In Vitro Release of Mercury and Methylmercury from Flooded Organic Matter
Dominant vegetation and soil types found within the La Grande complex of northern Québec were subjected to flooding under controlled laboratory conditions of temperature, pH and levels of dissolved oxygen. For all substrates, the cumulative quantities of mercury (Hg) released showed an asymptotic behaviour as a function of time. Under the conditions set for the experiments, Hg releases to the water column occurred rapidly but were of relatively short duration (< 1 year). Of the different vegetation types, sphagnum moss (Sphagnum sp.) released the greatest amount per unit dry weight of total Hg, ~ 40 ng g-1 dry weight. Alder (Alnus sp.), lichen (Cladonia sp.) and spruce (Picea mariana) were all within the range of 4–10 ng g-1 regardless of the treatment applied. Alder released the greatest amount of methylmercury (MeHg), 5 ng g-1 representing ~ 60% of total Hg. For sphagnum moss, MeHg released 3 ng g-1, ~ 8% of total Hg. Alder and spruce were within the range of 1–2 ng g-1. Globally, there were no clear effects of temperature, pH and levels of dissolved oxygen on releases of total Hg or MeHg, although for individual substrates there were some differences. For the humus samples, feather moss (Pleurozium sp.) humus yielded greater levels of both total Hg and MeHg per unit area, ~ 45 ng m-2 and ~ 1.2 ng m-2 respectively, as compared to lichen (Cladonia sp.) humus, ~ 4.3 ng m-2 and ~ 0.35 ng m-2 respectively. For both types of humus, ambient temperature treatment always produced the highest quantities of total Hg relative to colder temperature. This was also observed in the case of feather moss humus for MeHg. The results permit estimation of the contributions of total and MeHg from the dominant vegetation and soil types of proposed reservoirs.
KeywordsWater Column Suspended Particulate Matter Cumulative Quantity Sphagnum Moss Vitro Release
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