DIATOM ASSEMBLAGES AND THEIR RELATIONSHIP TO ENVIRONMENTAL VARIABLES IN LAKES FROM THE BOREAL FOREST-TUNDRA ECOTONE NEAR YELLOWKNIFE, NORTHWEST-TERRITORIES, CANADA

The relationship between diatom (Bacillariophyceae) taxa preserved in surface lake sediments and measured limnological and environmental var iables in 22 lakes near Yellowknife (N.W.T.) was explored using multiv ariate statistical methods. The study sites are distributed along a la titudinal gradient that includes a strong vegetational gradient of bor eal forests in the south to arctic tundra conditions in the north. Can onical correspondence analysis (CCA) revealed that lakewater concentra tions of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) each accounted for independent and statistically significant pr oportions of variation in the distribution of diatom taxa. Weighted-av eraging (WA) models were developed to infer DIC and DOC from the relat ive abundances of the 76 most common diatom taxa. These models can now be used to infer past DIC and DOC concentrations from diatom assembla ges preserved in sediment cores of lakes in the Yellowknife area, whic h may provide quantitative estimates of changes in lakewater chemistry related to past vegetational shifts at treeline.