Evidence for high-elevation salar recharge and interbasin groundwater flow in the Western Cordillera of the Peruvian Andes
Authors: Alvarez-Campos Odiney , Olson Elizabeth J. , Welp Lisa R. , Frisbee Marty D. , Zuñiga Medina Sebastián A. , Díaz Rodríguez José , Roque Quispe Wendy R. , Salazar Mamani Carol I. , Arenas Carrión Midhuar R. , Jara Juan Manuel , Ccanccapa-Cartagena Alexander , Jafvert Chad T. 
Published: January 2022

Abstract. 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 flow paths that convey groundwater to
lower elevations where the springs emerge remain poorly quantified in the
volcanic mountain terrain of southern Peru. In this study, we identified
recharge zones and groundwater flow paths 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 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 flow paths that
support spring flow is relatively stable with time. The chemistry of springs
in the low-elevations and mid-elevations (2500 to 2900 m a.s.l.) point towards a mix of
recharge from the salar basin (4300 m a.s.l.) and mountain-block recharge (MBR)
in or above a queñuales forest ecosystem at ∼4000 m a.s.l. on
the adjacent Pichu Pichu volcano. Springs that clustered along the Río
Andamayo, including those at 2900 m a.s.l., 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-/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 groundwater flow paths 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 on the
down-valley water quality and quantity.