IDENTIFYING GROUNDWATER RECHARGE ZONES IN WESTERN CORDILLERA OF THE CENTRAL ANDES OF SOUTHERN PERU

Groundwater plays a vital role in sustaining socio-economic activities (e.g. drinking water, agriculture, mining, etc.) in the arid region of Arequipa, Peru. However, the sources of groundwater recharge that support spring discharge in this region remain uncertain. The objectives of this study are to identify sources of recharge (snow vs rain vs glacial melt/paleorecharge), recharge zones, and groundwater flowpaths east of the city of Arequipa in the Central Andes of southern Peru by using natural geochemical and isotopic tracers in springs, surface waters (rivers/lakes), and precipitation (rain/snow). Water samples were collected from March 2019 through February 2020. We obtained monthly samples from six springs, bimonthly samples from four rivers, and various samples from high-elevation springs during the dry season (October 2019). We analyzed stable water isotopes (δ¹⁸O and δ²H) and general chemistry of springs, rivers, local rainfall, and snow from Pichu Pichu volcano. The monthly isotopic composition of spring water was invariable over time, suggesting that the springs receive a stable source of groundwater recharge. Isotopic composition of springs in the district of Chiguata (~2900 masl) point towards a mix between recharge from a high-elevation, closed-basin lake (~4300 masl) and mountain-block recharge in/above the queñuales forest (~4000 masl) on the Pichu Pichu volcano. Chiguata springs also have higher chloride concentrations, even though they are at a higher elevation than springs at Characato which emerge at a lower elevation (~2500 masl), highlighting their greater connection to the brine lake. Similarities in isotopic composition between the weighted average of rain (δ¹⁸O = -9.5‰, δ²H = -65.7‰) and springs at a high-elevation forest as well as springs in the district of Characato indicate that these springs are supported primarily by mountain- block recharge from snow and rain. Higher sulfate concentrations of Characato springs suggest that groundwater is flowing through a different set of flowpaths that is likely influenced by the presence of volcanic deposits. Our findings provide valuable information on the flowpaths and sources of recharge that support springs and how these may be impacted by climate change. Our data suggest that high-elevation forests may be important for groundwater recharge, thus these recharge zones should be protected to prevent impacts to the down-valley springs.