Determination of the "altitude effect" based on δ18-O and δ2-H as indicators of groundwater recharge, Cañete river basin

Abstract

Based on the results of stable isotope analysis δO-18 and δH-2 in water samples from springs, due to the similarity with the isotopic composition of the precipitation in height and according to the conservative character of the isotopes δO-18 and δH-2 and in reference to the altitude of the samples, it has obtained the isotopic values of the "altitude effect" and the identification of the recharge area for the sector under study. The samples have been collected in the upper part of the Cañete river basin (3490-4300 MASL), reaching an altitude difference between samples of 800 m. The isotopic values are affected by fractionation and systematic deviations (δ) with respect to the altitude as well as by the processes of evaporation and condensation prior to infiltration. For its interpretation, the isotopic analyzes have been performed by laser spectrometry in the IPEN laboratories and, have provided information on the height at which the recharge of the hydrosystem takes place. The "altitude effect" of the study sector is of the order of -0.45 o/oo for δO18 and -3.30 o/oo for δH2 per 100 m of altitude. Acco recharge zone has been obtained graphically based on diagrams and is located between 3600-4350 MASL area of the basin where the highest rainfall in liquid form occurs.