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Climatic and anthropogenic effects on the sedimentation and geochemistry of Lakes Bourget, Annecy and L�man

1982; Springer Science+Business Media; Volume: 91-92; Linguagem: Inglês

10.1007/bf00000063

1573-5117

Jean-Pierre Vernet, P.‐Y. Favarger,

Heavy metals in environment

During the last glaciation, the Rhone glacier extended as far as the region of Lyon and covered Lakes Bourget, Annecy and Léman. Glacial retreat successively freed Lakes Bourget and Annecy, it reached Geneva around 14 000 B.P. and the head of Lake Léman at about 12 000 B.P. Deposits situated between Nyon and the foot of the Jura provide a complete palynological zonation and serve as a type section for the lake core studies. A palynological horizon (about 1 800 A.D.) has been found in Lake Bourget and wood has been dated at 3 230 ± 65 B.P. (14C) in a core from Lake Léman. Three 6 m cores from each lake were sampled together with many 0.5 m cores from Léman. The short Lake Léman cores have been dated by 137Cs and provide a precise indication of changes in the basin during recent decades. Holocene climatic variations are evident in the Léman cores and are reflected by concentrations of carbonate and organic carbon which increase at the end of the Alleröd and reach a maximum in the Atlantic Period (climatic optimum). Human settlement on the shores of Lake Annecy is shown by increases in heavy metals; increased sedimentation rates suggest settlement at the beginning of the Christian era. All the cores show increases in the organic matter and nutrients; from the turn of the century in the Léman, and later for the other lakes where eutrophication started only a few decades ago. NAI-P shows a very recent increase, around 1965 in the Leman. Heavy metals (Hg, Cd and Pb) show increases at about 30 years ago in Annecy, at about the turn of the century in Lake Léman and in the mid-19th century in Lake Bourget.