HISTORICAL VARIATIONS IN LEAD FLUXES IN THE PYRENEES (NORTHEAST SPAIN) FROM A DATED LAKE SEDIMENT CORE

Variations in Pb concentration in lake sediments reflect changes in th e fluxes of this element in the past. A sediment core from a lake in t he Pyrenees (Lake Redo at 2,240 m a.s.l., NE Spain) was studied, with the aim of reconstructing past environmental and climatic conditions i n the lake and its catchment area. The core was dated using both Pb-21 0 and C-14. A surface peak of Pb concentration, which was about 10 tim es higher than the background level, was found. This peak is attribute d to mining activities since the beginning of this century. Although P b pollution due to the combustion of gasoline is expected to be presen t, no evidence can be deduced from Pb isotope ratios of sediment due t o the masking effect of Pb from mines. A second peak appeared in a dee per layer, with a maximum Pb concentration of about 17 times higher th an the background level. The origin of this peak is unclear. All evide nce suggests that the ancient peak is due to mining operations in the central Pyrenees area, which were not documented historically.