Multi-isotope (δ~2H, δ~(18)O,δ~(13)C-TDIC, δ~(18)O-TDIC, ~(87)Sr/~(86)Sr) and hydrochemical study on fractured-karstic and detritic shallow aquifers in the Pampean region, Argentina

摘要

Fluxes between fractured-karstified and detritic aquifers are commonly poorly understood in many environments. These two types of aquifers are in contact in the southeastern Pampean region in the Argentine Buenos Aires province, and the aim of this work is to analyze their relationship contributing to improve the hydrological model. A joint application of hydrochemical and multi-isotope (delta H-2,delta O-18,delta C-13-TDIC,delta O-18-TDIC,Sr-87/Sr-86) tools was used. TDIC,delta H-2,delta O-18 and delta C-13-TDIC allowed differentiating two main end members. Water in the Pampeano aquifer (PA) which is transferred from the fractured-karstic aquifer (F-KA) is characterised by high TDIC around 500-700 mg/L, isotopically depleted in(18)O (about -5.5 parts per thousand) and high delta C-13-TDIC (around -10.0 parts per thousand). The other end member is direct recharge water infiltrated into the PA with TDIC ranging from 400 to 500 mg/L, slightly enriched in(18)O (delta O-18 = -4.8 parts per thousand), and delta C-13-TDIC in the range of soil CO(2)as a result of reactions with calcrete concretions (from -20.0 to -9.0 parts per thousand). Dolomite dissolution is the main process controlling the chemistry of the low-mineralized (Mg-Ca-HCO3) waters, whereas high-mineralized (Na-HCO3) waters are strongly influenced by ion-exchange reactions with adsorbed Ca(2+)and Mg(2+)and by evaporation.