Trends in Dissolved Gaseous Mercury in the Tahquamenon River Watershed and Nearshore Waters of Whitefish Bay in the Michigan Upper Peninsula

A field study was conducted in June of 1998 to characterize the dynamics of dissolved gaseous mercury (DGM) in the TahquamenonRiver watershed and nearshore waters of Whitefish Bay in the Upper Michigan Peninsula. We found that over a transect acrossthe watershed, DGM levels increased generally from a creek (mean = ～12 pg L^-1), passing through the watershed, to the nearshore surface waters of the bay (mean = ～29 pg L^-1). DGM levels in nearshore surface waters of the bayranged from ～15 to ～50 pg L^-1 and peaked generally around noontime, exhibiting diurnal trends. A significant DGM decline from ～32 pg L^-1 in the early morning to ～15 pg L^-1 during the day was observed in these surface waters following passage of a coldfront, probably caused by wind-induced mixing and decrease insolar radiation associated with the frontal passage.