INTRODUCTION

Hydroelectric power generation has been a widely used method in Canada due to the impression that there are few associated negative environmental effects. Recent studies have shown, however, that newly-formed reservoirs are important sources of methyl mercury (MeHg) to the aquatic food web and greenhouse gases to the atmosphere (Kelly et al., 1997; Duchemin et al., 1995; Bodaly et al., 1997). As incentives to increase hydroelectric power generation grow, there is a concurrent need to improve and constrain our understanding of processes controlling the production, mobilization, and fate of MeHg.

The principal vector for MeHg exposure for humans is the consumption of fish, which may contain six orders of magnitude more Hg than surrounding waters due to bioaccumulation. The toxicity of MeHg is well documented, and targets the development of the fetal central nervous system in humans.

The production of MeHg is due to the decomposition of newly-flooded organic matter in peat, soil and vegetation, which greatly enhances the activity of microbes (including that of sulfate reducing bacteria, which are most often linked to mediating MeHg production). Thus, vegetation and soil carbon storage is an important consideration in the creation of hydroelectric reservoirs.

A recent study was conducted to examine the Hg dynamics in a flooded wetland at the Experimental Lakes Area, Kenora, Ontario, Canada (ELA; Kelly et al., 1997), which quantified concentrations and fluxes of total and methyl Hg from the soils. This follow-up study attempts to quantify similar measurements in impoundments of varying soil organic matter content, in order to establish its relationship to Hg mobilization, methylation, and incorporation into the food web.

The objectives of our group are to characterize the importance of Hg mobilization from soils of varying organic matter content (including a pre-flood soil description) at three upland forest sites within ELA, and to quantify the flux and speciation of Hg over time subsequent to the flooding event. Such data is imperative in linking reservoir creation with effects on Hg concentrations in fish. We are working closely with other groups on this project, including those examining complimentary subjects such as atmospheric deposition, Hg mobilization from litter/vegetation, food web dynamics, and soil carbon isotopes/decomposition.

SITE DESCRIPTION

Wooden dikes and earthen berms have been constructed in order to flood the desired topography, which will range in depth from 1-3 m. Water will be supplied by pumps from nearby Roddy Lake, which will maintain a steady-state flow through each enclosure. Flooding will commence June 1999, and is expected to last 3 years.

Three upland jackpine forest sites (0.8 ha) have been selected at ELA in order to provide a range of soil organic matter and moisture:

Site 1 is moderately wooded and is the wettest; its soils are composed of rich, organic topsoils of mosses and pine needles

Site 2 is densely wooded and is drier than Site 1; its soils are predominantly pine needle topsoils

Site 3 is patchy forest, and is the driest site; open areas consist of exposed bedrock covered by lichens and mosses

Bodaly, R.A, V.L. St. Louis, M.J. Paterson, R.J.P. Fudge, B.D. Hall, D.M. Rosenberg, and J.W.M. Rudd (1997). Bioaccumulation of mercury in the aquatic food chain in newly flooded areas. In Mercury and its Effects on Environment and Biology (H. Sigel and A. Sigel, eds.), Marcel Decker, New York, pp. 259-287.

Duchemin, E., M. Lucotte, R. Canuel, and A. Chamberland (1995). Glob. Biogeochem. Cycles 9: 529.