The structure and composition of epilithic diatom communities of the St. Lawrence and Ottawa rivers in the Montreal area

Abstract

The structure and composition of epilithic diatom communities were studied at five stations in the St. Lawrence River and one station in the Ottawa River, adjacent to the south shore of the island of Montreal. The diatom flora was composed of 139 species and varieties of Bacillariophyceae. The species composition generally reflected a eutrophic and organically polluted environment. The structure of the diatom communities of the Ottawa River (station I) and of the St. Lawrence River upstream (station II) and downstream along the south shore of the island of Montreal (stations III and IV) was similar with respect to total number of species (41–44 species), diversity (species richness (d): 3.01–3.88 and Shannon-Weiner information measure of diversity [Formula: see text]: 2.01–3.34), and biomass (463.9–1656.0 μm3/mm2). Further downstream station V had fewer species (12 species) and a significantly (P < 0.05) lower diversity (species richness d: 1.87 and Shannon-Weiner information measure of diversity [Formula: see text]: 0.35). The station below it (station VI) had a significantly (P < 0.05) lower biomass (51.2 μm3/mm2) and a lower density (68 cells/mm2). The structure and composition of the diatom communities at the different stations are discussed in relation to environmental factors.