GEOCHEMICAL STUDY OF A CRATER LAKE - PAVIN LAKE, FRANCE - IDENTIFICATION, LOCATION AND QUANTIFICATION OF THE CHEMICAL-REACTIONS IN THE LAKE

A study of the main geochemical characteristics of the Pavin crater la ke was performed in September 1992. Associated with previous results o n the hydrochemical budget of the lake, the present study points out t hat: (1) in the mixolimnion, the major reactions are photosynthesis, r emoval of silica by diatoms, iron oxidation and alkali and alkaline-ea rth incorporation in a solid phase; (2) the major reduction reactions occur within the sediment and the products of the reaction are brought to the lake by diffusion; (3) some reactions: silica dissolution, man ganese oxide reduction, sulfate-sulfide transformations, iron and phos phate precipitation occur within the monimolimnion. A complete budget of transfers and chemical reactions is presented for some components s uch as silica.