Ultrastructure and seasonal growth patterns of microbial mats in a temperate climate saline-alkaline lake: Goodenough Lake, British Columbia, Canada

Abstract

Goodenough Lake is a small (ca. 1 by 0.6 km) saline-alkaline lake on the Caribou Plateau in British Columbia, Canada, which has a mean depth of < 1 m, allowing the growth of substantial prokaryote-dominated benthic microbial mats over the entire lake bottom. Microbial mats were investigated on both a detailed ultrastructural level and at a macroscopic level to determine, on a lakewide scale, the seasonally influenced changes that occurred over the course of a spring to fall growth season. The acceleration of phototrophic activity with warming of the lake water in spring could be followed by increases in dissolved oxygen levels, which quickly reached supersaturation early in the summer. The grazing activity of brine fly larvae (Ephydra hians) was found to have a significant influence on mat growth and development patterns. On an ultrastructural level, several types of filamentous cyanobacteria were the main phototrophic organisms present, even in anaerobic parts of the mats, where they were accompanied by purple bacteria. The dominant cyanobacterium present was a large oscillatoriacean form which, in certain parts of the lake, formed unusual columnar structures that had a very low diversity of microbial species in comparison to mats from other regions of the lake. The microbial community also differed in areas of the lake where less saline groundwater springs emerged from the lake bed.Key words: microbial mats, saline-alkaline lakes, cyanobacteria, ultrastructure.