Hydrochemistry of Pampean lakes

PASQUINI, A.I.; CAMPODONICO, V.A.; MARTIN ME; LECOMTE KL; ALVAREZ, BRENDA Y.; DAPEÑA, C.; CAROL E

Pampean lakes

Springer

Año: 2025; p. 303 - 337

Numerous shallow lakes are present in the Argentine Pampa plain. In the Southern Pampa plain most are freshwater or subsaline lakes, whereas in the Northern and Western Pampa plain lakes range from subsalines to hypersalines, with higher TDS concentration during the wet season, when water balance is usually negative, than in the dry season. Pampean lakes are mostly alkaline, without significant regional or seasonal pH variations. The waters of most Southern Pampean lakes are bicarbonate-sodium-type, whereas Northern Pampean lakes range from bicarbonate-sodium-type to chloride-sodium-type. Western Pampean lakes exhibit the widest compositional range. Weathering and evaporation-precipitation processes mainly control the water chemistry. Most of them are oversaturated in Ca and Mg-carbonates, theoretically evolving from calcite composition towards the precipitation of Na-carbonates, with halite as the final precipitate. Monovalent ions (Cl-, K+, and Na+) are mainly present as free aqueous ions, whereas HCO3- is the most abundant carbon species. Other elements (S, Ca, and Mg) tend to form complexes. The stable isotopic compositions also evidence evaporation processes, more intense during the wet season (austral summer). Groundwater-surface water interactions in several Northern and Western Pampean lakes, modelled using environmental tracers (i.e., δ18O and 222Rn), indicate groundwater discharge occurring at different scales.