SECULAR VARIATIONS OF THE WATER LEVEL IN THE RIVIERE BONIFACE WATERSHED (NORTHERN QUEBEC) - A DENDROECOLOGICAL ANALYSIS

Secular variations of the water level in the Riviere Boniface watershed (northern Quebec): a dendroecological analysis. Establishment and mortality dates, and tree-ring patterns of black spruce found in lacustrine and fluvial shorelines of the Riviere Boniface watershed (northern Quebec) were used to reconstruct water-level changes since the XVlth century. The oldest period correspond to a low level during the XVlth and XVllth centuries, followed by a rising level during the first half of the XVlllth century (between 1720 and 1740). A high water level prevailed at the end of the XIXth century and culminated during the XXth century, particularly in the 1930s and 1940s. A second period of low-water level occurred at the end of the 1950s and lasted until the beginning of the 1970s. The massive expansion of black spruce during that period was associated with snowless conditions, which suggests that snow precipitation is the major factor controlling height of the water level. Our data indicate that the Little Ice Age may be subdivided into two distinct periods, i.e. the first one being drier with low water levels from the end of the XVlth century to 1720-1740, and the second period, with moister conditions, which makes the transition towards the milder XXth century. Finally, the development of cryosols in the shoreline habitat during the Little Ice Age was associated with low water levels.