Fig. 1. A schematic of our terrestrial mercury (Hg) model.

The soil extends down to 15 meters with an active layer that thaws in summer and refreezes in winter. The organic carbon and Hg extend down to three meters. Hg deposits onto the surface from the atmosphere and bonds to plant and soil organic matter. As organic matter decays, elemental mercury (Hg⁰) is released into the atmosphere, some mercury cation (Hg^II) is exported into rivers, and the remaining Hg^II is recycled back into the organic matter. We use empirical relationships to estimate methyl mercury (MeHg) concentrations in water from Hg^II export and total Hg concentrations in fish from MeHg concentrations.