40 TU (Albero & Panarello, 1981). Although there are latitudinal dependencies in South America similar to those observed in North America, Cuiabá is located close to the same latitude as Arequipa making it ideal for comparison. In North America, the 520 atmospheric breakthrough of 3 H was much higher; the tritium breakthrough in Miami, FL, USA peaked at 384 TU in 1964 while the peak was over 3800 TU in Chicago, IL, USA. In principle, high-elevation, local-scale groundwater in the mountains surrounding Laguna Salinas should have a 3 H activity similar to that of high-elevation snow, 2.2 TU. For context, Moran et al. slow flowpaths in local high elevation recharge and groundwater mixing below the salar. The two lower elevation springs (OJO and BED) were also 3 H dead. Relatively old groundwaters are consistent with the nearly constant stable isotope values of the Chiguata and Characato district springs. While it is not possible to provide an accurate residence time based solely on 3 H data for these springs, we infer that the residence times of springs in the study area are likely greater than 60 years.
Ultimately, tritium-dead is ambiguous with respect to residence time; the water sample could be 100 years old or it could be 530 100 ka. We cannot confirm or dismiss the possibility of paleo-recharge from the Last Glacial Maximum with only tritium data.
Future age-dating work should consider using radiocarbon and/or chlorine-36 to provide better constraints on residence times.

Groundwater flowpaths
We propose that groundwater mixing within the fractured mountain block controls the Clvariability in this region. The observed patterns are not consistent with increasing mineral dissolution contributions along increasing flowpath length. Nor 535 are they invariant due to piston flow through the mountain block (Bresciani et al., 2018 provides a discussion on this topic).
Chiguata springs have higher Clconcentrations even though they emerge at a higher elevation than springs at Characato. Jenks & Goldich (1956) state Clrich groundwater in the region may be explained by weathering of halite crystals found in volcanic deposits, namely a salmon-colored sillar, one of several rhyolitic tuffs present in the Arequipa region. However, the salmoncolored sillar has not been mapped in the Chiguata District to our knowledge. In the absence of salt-bearing minerals, an 540 alternate explanation for this anomaly is that there is a stronger groundwater connection between the high-elevation salar (a source of Clenriched water) and Chiguata springs (Figure 9 and 10). Both the chemistry and isotopic composition of Chiguata springs point towards a mix of recharge from the mLaguna Salinas basin and MBR occurring on Pichu Pichu and potentially other surrounding peaks including Tacune through the salar basin.

545
We approximated the geochemistry of the groundwater that flows into the Laguna Salinas basin using the chemistry of the INK spring sampled at the salar during the dry season. The validity of using INK as an approximation for groundwater outflow from the Laguna Salinas basin is assessed here by critiquing the chemistry of INK against the geochemical processes responsible for the formation of the evaporite minerals in the salar. INK is much fresher (510 uScm) than surface salar wet season water (17900 uScm) and Tacune Spring waters average (4434 uScm). However freshwater springs (167-181 uScm) 550 from the north and eastern sides of the basin TSA and MNE (Pichu Pichu) could mix with either surface salar or Ubinas waters to create INK waters. INK has high levels (2.13 mg L -1 ) of boron (B) which can be explained by B-rich water that enters the salar and subsequent evapoconcentration within the salar during the dry season. Springs HUM and UBI discharging into the basin have high B (greater than 15 mg L -1 but outside of the analytical calibration used). In any case, the geochemical composition of the spring INK appears to be a mixture of saline waters in contact with evaporites and fresh waters whose 555 geochemical composition can be explained by rock-water interactions (i.e., groundwater flowing from the surrounding mountains and discharging into or around the salar). We observed a high chemical variability in springs surrounding Laguna Salinas that may be influenced by the mineralogy of the Tacune mountain block. Unfortunately, there is little-to-no information on the mineralogy of the rocks of Tacune. We conclude that INK serves as a reasonable approximation of the mixed salar basin groundwater exported via interbasin groundwater flow. 560 The presence of ulexite nodules in the salar sediments likely points to times of saline water downwelling and fresh water upwelling through the sediments. As stated in section 2.3, the type of evaporite deposits changes with depth in the salar. When the salar begins to evaporate in the dry season, gypsum (CaSO4*2H2O) and anhydrite (CaSO4) precipitate first, followed by halite (NaCl) and thenardite (Na2SO4) (following the sequence proposed by Garrett, 1998). This increases the concentration 565 of B in the remaining water, some of which likely infiltrates the lacustrine sediments. The occurrence of ulexite minerals at depths greater than 1.2 m (Garrett, 1998) below the