Surface-groundwater exchange in a sand dune lake in the Dry Pampean Plain, Argentina: Stable isotopic evidence.

ECHEGOYEN CV; CAMPODONICO, V.A.; LECOMTE KL; JOBÁGGY EG; YACIUK P; SEPÚLVEDA LD

HYDROGEOLOGY JOURNAL

SPRINGER

Lugar: Berlin; Año: 2022

1431-2174

Understanding the hydrological functioning of the scarce freshwater bodies of semiaridregions is crucial, especially in those areas affected by anthropic activities such as landuse changes. In the dry western edge of Argentina Pampean plains, a system of morethan one hundred shallow lakes of remarkable stability occurs. They exhibit low salinitycompared to those located in the more humid belt. It has constituted the main waterresource for humans from prehispanic times to the present. Stable isotopes were usedto establish the seasonal surface-groundwater interactions and the hydrologicalconditions in a lake of the Dry Pampean Plain (DPP), i.e., Lake Los Pocitos, tounderstand the mechanism that guarantees such resource. Results indicate thatevaporation mainly controls the isotopic composition of lake water, overwhelming theeffect of higher rainfall inputs during the wet (but also most evaporative) season. Theδ18O mass balance model indicates greater groundwater inflow to the lake during thedry season (~0.4 m month−1) compared to the wet season (~0.2 m month−1). Lakelevel decreased in the wet season due to the lowest groundwater inflow and thegreatest evaporation rate. Based on the proportion of water entering a lake that leavesthrough evaporation, Los Pocitos corresponds to a throughflow lake with a short waterresidence time (~0.47 years). These hydrologic conditions, along with freshwaterinputs from a dune located in the western margin of the lake, determine the existenceof this relatively stable and freshwater lake in the DPP where high evaporation ratesare registered.