CGRG Bibliography of Canadian Geomorphology
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Author : Grenier, A.; and Gajewski, K.
Date : 2000.
Title : Comparison of lake-sediment chemistry and pollen analysis at treeline in northern Québec.
Publication : GeoCanada 2000. Calgary, Alberta. May 29-June 2, 2000.
Issue : Abstract
Page(s) :
Abstract
One goal of pollen analysis is to document the arrival of a plant taxon to an area. In the region of treeline, the arrival or disappearance of spruce is of interest for paleoecological or paleoclimatic reconstructions. However, pollen are transported by several mechanisms, including by wind, streams and insects, and some pollen are transported far from the source plant. Although pollen can be used to document the presence of a taxon on regional scales, at a site level it is sometimes difficult to determine the arrival of a species in the immediate area of a lake from the fossil pollen. The arrival of spruce in the watershed should be recorded in the lake sediment chemistry. Conifer species tend to acidify the soil. The acidification of the soil should influence the water in streams and lakes, thus influencing mobility of some elements in the lake water column. Thus, the presence of spruce should be recorded in lake-sediment chemistry. This study was conducted in the area of the Rivière Boniface in northern Québec. Lake-sediment cores were raised from two sites 15 km apart. The region surrounding site RB6 is currently forested, whereas lake RB23 is near the tree limit. A pollen diagram from RB6 shows that spruce arrived in the region around 3000 years ago, with maximum percentages around 2500 yr BP. Picea pollen percentages from RB23 are typically less than 10%. Spruce pollen increased around 2200 years ago but values remained less than 20%, suggesting spruce was never present around this site. Lake-sediment chemistry was analysed using the method of Engstrom and Wright (1984), that extracts the major elements in three steps. The first consists of extracting the elements that are soluble in HCl. The second step extracts the Biogenic Silica using NaOH. In the last step, the residue remaining after steps 1 and 2 are fused and put into solution. Major elements were analysed using emission spectroscopy ICP. There is a strong correlation in RB6 between the HCl soluble Fe, Mn, and Picea pollen percentages and to a lesser extent, Biogenic Silica. This suggests that the arrival of spruce in the watershed affected the water chemistry of the lake. This effect on the lake ecosystem was significant enough to influence the aquatic biological productivity.
Bibliography of Canadian Geomorphology