Assessment of Mercury and Organic Matter in Thermokarst Affected Lakes of the Mackenzie Delta Uplands, NT, Canada

• Main Author: Deison, Ramin
• Language: English
• Published: 2012
• Subjects: permafrost; thermokarst; Mackenzie Delta; Northwest Territories; Canada; Climate warming; Mercury in Thermokarst Affected Lakes; sedimentation; Organic Matter in Thermokarst Affected Lakes; Thermokarst
• Online Access: http://hdl.handle.net/10393/20645

The Mackenzie Delta region of the Northwest Territories, Canada, has experienced rapid climate warming in the past century resulting in rapidly thawing permafrost in this region. This thesis examines spatial and temporal changes to sediment organic carbon and mercury flux in lakes from thermokarst regions by comparing sediment cores from lakes with and without retrogressive thaw slumps on their shorelines. We show that sediments from lakes with permafrost thaw slump development on their shorelines (slump lakes) had higher sedimentation rates as well as lower total Hg, methyl mercury (MeHg), and labile OC fractions when compared to lakes where thaw slumps were absent. Total Hg and MeHg concentrations in sediments were correlated with total organic carbon (TOC), S2 (labile algal-derived OC), and inferred chlorophyll a content, indicating an association between autochthonous organic carbon and Hg in these sediments. Correlations between mercury and S2 in these study lakes generally support the hypothesis that algal-derived materials correlate with Hg concentration in sediments. We observed higher S2 concentrations in reference lakes than in slump lakes, likely due to uninterrupted algal production, lower dilution by flux of inorganic matter, and possibly better anoxic preservation in reference lakes compared to slump lakes. It is evident that thaw slump development in this thermokarst region increases inorganic sedimentation in lakes, while decreasing concentrations of organic carbon and associated Hg and MeHg in sediments.