Preliminary Characterization of Lakes in the Experimental Lakes Area, Northwestern Ontario, Using Diatom Occurrences in Sediments

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Abstract
Diatoms in deepwater surface sediment from 16 Experimental Lakes Area (ELA) lakes of varying size and morphometry were separated for analysis on the basis of their generally understood habitat preference into littoral and planktonic groups. The lakes were ranked in order of increasing relative abundance of littoral diatoms recovered from deepwater surface sediment. A significant correlation was found between the abundance of littoral diatoms in deepwater sediments and the morphometric variables: lake surface area (Ao), and shoreline length to lake volume (L/V), and percent littoral development in each lake. The Centrales was the dominant planktonic group in most of the ELA lakes examined. Species of Cyclotella and Melosira were the dominant diatoms in most ELA lakes. The ratio of the two planktonic groups—Araphidineae and Centrales (A/C)—calculated from sediment counts, agreed closely with the A/C ratio enumerated from 1969 phytoplankton counts in two lakes compared. Based on a lake classification scheme using values of the A/C ratio from sediment diatom counts, the majority of ELA lakes were classed as oligotrophic. Analysis of a 155-cm core from lake 240 showed little change in diatom species composition over the past 3000–4000 years. Centrales was the dominant diatom assemblage at all sediment depths. The dominant diatoms in the sediment of lake 240 and the majority of ELA lakes examined were similar to those dominant in the deepwater sediments of well-studied oligotrophic lakes in other lake districts. On the basis of calculated A/C ratios in surface sediment in several lakes at temperate latitudes, a lake trophic classification is proposed.

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