Origin and hydrochemical characteristics of groundwater in the Northeastern Patagonia, Argentina: the relationship with geomorphology and soils

Abstract

In arid zones, geomorphology and soils play a fundamental role in groundwater surveys as they condition the recharge phenomenon and some processes that modify water chemistry. The objective of this work was to identify the groundwater provenance and the relationship between its chemistry and isotope contents with the geomorphology and soil in the northeastern Patagonia, Argentina. Over an area of 10,600 km2, groundwater levels and major ionic and stable isotopic contents were measured. The main geomorphological units were mapped using satellite images and digital elevation models. In soils, pedogenetic carbonate contents (PC) and clay accumulation index (CAI) were measured. Different hydrochemical facies were identified in relation to geomorphological units, being the Cl–SO4–Na and Cl–Na ionic types dominant in fluvial terrace plains (terrace associations, TAs). The Cl–SO4–Na types are the most saline groundwaters and are coincident with the TA where Petrocalcids are the dominant soils. With less salinity contents, Cl–SO4–Na and Cl–Na types are the groundwaters associated with TA where the dominant soils are Natrargids and Haplocalcids. The only sector with Cl–HCO3–Na is those with fresh water coincident with the Aeolian field unit, where Psamments soils develop. Likewise, groundwater is isotopically differentiated in response to the origin being mostly allocthonus in the fluvial terrace plains and from local recharge in the Aeolian fields. The fluvial terraces are gravel deposits that would favor a local recharge, but this is prevented both by pedogenic carbonate and clay contents which developed in the upper part of the deposit. In this way, the measurement of pedogenetic carbonates and clays becomes soil properties of utmost importance to be considered in groundwater prospecting in arid regions worldwide.