Geochernical study of a crater lake (Pavin Lake, France): Trace-element behaviour in the monimolimnion

Meromicticity of Pavin Lake leads to a consequential dissolved major-and trace-element enrichment of the lower layer (monimolimnion) of the lake. In a previous work, we showed that steady state is established within this permanently anoxic bottom layer and profiles for major species could be represented by an advection-diffusion model. In this paper, results concerning the contents of 16 trace; elements determined by ICP-MS are discussed in terms of variations through the redox interface and above the sediment-water interface. Trace alkalis and boron as expected are conservative. Arsenic, nickel and cobalt are dissolved below the redox interface from Mn-and/or Fe-oxyhydroxide precipitated in the mixolimnion. Results also show clearly that barium, aluminium, cerium, lead, uranium, lanthanum, vanadium, copper and molybdenum are first released into the solution from the sediment before being scavenged in the bottom water. Furthermore, common behaviour between trace metals and dissolved organic carbon may introduce to a better understanding of transfer mechanisms. Finally, dissolved element fluxes rising up in the monimolimnion are calculated.