Precipitation origin and evaporation of lakes in semi-arid Patagonia (Argentina) inferred from stable isotopes (δ18O, δ2H)

Stable isotope approaches are often used for estimating water balances of takes. Such studies require regional background information about hydrogen and oxygen isotope variability of takes and their potential inflows. Here, a stable isotope database (delta H-2 and delta O-18) is presented for estimating evaporation to inflow ratios (E/l) of takes in semi-arid southern Patagonia. Water samples of 23 takes and ponds located in the Patagonian steppe at about 52 degrees S were sampled during three subsequent austral summers. Two deep crater takes, Laguna Azut and Laguna Potrok Aike, were studied in more detail during a two-years monitoring. Furthermore, precipitation, groundwater and atmospheric water vapor were sampled for isotope analyses. Presented data imply that the isotopic composition of rainfall in southeastern Patagonia is predominantly determined by precipitation amount and moisture source area. For the investigated area, the first meteoric water and evaporation lines in delta H-2 vs. delta O-18 space are presented. The database was further used to estimate the water balances of the two crater takes, Laguna Azut and Laguna Potrok Aike, which are in the focus of recent pateoclimatic investigations. According to that approach about 50% and 60%, respectively, of the water entering Laguna Azut and Laguna Potrok Aike via surface and subsurface inflow evaporates. These results testify a considerable flow of take waters into the groundwater. (c) 2006 Elsevier B.V. All rights reserved.