CONICET | Buscador de Institutos y Recursos Humanos

ABSTRACT  The Sistema de las Encadenadas de Chascomús, Salado River drainage basin lies in the geomorphologic unit called Pampa Deprimida in the Buenos Aires province, Argentina. The Pampeano Plio-Pleistocene sediments contain the aquifer unit. This system, dynamic and tied to climate conditions is formed by interconnected shallow lakes connected with the Salado River. The water level of the lakes depends on the hydrological cycle, being the inputs: precipitation, streams, groundwater inflow and surface runoff and the outputs: evaporation and stream outflow. During flood periods precipitation is stored in depressions forming shallow lakes and marshes. Infiltration is high due to regional lack of slope and soil characteristics, and the phreatic is near surface. Groundwater and surficial water are strongly interrelated. This paper studies the relation between them by environmental stable isotopes (2H, 18O). The local meteoric water line (LMWL) is δ2H=8 δ18O+14 obtained from Ciudad Universitaria station, Buenos Aires city. This LMWL was established from a long record of National Network Collector for Isotopes in Precipitation belonging to the GNIP. The groundwater isotopic composition for all samples is relatively constant : -5.0 and 30 for δ18O and δ2H, respectively, indicating their meteoric origin. Nevertheless, small fluctuations in the obtained values are probably due to evaporation of local precipitation prior to infiltration. Recharge waters reflect the mean precipitation with reasonable fidelity. The stream and lake waters fit on an evaporation line (δ2H =5.9 δ18O -1.2), indicating the groundwater contribution. The isotopic results suggest that during summer, when the precipitation-evaporation balance is negative, the surface water hydrochemistry is governed by the evaporation process. These results are in agreement with those presented in a recent work. The origin of groundwater is meteoric and the shallow groundwater constitutes the base flow of surficial water, fact that had been previously assumed by other authors.

enviar mensaje