SS3.17 Global Mercury Cycling: From Natural to Anthropogenic Sources
Date: Tuesday, June 11, 2002
Location: Poster Session - VCC
Begin Maxime, , , Universite du Quebec a Montreal, Montreal, Canada, 
Lucotte, M, , COMERN, Institut des Sciences de l'Environnement, Universite du Quebec a Montreal, Montreal, Canada,
CanuelR, COMERN, Institut des Sciences de l'Environnement, Universite du Quebec a Montreal, Montreal, USA,
Methylation of mercury in flooded soil of hydroelectric reservoirs in James Bay (Québec) - Canada
We observed the evolution of MeHg concentrations in flooded soil as a function of flooding time, depth and temperature. Flooded podzols and peatlands have been sampled at the bottom of reservoirs of northern Québec. The study has revealed a net Hg methylation during the first years of flooding. The percentage of methylated Hg in podzols rises fom 10-15 times after 4 years of flooding, and up to 30 times after 13 years. The long term net Hg methylation is weaker in peatlands (increase of 15 times). These observations show that flooding causes the methylation of a fraction of the inorganic Hg present in the soil before flooding. The progressive accumulation of MeHg in upper soils during the first years of flooding suggests that the methylation processes are faster than those of demethylation. MeHg remains stable in its new environment and only represents a source of contamination for the reservoir food chain if it is made bioavailable either after suspension of the organic horizons of soil or along with the outgoing of benthic organisms from the upper layers of flooded soil.