RESUMO
The mercury cycle in seven northern Wisconsin seepage lakes was characterized by high atmospheric influx, removal by sedimentation and evasive efflux, and by in-lake transformation of Hg to biologically sequestered methyl Hg species. Direct depositional Hg loading from lhe atmosphere to lakes was roughly lO ug/m2/year, with rain and snow Lhe principal delivery vectors. Annual atmospheric Hg deposition exceeded estimated fish bioaccumulation by a factor of roughly 10. The atmospheric Hg inffux was roughly balanced by losses to sediments and the return of volatile Hg° to the atmosphere. The relative importance of sedimentation and gaseous evasion as Hg loss terms varied from lake to with sedimentationl/evasion ratios ranging from 9:1 to 1:1 in the seven lakes studied. Residence times for Hg varied from roughly 125 to 300 days in these lakes. Methyl-Hg in these lakes also had an atmospheric source, estimated to he roughly 1% of the total Hg inputs. Although the direct atmospheric deposition and sediment accumulation of methy-Hg was miuch lower than annual rates of methy-Hg bioaccumalation...