Hidrogeoquímica e hidrología isotópica aplicada al estudio de la relación agua subterránea-agua supeficial en grandes cuencas: la cuenca del río Quequén Grande, Buenos Aires, Argentina

MARTÍNEZ, D. E.; DAPEÑA, C,; MASSONE, H,; PANARELLO, H.0.; LONDOÑO QUIROZ, O M,; FERRANTE, A.

Asunción, Paraguay

Congreso; VIII Congreso Latino Americano de Hidrologia Subterránea ALHSUD; 2006

ALHSUD

ABSTRACT The relationship between groundwater and surface water in widespreadcatchments is a factor of high importance in the evaluation and prevention ofhydrological phenomena affecting the sustainable economic development of theseareas. A better understanding of these catchments requires new contributions fromdifferent perspectives integrating information other than purely hydrologic, which arepoorly spatial distributed. This study seeks to characterize the groundwater-surface water relationship in the Quequén Grande river catchment, in the province of Buenos Aires, Argentina, applying hydrogeochemical and isotopic information. In order to achieve this, data corresponding to a hydrochemical sampling performed in 70 wells and 30 stream points during a flood period in summer 2002 were used. Since November 2004, a monitoring network was been installed, including four rainwater collectors (monthly samplings), five stream water sampling points (weakly sampling), and a variable number of monitoring wells. Major ions were analyzed and 2H, 18O y 3H isotopes measured in most of the samples. The resulting data were processed statistically and analyzed using conventional diagrams for hydrochemical and isotopic interpretation.The piezometric contours map for 2002 suggests a gaining behavior of the streams all over the catchment. Total dissolved solids show similar values for both groundwater and surface water indicating that most of the water flowing in water courses comes form discharge of groundwater caused more by rising piezometric levels than by concentrated rainfalls. Surface water samples taken in 2005 show a clear water type differentiation between the eastern and western sectors with bicarbonate water in the former and sulfate water in the later, due to dissolution of gypsum layers existing in the area. Groundwater shows a similar water type distribution confirming that the rivers are recharged by the aquifer. Phreatic levels in this period are about 2 m below the observed levels in 2002, then baseflow should be a lower proportion of total flow, which is in agreement with the measured total dissolved solids.  Isotopic composition of groundwater and surface water is in alignment with the global meteoric water line (GMWL). Groundwater shows a lower variability than surface water, probably due to the concentration of recharge in short periods. Applying this observation it is possible to calculate baseflow contribution using 18O as conservative tracer.