Periphyton of the Experimental Lakes Area, Northwestern Ontario

Abstract

The periphyton of four Experimental Lakes Area (ELA) lakes was examined in 1969. The littoral zone of all lakes was composed chiefly of large boulders and rock shelfs and the epilithic algal assemblage was accordingly dominant. Depending directly on light penetration and substrate availability benthic algal growth in most lakes was negligible at depths greater than 10 m. Throughout the growing season diatoms were the dominant algal group within the epilithic assemblage, comprising more than 60–70% of the total algal volume. Filamentous green and blue-green algae increased in importance in July and August but never constituted more than 40% of the volume of the total algal biomass. A well-defined diatom succession was observed both on the natural lithic substrate and on glass slides. Achnangthes minutissima was the most abundant diatom encountered in the littoral zone of all lakes. Periphyton growth on glass slides in lake 240 was 27 mg organic matter/m2∙day during initial colonization and 250 mg organic matter/m2∙day during the period of maximum growth. The vertical distribution of littoral diatoms in lake 240 was examined and differences among species are discussed in light of possible regulating mechanisms. Achnanthes flexella and Eunotia pectinalis were found only in the psammonal habitat of lake 240.Statistical treatment of chemical analyses of N, P, and chlorophyll a content of periphyton showed no significant difference in amounts of total N among periphyton from lakes, but the distribution of both total P and chlorophyll a was significantly different among lakes examined. Highest concentrations of both P and chlorophyll a were found in lakes 239 and 227. In lake 227, a lake receiving weekly additions of N and P, concentrations of P were significantly greater than in the other lakes. Concentrations of N and P/unit organic weight of periphyton taken at a depth of 1 m in each of the study lakes were greatest in lake 227. Comparisons among lakes are made and, based on the results of these comparisons, the role of N and P as regulators of periphyton growth in the ELA lakes is discussed.