Distribution and flux of particulate mercury in four stratified seepage lakes (Chapter 1.6)
The influence of particle-mediated transport in regulating mercury (Hg) cycling in four northern Wisconsin seepage lakes was examined by analyzing total Hg (HgT) and mono methyl Hg (MeHg) in suspended and sedimenting material during 1990. Annual mean suspended particulate HgT content ranged from 0.12 to 0.68 ug g- 1 while mean MeHg content ranged from 0.047 to 0.16 ug-1. Among the study lakes, mean sedimenting flux rates for the ice-free period ranged from 126 to 305 ng m-2d- 1 for HgT and from 2.2 to 34 ng m-2d- 1 for MeHg, suggesting greater variability in MeHg than HgT fluxes. In all lakes, MeHg content of suspended particulates increased during summer stratification. Similarly, settling particles collected in sediment traps exhibited MeHg increases during this period. Upon settling, particles became depleted in MeHg relative to HgT, emphasizing, differences in cycling between these forms of Hg. Trends in particle MeHg content among lakes were also consistent with observed trends in yellow perch tissue Hg content.