Mercury Dynamics in Sub-Arctic Lake Sediments Across a Methane Ebullition Gradient

• Main Author: Erickson, Lance
• Format: Text
• Language: English
• Published: 2014
• Subjects: Abisko; Arctic; Arctic Lake; Stordalen; permafrost
• Online Access: http://archives.gac.edu/cdm/ref/collection/irstudents/id/3451

Recent studies have suggested that Arctic warming may play a key role in enhancing carbon (C) and mercury (Hg) export from permafrost peatlands, yet the mechanisms by which Hg is mobilized during thaw remain enigmatic. To elucidate the links between these chemical systems, we investigated Hg concentrations in cores taken in organic C rich sediments in Lake Villasjön (avg. depth 1.5m) at the Stordalen Mire, Abisko, Sweden. We chose coring sites based on zones with significantly different ebullitive methane (CH4) fluxes established in earlier studies and we hypothesized that the microbial community producing CH4 is also potentially mobilizing Hg. Four recovered sediment cores (39-44cm long) were characterized by having roughly 30cm of organic-rich silt material on top of a transition to more clastic material in the bottom ~10cm. Cores were sub-sampled every 2cm, and the sediment samples were then freeze-dried. Sub-samples were analyzed for extractable Hg by cold vapor inductively coupled plasma mass spectrometry (2 cores) and for total Hg by thermal decomposition and cold vapor atomic fluorescence (2 cores). Mercury was most abundant in the upper portions of all sediment cores, after which concentrations decreased with depth. The highest ebullition site had Hg concentrations exceeding 80 ngHg/gsediment at the core top that decreased to a low Hg concentration < 15 ngHg/gsediment at the core base. The lowest ebullition site had overall lower concentrations compared to the higher ebullition sites with more intermediate values (< 50 ngHg/gsediment) starting at 2cm depth, dropping to < 15 ngHg/gsediment at ~ 26 cm. We found differences 3 (≥ 50%) in overall Hg contents of surficial sediments. Mercury content positively correlated with total organic C (TOC, R²=0.74) and sulfur (S, R2=0.92) in the highest ebullition site. Mercury content also negatively correlated with dissolved inorganic carbon (DIC) in the highest ebullition site (R²=0.71). These relationships are only seen in the higher ebullition sites, ...