Research project description
Mercury biogeochemistry, fate and impact in permafrost thaw subarctic ecosystems
Introduction
The increase in the global surface air temperature is having its greatest impact in the Arctic, leading to rapid permafrost thaw and consequent mobilization of contaminants, such as mercury (Hg), that were previously locked in the permafrost. The few Hg published permafrost studies have shown that Hg methylation in permafrost soils increases with temperature, and that permafrost thaw lakes provide ideal conditions for the production of methylmercury (MMHg) by biotic Hg methylation. This doctoral project aims to: quantify Hg methylation and MMHg demethylation rates in permafrost thaw lake sediments and water; quantify Hg, MMHg and Hg(0) fluxes across sediment/water and water/atmosphere interfaces; determine Hg stable isotope fractionation in permafrost systems; as well as assess the impact of permafrost thaw on Hg release and impact on wildlife and Indigenous populations.
Objectives
This PhD project addresses the following question: How does subarctic permafrost degradation contribute to Hg release and how does this thaw process control its speciation, partitioning and fate?
The following objectives are proposed:
Obj1) To quantify Hg methylation and MMHg demethylation rates in permafrost thaw lake sediments and water and identify the controlling biotic and abiotic factors;
Obj2) To assess the biological and abiotic processes responsible for Hg reduction and oxidation in thaw lakes and their influence on the mercury (and methylmercury) pool;
Obj3) To quantify Hg, MMHg and Hg(0) fluxes across the sediment/water and water/atmosphere interfaces;
Obj4) To determine Hg stable isotope ratios in permafrost systems and explore the possibility of using Hg isotope ratios as source tracers for hydrological and atmospheric transport;
Obj5) To sssess the impact of permafrost thaw on Hg release and predict its impact on wildlife and Indigenous populations.
Study Sites
Two sites were chosen for this working plan, both in Nunavik, Canada: the Sasapimakwananisikw River Valley (SAS) in the Kuujjuarapik/Whapmagoostui area and the George River Valley in the Kangiqsualujjuaq area. While SAS is in a sporadic permafrost area, Kangiqsualujjuaq is in a discontinuous permafrost zone. Both sites have experienced high rates of permafrost degradation over the last two decades and are locations of abundant permafrost thaw lakes and ponds, the model used in this PhD project.
Material and methods
The methodology for this research project includes four topics:
T1 – Hg methylation/demethylation rates:
Sampling incubations with 199Hg and MM201Hg enriched spikes and amendment experiments;
Measurements of THg and MMHg by CV/GC-ICPMS;
Characterization of the genetic potential for the biotic mercury pathways and the involved prokaryotic groups.
T2 – Fluxes of Hg, MMHg and Hg(0):
Measurements of DGM and water/atmosphere mercury gas exchange fluxes;
Water collection at several depths and analyses for THg and MMHg.
T3 – Hg stable isotope ratios:
Collection of bottom sediments and water from the middle of the water column;
Digestion or preconcentration;
Analyzes by CV-MC-ICPMS.
T4 – Impact on wildlife and Indigenous population:
Species exposure to lake water from both sites in water tanks, oxygenated and exposed to light;
Analyzes of the ecotoxicology effect of lake water exposure on the organisms;
Modelling of the chosen species based on DEB theory.
Expected results
The results from this research will provide important information to the scientific community and decision makers to evaluate the importance of thawing permafrost on the Hg release into the arctic environment, and consequently globally. The results will also provide scientific information to local environmental management and risk assessment authorities to better manage local water and food resources. The scientific results obtained will also contribute to a better understanding of the global mercury cycle and may provide a scientific-based knowledge that would benefit the Minamata Convention and the Arctic Monitoring and Assessment Program.
Research Site Coordinates
