A DRAINAGE-BASIN PERSPECTIVE OF MERCURY TRANSPORT AND BIOACCUMULATION- ONONDAGA LAKE, NEW-YORK

The watershed, by way of four tributaries, provides the principal inpu t of total Hg (Hg-T) to Onondaga Lake, an urban hypereutrophic lake (H enry et al., 1995). In general, atmospheric deposition is the primary source of Hg to the watershed in the absence of point source discharge s or mineral contributions. The majority of the Hg deposited from the atmosphere to the watershed is retained by the soils. The flux of Hg f rom the atmosphere to the watershed of Onondaga Lake is estimated at 2 0-30 mu g . m(-2). yr(-1), based on measurements of Hg deposition in u rbanized regions of the United States and Europe. Watershed specific y ield from three of the four tributaries that feed Onondaga Lake ranges from 5.3 to 7.5 mu g . m(-2). yr(-1). These watershed Hg export rates are higher than those observed for forested areas and represent appro ximately 25 percent of the estimated deposition to this urban location . The Hg-T specific yield from the fourth tributary, Ninemile Creek, w as substantially higher. This creek had the highest suspended solids l oading and receives runoff from an inactive chloralkali plant site. A summertime buildup of Hg species was observed in the hypolimnion of th is thermally stratified lake (Jacobs et al., 1995). Sediment trap coll ections indicated that particle settling facilitates the accumulation of Hg in the hypolimnion. The sources of CH3Hg to the hypolimnion incl ude tributary input and in situ bacterially mediated methylation. The impact of the entrainment of Hg-rich hypolimnetic water following fall destratification on the bioaccumulation of CH3Hg was not clear, becau se plankton CH3Hg levels were not generally higher following fall over turn. (C) 1996 Intox Press, Inc.