The interplay between total mercury, methylmercury and dissolved organic matter in fluvial systems: A latitudinal study across Europe

International audience ; Large-scale studies are needed to identify the drivers of total mercury (THg) and monomethyl-mercury (MeHg) concns. in aquatic ecosystems. Studies attempting to link dissolved org. matter (DOM) to levels of THg or MeHg are few and geog. constrained. Addnl., stream and river systems have been understudied as compared to lakes. Hence, the aim of this study was to examine the influence of DOM concn. and compn., morphol. descriptors, land uses and water chem. on THg and MeHg concns. and the percentage of THg as MeHg (%MeHg) in 29 streams across Europe spanning from 41°N to 64 °N. THg concns. (0.06-2.78 ng L-1) were highest in streams characterized by DOM with a high terrestrial soil signature and low nutrient content. MeHg concns. (7.8-159 pg L-1) varied non-systematically across systems. Relationships between DOM bulk characteristics and THg and MeHg suggest that while soil derived DOM inputs control THg concns., autochthonous DOM (aquatically produced) and the availability of electron acceptors for Hg methylating microorganisms (e.g. sulfate) drive %MeHg and potentially MeHg concn. Overall, these results highlight the large spatial variability in THg and MeHg concns. at the European scale, and underscore the importance of DOM compn. on mercury cycling in fluvial systems.