Factors and processes controlling hydrochemistry and evaporitic deposits in hypersaline wetland-shallow lake systems

ACOSTA, ROSARIO; CAROL, ELEONORA; BORZI, GUIDO; CELLONE, FRANCISCO; ÁLVAREZ, MARÍA DEL PILAR

HYDROLOGICAL PROCESSES

JOHN WILEY & SONS LTD

Lugar: LOndres; Año: 2023 vol. 37

0885-6087

Three wetland-shallow lakes were studied with the aim of analysing the processesand factors that control hydrochemistry and evaporite deposits in them in basins ofthe Pampean Plain, Argentina. In this sense, water balances and analysis of the watercontent of the lakes with normalized water difference index were made, andgeologic-geomorphological characteristics and groundwater flows were defined.Groundwater, surface water and evaporite samples were taken, along with sedimentsamples from wetland-shallow lakes and surroundings. In situ pH, electrical conductivityand temperature, and laboratory chemical determinations of major ions of thewater were measured. x-ray diffraction (XRD) and scanning electron microscope(SEM)-energy dispersive spectroscopy (EDS) analyses of evaporite and sediment sampleswere carried out. The results obtained allow the identification of two differentsystems. One of them is represented by Leubuco wetland-lake basin, which is topographicallyhigher and smaller than the other system, with Na-HCO3 and Na-Cl/SO4groundwater inflows, with high concentrations of Ca2+ and Mg2+. In periods of highevaporation, the regional water table drops, and due to its topographic position, thelake dries. These determine the formation of thick layers of halite associated withmagnesium salts on surface, and gypsum layers interbedded with clastic sediments.The other system involves de la Sal and Chasilauquen wetland-lake basins, whichhave larger extensions. They receive Na-HCO3 and Na-Cl/SO4 groundwater inflow,but with low Mg2+ and Ca2+. Their lower topographic position determines that evenduring deficit periods, the water table intercepts the lakes surface and therefore,lakes have a shallow surface water level almost all the year, which is hypersaline, Na-Cl type. These systems only have thin evaporite crusts, composed of halite and thenarditeat the edges of the lakes, and the formation of Ca-Mg sulfates is notobserved. It is concluded that topographic position, basins size, geology, groundwaterinflow and evaporation are the main processes and factors controlling hydrochemistryand evaporitic deposits.