lake surface suggests that the salar level has changed through time and consequently, the vertical movement of infiltrating water today slows once it reaches the black and green muddy clay layers at 1.2 m. Here, the B-rich water accumulates and ulexite begins to precipitate (Garrett, 1998;Muessig, 1958). Garrett (1998) states that the most plausible model for the formation of ulexite nodules as opposed to crystal formation requires the mixing 570 of upwelling cation-rich groundwater with downwelling (descending) B-rich water from the surface; the subsequent competition between cation-sorption and mineral precipitation in the clay layers favors nodule growth. Since INK discharges into the basin and is flooded during the wet season, this suggests that the salar serves as a local topographic low which would tend to enhance groundwater discharge or upwelling. Muessig (1958) inferred that the inyoite underlying the ulexite formed in place as a primary mineral from the influx of B-rich water from the nearby hot spring. This specific area of the Laguna and Munk et al. (2021). The evaporation rate during the dry season, 141.3 cm (ANA, 2013) is quite high; however, the influx of surface water to the salar during the wet season is temporarily larger than evaporation rates causing the salar water level to rise seasonally. Therefore, it is plausible that water can leak from the salar during the wet season.
In immature Andean salars, subsurface sediments are heterogenous creating non-isostatic conditions and barriers to flow 580 (McKnight et al., 2021). The heterogeneous nature of these salars facilitates the formation of freshwater lenses that are not dependent on up gradient flow but rather the result of density-driven flow between surface brines and freshwater recharged to the salar in the wet season (Munk et al., 2021). Large monsoonal rain events with high rainfall rates have resulted in infiltration of precipitation from the salar surface beneath the transition zone to the underlying halite aquifer in the Salar de Atacama (Boutt et al., 2016). Seepage waters from such events would appear as mixtures of fresh and brine water so-called transition 585 zone waters (TZW). We found that shallow inflow waters from Tacune (UBI) and TZWs (INK) were tritium dead suggesting long-flowpaths recharge and mixing occurs beneath the salar. Moran et al. (2019) similarly found that most inflow and TZWs in the Salar de Atacama are tritium dead suggesting that these rapid freshwater recharge events observed by Boutt et al. (2016) are a smaller fraction of the overall water budget. If salar seepage does occur during rapid rainfall events we do not have a representative sample from the local aquifer. Rather, INK is representative of tritium dead IBF out of the salar basin to 590 Characato and Chiguata springs.
We propose that groundwater recharged on the neighbouring peaks including Pichu Pichu, Tacune, and Pukasaya (the mountains to the north of Lagunas Salinas), and potentially (albeit unlikely) Ubinas flows toward the salar basin which is a local topographic low. Springs emerge around the basin on the Pichu Pichu, Tacune, and Pukasaya shores of the salar and the 595 springruns flow into the salar. Subsurface groundwater flowpaths also converge on the basin. The groundwater from subsurface flow and from springs mixes with Clrich water that is infiltrating beneath the salar during the wet season. The resulting Clrich groundwater mixture then flows out of the basin facilitated by extensive faulting in the headwater of the Río Andamayo (Thouret et al. 2001, Bernard et al., 2019Lebti et al., 2006). The groundwater discharges along a fault at the Chiguata springs.
The Río Andamayo is fault-bounded from Laguna Salinas to the city of Arequipa, providing the hydraulic connection between 600 Laguna Salinas and the Chiguata and NaCl Characato springs at lower elevations ( Figure 2).
In comparison, the groundwater which supports the Characato SO4 -2 springs is geochemically distinct from the Chiguata and Characto NaCl springs (Figures 5, 6, and 8). The chemical resemblance between Characato springs and high-elevation Pichu Pichu snow and springs (rock weathering dominance in Figure 6), as well as the isotopic similarities between Characato springs 605 and springs in the mid-elevation queñuales forest (Figure 3) indicate that the Characato springs are supported primarily by recharge occurring in the mid-to high-elevations of Pichu Pichu. The sample of Pichu Pichu snow had 14.2 mg L -1 of SO4 2-, which is higher than expected for typical snow, likely due to aeolian deposition of SO4 2from recent nearby volcanic eruptions like Ubinas. Studies in northern Chile have shown that volcanic eruptions can produce large amounts of air-fall tephra that is deposited in the surrounding mountains and endorheic basins (Warren, 2016). Such events have the potential to elevate sulfate concentrations of waters and snow. We infer that MBR occurring on Pichu Pichu and the queñuales forest zone supports groundwater flowpaths on the southwestern slopes of the mountain toward the city as well as flowpaths to the northeast into the Laguna Salinas basin. Groundwater flows through distinct sulfate-bearing volcanic deposits toward the Characato District.
