GEOCHEMICAL STUDY OF A CRATER LAKE (PAVIN LAKE, FRANCE) - TRACE-ELEMENT BEHAVIOR IN THE MONIMOLIMNION

Meromicticity of Pavin Lake leads to a consequential dissolved major-a nd trace-element enrichment of the lower layer (monimolimnion) of the lake. In a previous work, we showed that steady state is established w ithin this permanently anoxic bottom layer and profiles for major spec ies could be represented by an advection-diffusion model. In this pape r, results concerning the contents of 16 trace elements determined by ICP-MS are discussed in terms of variations through the redox interfac e and above the sediment-water interface. Trace alkalis and boron as e xpected are conservative. Arsenic, nickel and cobalt are dissolved bel ow the redox interface from Mn-and/or Fe-oxyhydroxide precipitated in the mixolimnion. Results also show clearly that barium, aluminium, cer ium, lead, uranium, lanthanum, vanadium, copper and molybdenum are fir st released into the solution from the sediment before being scavenged in the bottom water. Furthermore, common behaviour between trace meta ls and dissolved organic carbon may introduce to a better understandin g of transfer mechanisms. Finally, dissolved element fluxes rising up in the monimolimnion are calculated.