| Project Title |  |
| Project
B5: Biogeochemical
cycling in the boreal forest - metal concentrations in woody tissues.
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| Research Team | |
| M.M. Savard Email: Msavard@nrcan.gc.ca and C. Bégin, M. Parent, NRCan, GSC.
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| Project Summary | |
| The combination of carbon isotopes, nutrients and heavy metals (tracers) in tree-rings constitutes a new environmental monitoring tool that can distinguish between natural and anthropogenic accumulation of metals. The carbon isotope ratios ( 13C) and nutrient concentrations in rings of polluted trees inversely co-vary and are marked by an abrupt shift right at the onset of smelter activities, whereas the increase of heavy metals due to these activities occurs 20 years later. These trends were established by investigating well dated ~120-year ring series extracted as cores at breast level in black spruce stems, and by comparing trees from the contaminated and control sites. However, the dendrogeochemical tracers have never been used to investigate the bulk composition for complete trees as it requires a quantitative assessment of the biogeochemical cycling of heavy metals. In breast-level stem samples, the carbon isotope ratios in cellulose of black spruce rings from the control site ranged between -26 and -23 l, and the heavy metals such as Cd between 0.01 and 0.03 ppm. The 13C ratios in cellulose of spruce rings from contaminated sites near Rouyn ranged from -26 to -20 l, and Cd from 0.02 to 1.05 ppm. Similar investigations for whole stem samples, at different levels along trees will estimate the bulk composition of the trees, thus the contribution of trees to the biogeochemical cycle of heavy metals can be quantified. | |