The Characato springs emerge along several faults on the lower slopes of Pichu Pichu (Figure 2). It's unlikely that there is significant groundwater circulation on the southwestern slope of Pichu Pichu because this area has been mapped with a 615 landslide deposit overlying a pseudotachylite (Legros et al., 2000) that probably limits deep circulation.

Conceptual hydrologic models of high-elevation forest and salar connectivity to low-elevation springs
We identify two main recharge zones for the lower-elevation Characato and Chiguata springs of our study region based on isotopic and geochemical analyses: 1) MBR within and above queñuales forest at ~4000 m.a.s.l. and 2) recharge from the Laguna Salinas basin (Figure 9). We also identify two main groundwater flow pathways: 1) inter-basin groundwater flow 620 (IGF) from the Laguna Salinas basin that provides the characteristic higher Clconcentration to Chiguata and Characto springs along the Andamayo fault system (Figure 9), and 2) groundwater flowpaths from the Pichu Pichu Volcano to lower elevation springs in Characato and Chiguata (Figure 9).
Our results indicate substantial MBR within or above the queñuales forest, however, forest recharge zones are controversial. 625 Paired forest-logged catchments studies have often found reduced watershed discharge in forested catchments due to higher evapotranspiration rates (see review by Brown et al., 2005). Observations and ecohydrology modelling of the relationship between canopy cover and MBR indicate that snowpack shielding and decreased sublimation may increase recharge in mountain forests (Magruder et al., 2009;Biederman et al., 2015). In general, the relationship between vegetation, water yield and MBR remains uncertain (Markovich et al., 2019), even as differences in tree types in a single study region have been 630 shown to change water yield (LaMalfa and Ryle, 2008). Therefore, future studies should investigate the ecohydrology of the queñuales forests and their role in MBR.
There have been several proposed hydrological conceptual models for other similar high-elevation closed-basin salars and their influence on lower elevation springs in northern Chile. Some prior studies suggest that there is some degree of 635 hydrogeologic connectivity between high elevation salars and lower elevation groundwater (Magaritz et al., 1990;Risacher et al., 2003;Herrera et al., 2016;Jayne et al., 2016); however, other studies reject this conceptual model (Uribe et al. 2015, Scheiling et al, 2017). Our conceptual model conforms with the former, for example, the Herrera et al. (2016) model in the Laguna Tuyajto of northern Chile, suggesting that closed-basin salars are not simple evaporation pans but instead leakage recharges groundwater flowpaths that support lower elevation springs. Our conceptual model is in partial agreement with the 640 findings from local research that identified the zone of groundwater recharge at the Pichu Pichu Volcano (Peña, 2018).
However, our chemical and isotopic data, as well as inference from fault connectivity, identifies the high-elevation Lagunas Salinas closed-basin salar as an additional contributor to groundwater recharge for lower elevations springs and suggests that inter-basin groundwater flow is an important hydrogeological process and an influence on the yearlong flow and chemistry of these springs. 645 isotopic signal of high-elevation recharge. It seems plausible that the Laguna Salinas basin recharge is a mixture of groundwater flowpaths that originate in the surrounding mountains, converge beneath the salar (local topographic low), and mix with wetseason recharge in the salar (leakage from the lake). Ultimately, the isotopic variability of precipitation and mineralogy of Tacune and the surrounding mountains located north of the salar are poorly quantified. Future studies should: 1) investigate 660 the vertical hydraulic conductivity of these lacustrine sediments and quantify their spatial variability in Laguna Salinas, 2) quantify the spatial variability and elevation-dependency of precipitation and the stable isotopic composition of precipitation in the mountains surrounding Laguna Salinas, 3) quantify the lithology and mineralogy of the surrounding mountains, and 4) install equipment to close a water balance on the closed basin.
