Phytoplankton community composition in relation to environmental conditions in urban lakes, ponds and reservoirs

grantor: University of TorontoMany taxa were recorded from the examination of phytoplankton assemblages in 27 urban waterbodies. However, relatively few taxa were reported at significant abundances across few sites, or even at low abundances across many sites. The majority of the common taxa had a wide trophic distribution. Only two groups displaying trophic affinities could be distinguished, i.e. meso-eutrophic and eu-hypereutrophic. The phytoplankton community response to increasing trophic conditions differed in deep and shallow systems. In deep sites, an increase in trophy was associated with an increase in Cyanophyta dominance, a decrease in the proportion of Chrysophyceae and small edible algae, and a decrease in the number of taxa contributing significantly to the total biovolume. In contrast, nutrient rich shallow sites were rarely dominated by Cyanophyta, and when they were, the taxonomic composition differed from nutrient rich deep sites. Cyanophyta dominance in shallow sites was related to water residence times greater than 7 to14 days. Euglenophyta were important contributors in many rapidly flushed shallow sites. Other algal groups, Cryptophyta, Bacillariophyceae, Dinophyta, and Chlorophyta showed no significant differences in relative abundance across trophic levels or in deep or shallow sites. A simple index of phytoplankton biotic integrity was effective in deep sites for monitoring year to year changes, and the effects of remedial actions. The application of the index is currently limited by a lack of understanding of the relationship between phytoplankton communities and ecosystem health, especially in shallow systems.M.Sc