Recent and fossil diatom assemblages from lakes in central and northern Alberta: Ecological and palaeoecological inferences

Assemblages of diatom species (Bacillariophyceae) were analyzed from modern and fossil sediments taken from lakes located in central to northern Alberta. Ecological and palaeoecological inferences were made from the association of species in the samples. Diatom analysis from a long sediment core ca. 8200 years taken from Otasan Lake (northeast Alberta) indicated that warmer than modern climate influenced the lake by increasing diatom productivity between ca. 7300 to 5000 years BP. Peatland formation in the catchment then influenced the lake between ca. 5000 to 3100 years BP by lowering the pH, after which the acidity decreased slightly. Diatom analysis from a long sediment core taken from Mariana Lake (northeast Alberta) indicated that the response to a warmer thin modern climate (between ca. 7500 to 5500 years BP) occurred in three stages. Initially the lake was unproductive, then water levels decreased and the lake became shallow. Finally, the lake was very turbid, eutrophic and had very high diatom populations between ca. 4300 to 2700 years BP, interpreted as a delayed response to the warmer climate.;The modern assemblages of diatom species in the surficial sediments of 93 lakes located in northern to central Alberta was examined. Water depth and concentrations of magnesium, bicarbonate and total phosphorus (TP) significantly influenced the distribution of diatom species. A model was developed to infer concentration of TP in lake water, based on sedimentary assemblages of diatom species. The correlation between observed and diatom-inferred TP concentration, using weighted-averaging unimodal statistics, was high and significant (r 2 = 0.80; p ≤ 0.05). This model was applied to the fossil sedimentary diatom record retrieved from seven lakes in Alberta. This model can be used to infer lake water TP concentration between 4 to 87 mug TP/l. Most of the fossil assemblages were statistically (p ≤ 0.05) similar to the modern assemblages. Inferences of TP concentration for those samples were accepted. Two common limitations of the model were poor correlation between benthic species and TP concentration of epilemnetic water and fossil species outside of the range of modern species (as relative percent abundance). The model can be used to estimate natural variations of TP concentration within lakes, and thus may be of use in lake management strategies.