Carbon and Mercury Accumulation in Lake Sediments of Rapidly Thawing Discontinuous Permafrost Peatlands (Northwest Territories, Canada)

This research uses a paleolimnological approach to address gaps in our understanding of lakes as potential sinks for carbon and mercury released from thawing discontinuous permafrost peatlands. Sediment cores were collected from 14 small lakes in the southern Northwest Territories, and core chronologies and sediment accumulation rates established using 210Pb radioisotopes. Most lakes exhibited increases in mercury concentrations independent of organic carbon. Atomic C/N ratios indicated that the proportion of organic carbon from algal sources has also increased. The low sediment focussing factor (< 1.0) observed in the majority of the lakes suggests that small, hydrologically connected shallow lakes act as flow-through systems, which may promote the downstream transport of sediment (and associated carbon and mercury) through sub-arctic watersheds draining thawing permafrost peatlands, rather than acting primarily as carbon and mercury sinks.