CGRG Bibliography of Canadian Geomorphology
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Author : Begin, C.; Savard, M.M.; Marion, J.; Gingras, M.; Smirnoff, A.; and Bégin, Y.
Date : 2008.
Title : Reconstruction of hydroclimatic conditions over the past 200 years in the James Bay hydropower region based on dendroisotopes.
Publication : Quebec 2008: 400 Years of Discoveries. Joint Meeting of the Geological Association of Canada, Mineralogical Association of Canada, Society of Economic Geologists and the Society for Geology Applied to Mineral Deposits. May 26-28, 2008. Québec City Convention Centre, Québec.
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Abstract
Sustainable management of water supply in the context of hydropower production and clean energy policies is a major concern for modern societies. Modeled climate projections may show hydrological changes out of the range of hydro-meteorological records which rarely cover more than the last 40 years in northern regions. Using such short-term records can induce an undesirable bias in forecast models. Thus, a multidisciplinary study has been initiated in the area producing most hydropower for Québec. Our aim was to reconstruct quantitatively the main variables used in hydrologic forecast models using several tree-ring indicators (ring width, density and stable isotope ratios). The main climate variables are summer temperatures, snow precipitation and seasonal water supply. The entire project is based on more than one hundred tree-ring site chronologies sensitive to various drainage conditions and distributed within an area of 320 000 km2 (800 km in longitude x 400 km in latitude). Results presented here specifically concern stable isotope ratios (d13C and d18O) in tree-ring series from three old-growth black spruce stands representative of the upstream sector of the La Grande River basin (Hurault Lake, DA-1 and Pool sites). The high potential for reconstruction using the isotopic indicators mainly relates to the direct influence of climatic factors on physiological processes controlling the isotopic fractionation, notably stomatal functions. All series cover the 1800-2004 period; bi-annual analyses were performed for the older part of the series (1800-1940) whereas the recent part (1941-2004) was analyzed with an annual resolution to compare the dendroisotopic results with measured hydro-climatic variables. Statistical tests used to unravel the climatic significance of mean isotopic ratios show that d18O values mainly directly reflect summer temperatures (r=0.65) but also correlate negatively with water inflow during the July-November period (r=-0.64). On other hand, d13C values correlate with a summer climatic index (r=-0.61), integrating temperature and precipitation effects. We also show that combining d18O and d13C values increases correlations with several climatic parameters. Multiple regression models coupled with a bootstrap verification procedure were then applied to isotopic data to reconstruct targeted hydroclimatic variables over the last 200 years. The reliability of the reconstructed series was finally established by comparing our results with independent published data from the same region. At this stage of the research program, our results clearly confirm the high potential of dendroisotopes as valuable proxies of past hydroclimatic conditions.
Bibliography of Canadian Geomorphology