Groundwater chemistry within Arequipa, Peru in the Characato, Chiguata, and Lagunas Salinas study areas

<p>Data supplement for "<strong>Evidence for high-elevation salar recharge and interbasin groundwater flow in the Western Cordillera of the Peruvian Andes"</strong> accepted to Hydrology and Earth System Sciences. This project contains groundwater chemistry and field observations analyzed in the manuscript. </p>

<p>Complete list of publication authors supported by the Arequipa Nexus Institute, a collaboration between Purdue University and Universidad Nacional de San Augstín de Arequipa: Odiney Alvarez-Campos, Elizabeth J. Olson, Lisa R. Welp, Marty D. Frisbee, Sebastián A. Zuñiga Medina, José Díaz Rodríguez, Wendy R. Roque Quispe, Carol I. Salazar Mamani, Midhuar R. Arenas Carrión, Juan Manuel Jara, Alexander Ccanccapa-Cartagena, and Chad T. Jafvert</p>

<p>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 (δ<sup>18</sup>O, δ<sup>2</sup>H, and <sup>3</sup>H) 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 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 low- and 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 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<sup>-</sup>/SO<sub>4</sub><sup>-2</sup> 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 groundwater flowpaths from the surrounding mountains converge in the basin and some mixture of this water supports groundwater flow out of the salar basin via interbasin groundwater flow. In this arid location, high-elevation forests and the closed-basin salar are important sources of recharge supporting low-elevation springs. These features should be carefully managed to prevent impacts to the down-valley water quality and quantity.</p>