A Lakewide Study of Phytoplankton Biomass and its Species Composition in Lake Erie, April–December 1970

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Abstract
Surface samples of phytoplankton were collected from April-Dec. 1970 at approximately 4 wk intervals from 25 stations distributed over the entire lake [Canada, USA]. Taxonomic identification and enumeration was done by the Utermoehl technique. About 125-150 spp. were identified in each basin. Less common or rare species contributed significantly to the total phytoplankton biomass. The species comparison among the 3 basins indicated that species like Rhodomonas minuta and Cryptomonas erosa were perennial in all the basins. Aphanizomenon flos-aquae, Anabaena spiroides var. contracta, Coscinodiscus rothii, Actinastrum hantzschii, and Ceratium hirundinella were typical for the Western basin. Ochromonas spp. and Peridinium aciculiferum were common in the Central basin; Gymnodinium helveticum and G. uberrimum were characteristic for the Eastern basin. The diatoms contributed least in the Eastern basin (36%) but showed a high percentage in both Central (55%) and Western (58%) basins. The phytoflagellates made important contributions in the 3 basins; the highest percentage (41%) was in the Eastern basin. Phytoflagellate abundance increased from west to east and appeared to have a wide range of adaptability to different nutrient conditions. During July and Aug. high biomass concentration but uneven horizontal distribution was observed. Phytoplankton biomass ranged between 0.8-13.2, 0.6 and 6.0 and 1.0-4.2 g/m3 in the Western, Central and Eastern basins, respectively. The highest biomass of 13.2 g/m3 was in the Western basin during April. Inshore-offshore differentiation was observed in the Central and Eastern basins with many peaks in the inshore region. Size analysis of phytoplankton on a few stations showed that the nannoplankton (.ltoreq. 64 .mu.) comprised a major portion of phytoplankton biomass during spring and fall periods. Based on maximum biomass concentration, the Lake Erie Western basin was classified as highly eutrophic, the Eastern basin as mesotrophic and the Central basin between the mesotrophic and eutrophic conditions.