Methyl mercury production and loss in Arctic soil

Area of Science:

• Environmental Science
• Geochemistry
• Arctic Ecology

Background:

• Mercury contamination in Arctic predators poses risks to indigenous populations.
• Atmospheric mercury cycling is well-studied, but terrestrial ecosystem cycling remains unclear.
• Understanding mercury's fate in Arctic soils is crucial for assessing ecosystem and human health risks.

Purpose of the Study:

• To investigate whether wet sedge meadow soils in the Arctic act as sources or sinks for methylmercury (MeHg).
• To assess the potential for mercury methylation in Arctic soils.
• To explore factors influencing MeHg concentrations and spatial variability in these ecosystems.

Main Methods:

• Field measurements of MeHg concentrations and biophysical parameters in wet sedge meadows over a 19-day period.
• Soil microcosm experiments to assess mercury methylation potential using HgCl2.
• Analysis of dominant ligands (dissolved organic matter, sulfide) and mercury speciation.

Main Results:

• Soil MeHg concentrations showed a net loss over the summer sampling period.
• Dissolved organic matter was the dominant ligand; sulfide was low, suggesting limited methylation potential during summer.
• Soil microcosms demonstrated the capacity for mercury methylation, indicating potential exists.
• Significant spatial variability in MeHg concentrations was observed, not explained by measured biophysical parameters.

Conclusions:

• Arctic wet sedge meadow soils likely act as sinks rather than sources of MeHg during the summer.
• Mercury methylation may predominantly occur during the spring snowmelt period.
• Geochemical variability in meltwater is a probable driver for observed spatial MeHg variations in soils.