CONICET | Buscador de Institutos y Recursos Humanos

The estimation of lake hydrological characteristics such as evaporation/in fl ow ratios and water residence time becomes necessary for understanding cycling and potential retention of natural and anthropogenic substances into the lake. The aim of this work was to estimate the evaporation loss and the water residence time of a temperate shallow lake based on the water isotope mass balance approach. One representative freshwater temperate shallow lake from the Argentinian Pampa Plain was selected. Groundwater, lake and stream samples (N = 56) were collected for δ2 H-H 2 O and δ18 O-H2O determinations. Moreover, water level fluctuations of the lake and its in flow stream were recorded with data loggers. Both the δ2 H and δ18 O relationship and d-excess of lake water indicated evaporation. Water isotopes and daily stream fl ow data recorded in the in fl ow stream evidenced groundwater contribution to Los Padres Stream. Monthly evaporation as a fraction of in fl ow estimations of the lake water indicated that about20?25 ± 12% lake water was lost through lake surface evaporation and revealed that hydrologic balances were regulated mainly by changes in water in fl ow rather than evaporation. A mean residence time of 1.11 ± 0.65 year was also calculated. This lake hydrological information is relevant for the region and crucial to improve water management plans.