Historical interrelated variations of mercury and aquatic organic matter in lake sediment cores from a subArctic lake in Yukon, Canada: further evidence toward the algal-mercury scavenging hypothesis.

This study investigates the role of climate-driven aquatic productivity increases in conrolling the sedimentary accumulation of mercury (Hg) in Kusawa Lake, Yukon, Canada. Organic geochemistry data reveals a significant link between the increasing trends of Hg and of labile algal-derived organic matter (OM) over the centuries and in particular over recent decades. Sedimentary Hg accumulation rates continue to increase even though atmospheric concentrations of Hg have remained the same or even declined. Together, these findings indicate that the significant rise in Hg content recorded in the sediments since the early 1950s may not be representative of increasing atmospheric Hg levels but are strongly influenced by elevated concentrations of algal-derived OM in the water-column. These likely increase the scavenging rate of "available" Hg from the water column. Therefore, recent increases in algal productivity may result in overestimation of the historical rates of atmospheric Hg deposition recorded in the sediments. This study confirms earlier published findings from two High Arctic lakes, and shows that the Hg-OM scavenging hypothesis may also apply to sub-Arctic lakes.