Mercury dynamics and transport in two Adirondack lakes

We investigated the chemistry and fluxes of mercury (Hg) species for two Adirondack lakes with contrasting landscape, physical, and chemical attributes. Samples were collected monthly at the lake inlets and outlets over 2 yr, and evasion of elemental Hg was measured at one lake (Arbutus). Concentrations of total Hg (THg) and methyl Hg (MeHg) in watershed runoff were highly variable throughout the year, increasing markedly during summer months. The proportion of THg as MeHg ranged from <5% at Arbutus Lake up to 10% at Sunday Lake. Concentrations of Hg species increased with increases in dissolved organic carbon concentrations and percentage wetland coverage. The estimated rate of volatilization loss of elemental mercury (Hgo) from Arbutus Lake surface (7.8 μg m22 yr21) was comparable to the rate of direct atmospheric Hg deposition to the lake surface (8.6 μg m22 yr21). Dry deposition to Arbutus Lake amounted to ca. 26% of total wet THg deposition. Hydraulic residence time (HRT) played a critical role in controlling Hg dynamics in the lakes. Negligible removal of THg inputs was observed at Sunday Lake, which has a short HRT (0.02 yr), compared with approximately 60% removal at Arbutus Lake, which has a longer HRT (0.6 yr). This pattern of increasing net Hg retention in lakes with increasing HRT was consistent with other mass balance studies in the literature. Both Arbutus and Sunday lakes were net sinks of MeHg.