Our study shows that the Lagunas Salinas basin is not a a hydrologic dead-end. Instead, it exports a mixture of groundwater from the surrounding mountains and saline water from the salar via interbasin groundwater flow. The salar basin receives groundwater year-round from two primary sources: subsurface flowpaths from the surrounding mountains and springs that emerge around the perimeter of the salar and whose springruns convey water to the salar. However, the salar basin only receives surface runoff during the wet season causing the water level in the salar to increase. Our conceptual model states that some 670 portion of saline surface water from the Laguna Salinas salar infiltrates the lacustrine sediments during the wet season, mixes with groundwater from the surrounding mountains, and is incorporated into the deeper groundwater flow system. This mixture of water then flows out of the basin by extensive faulting along the Rio Andamayo and is brought to the surface in the Chiguata District by faults which crosscut Rio Andamayo where it supports several spring systems. This finding indicates that highelevation salars may be important sources of recharge supporting low-elevation springs. Recharge area protection is 675 increasingly critical to the sustainability of mountain springs and streams and their associated ecosystems and our data calls attention to careful consideration of connectivity between other high-elevation salars and low-elevation springs in future hydrogeologic studies Future work should 1) investigate the proposed hydrogeological connection between the salar basin and the Chiguata springs, 2) install wells and instrument the salar basin to better quantify groundwater flow into and out of the salar, and 3) improve the mineral database of and expand geologic mapping of the Tacune and Pukasaya mountain blocks. The 680 data presented here provides a framework for protecting the recharge zones surrounding Chiguata and Characato and the suggested future work would strengthen or refine that framework.
The importance of the queñuales forest, adjacent to Pichu Pichu Volcano, for groundwater recharge of low-elevation springs also highlights the need to consider careful management of this natural ecosystem. Water resource planning including that of 685 Chiguata springs, one of which is a main drinking water source to the city of Arequipa (La Bedoya spring), must consider the influence of changes in land use not only at Laguna Salinas where mineral extraction companies currently operate, but also in the mountain block, in and above the queñuales forest.. Potential changes in precipitation patterns at the high-elevation closedbasin Laguna Salinas and Pichu Pichu Volcano could have impacts on groundwater recharge and long-term maintenance of these lower elevation springs. This study also revealed that there is long-term stability of groundwater in this arid region. 690 Stable isotope measurements of springs and rivers, river discharge, and tritium data support the existence of long-flow paths with water residence times of a few decades old or longer. Thus, these data suggest that regional groundwater may provide a stable water resource over the next few decades. While our findings are specific for this region in southern Peru, the implications of climate change, high elevation forest ecosystem degradation, and influence of the relatively unexplored factor of IGF to low elevation springs in the Central Andes may translate to other regions of the Andean plateau and Western 695 Cordillera.
Our research informs the origin and flowpaths of groundwater resources in this region; however, several questions remain. For instance, what is the percent contribution of each identified recharge zone to spring maintenance and what is the contribution of rain versus springs to river flow? Water managers would greatly benefit from learning the answer to these questions to focus 700 their management and conservation efforts of both spring and river waters that are of high importance to socio-economic activities of the region. The combination of isotopic and chemical-based tracers with traditional discharge monitoring, subsurface hydrogeologic mapping, and monitoring of hydraulic head data may be useful techniques to address these questions.
However, the use of the latter becomes difficult in remote, poorly accessible areas such as those found in many areas of our study. Finally, another question that remains is the presence and extent of pre-modern groundwater recharge in this previously 705 glaciated region and the potential influence of paleorecharge to low elevation spring maintenance, which would have significant implications for sustainable water management in this region. In this arid region of southern Peru, water resources research should continue to investigate the processes that control groundwater and surface water sources, and how to best protect and manage them for future use.

Acknowledgments 710
This work was funded by the Universidad Nacional de San Agustin (UNSA), Peru through the Arequipa Nexus Institute for Food, Energy, Water, and the Environment. The Nexus project director Dr. Victor Maqque was instrumental in nurturing this international collaboration. We thank Alexandra L. Meyer and Janine M. Sparks for their assistance in the stable isotope laboratory.

Author contribution 715
OAC: Data collection, laboratory analysis, data analysis and interpretation, and drafting manuscript. EJO: Data collection, laboratory analysis, experiment design, data interpretation, and manuscript revision. MDF and LRW: Experiment design, data interpretation, manuscript revision, and secured funding for the project. SAZ: Regional geologic knowledge, data collection, manuscript revision. JDR: Regional geologic knowledge, manuscript revision. WRQ, CSM, and MAC: Data collection, data reporting, and manuscript revision. Final version of the manuscript was approved by all authors.