CONICET | Buscador de Institutos y Recursos Humanos

Pampean streams in the humid region are the discharge point of groundwater flow systems, which is known from piezometric studies and the application of chemical and isotopic tracers.An approximation can be obtained from water dating, considering that groundwater is "oldwater", and the determination of the 222Rn, which due to its short half-life (3.8 days) is indicative of recent discharge. The Vivoratá and La Ballenera creeks were selected for this study, both having their sources on the slopes of Tandilia and traveling a few dozen of km until they reach the sea, without receiving any tributary. Samplings were done in August 2017, after several days without precipitation, and at various points in each stream. Flow rates and physicochemical parameters were measured, and samples were taken. Major ions were determined by standard methods, stable isotopes by laser spectroscopy, and 222Rn with a RAD7 radon detector, in the laboratory of the Hydrogeology Group. The CFCs were analyzed by GC-ECD at the University of Utah. The results show the contribution of groundwater: increase of discharge and electrical conductivity downstream, water dated withCFCs in about 30 years, and concentrations of 222Rn between 1 and 3 Bq.L-1, increasing downstream corresponding with higher concentrations of 222Rn. In the La Ballenera stream, the existence of a lake that retains the flow, determines low 222Rn concentrations by radioactive decay.