Variaciones estacionales de la salinidad del agua subterránea en las márgenes de la Salina Grande de Villafáfila (Zamora)

Abstract

Villafáfila lakes have been traditionally used for salt extraction by concentration of their brackish waters. Nowadays the lakes are nourished by rain water, by brackish waters from springs related to regional groundwater flows, and by the dis- charge of fresh groundwaters coming from the hills surrounding the lakes. In this work are shown the results of two geophy- sical campaigns of time-domain electromagnetic method, carried out during summer, when lakes dry out and during winter when lakes contain water. These results are accompanied by direct measurements of the groundwater electric conductivity. During winter, the freshwater (recharged on the hills) -brackish water (regional groundwaters) interface slope is more gentle than during the summer when it is more steep. Groundwaters in the lake margins are recharged by rain during winter and contain fresh waters close to the ground surface. In contrast during summer, evaporation produces salt concentration in the capillary zone. Besides, a 300 m retreat of the fresh groundwaters towards the hills. It is interpreted that high evaporation during summer produces groundwater pumping through capillarity in the lowlands surrounding the lakes. This provokes about 20 m uplift of the freshwater-brackish water interface.