Mercury air/surface exchange kinetics of background soils of the Tahquamenon River watershed in the Michigan Upper Peninsula

Air/surface exchange of mercury was investigated over background soils at f ive sites in the Tahquamenon River watershed in the Michigan Upper Peninsul a in the summer of 1998. Measurements of Hg fluxes were performed during mi dday periods using the ORNL Teflon dynamic flux chamber. Mean Hg emission f luxes were 1.4 +/-0.3-2.4 +/-1.0 ng m(-2) hr(-1) for three shaded forest si tes and 7.6 +/-1.7 ng m(-2) hr(-1) for an open field site. Hg dry depositio n was observed at a heavily shaded forest site over wet soils (mean = -0.3 +/-0.2 ng m(-2) hr(-1)). The overall mean Hg flux was 1.4 +/-1.4 ng m(-2) h r(-1) for the four shaded forest sites. The Hg fluxes observed at these sit es are similar to those found at other northern background sites. Significa nt, rapid response of Hg emission to solar radiation was observed over thes e background soils. Artificial irrigation over these soils induced immediat e and measurable increases in Hg emission. Soil temperature was found to be less influential to Hg air/surface exchange over these heavily shaded fore st background soils than we have seen elsewhere.