Session Title :

Why do ecosystems retain mercury? The role of redox transformations in controlling mercury mobility in terrestrial and aquatic environments

Synopsis:

This session will focus on recent advances in abiotic and biotic redox transformations of mercury. We are inviting contributions dealing with the mechanistic determinants of redox reactions and the resulting effects on Hg mobility.

Description :

The balance of Hg oxidation and reduction largely determines its accumulation in ecosystems. Hg redox reactions control the abundance of elemental Hg that is one of the most volatile Hg species. As such, the relative importance of reduction and oxidation reactions has the potential to also control the residence time of mercury in a given environment. However, major gaps of knowledge still remain before we can properly model and predict the contribution of redox reactions to Hg cycling. While photochemical reactions are important in driving Hg redox cycling at interfaces with the atmosphere, our current knowledge mostly resides in processes controlling Hg0 production. We know very little of the fate of the newly produced Hg0 in natural waters, namely what are the chemical and microbial controls of Hg0 oxidation. Moreover, and while some important contributions were made in the last few years, we still have a poor understanding of the processes that can control Hg redox transformations deeper in the water column of water bodies or within sediments, where photochemical processes are unlikely. The relevance of these processes is often overlooked. However, they are of paramount importance as they change Hg speciation within compartments known to be conducive to Hg methylation. As such, they also indirectly control Hg retention in ecosystems by influencing the pool of Hg likely available to methylation.