Mobilization and transformation of mercury across a dammed boreal river are linked to carbon processing and hydrology
Article [Version of Record]
Is part ofWater resources research ; vol. 56, no. 10.
Reservoirs are known to accelerate the mobilization and cycling of mercury and carbon as aresult of flooding of terrestrial organic matter, which can lead to environmental concerns at local andbroader spatial scales. We explored the covariation of mercury (Hg) and carbon (C) functional pools innatural and recently dammed portions of the aquatic network of the Romaine River watershed in NorthernQuebec, Canada, to understand how the fate of these elements varies across systems with contrastinghydrology and environmental conditions. We found that total Hg (THg) concentrations in surface waterswere relatively constant along the network, whereas both the concentrations and proportions of MeHgtended to increase in reservoirs compared to surrounding nonooded systems, and along the cascade ofreservoirs. Whereas THg was related to total and terrestrial pools of dissolved organic carbon (DOC), MeHgwas weakly related to DOC but strongly linked to surface concentrations of CO2, as well as toconcentrations of iron and manganese. The latter are proxies of cumulative organic matter processing withinthe network, presumably in anoxic portions of shallow bays, deep reservoir waters, and river sediments,as well as in prior seasons (e.g., under ice). Our results suggest that these deep boreal reservoirs acted more astransformation sites for Hg that was already present than as mobilizers of new Hg, and that under icemetabolism plays a role in MeHg production in these systems as we found strong dichotomies in MeHgpatterns between spring and summer.