Phytoplankton as indicators of environmental health

Summary

Lake Ontario phytoplankton were collected during 8 cruises in the spring and summer from 1986 to 1987. By comparing the recent microfossil record with historical water column data, phytoplankton are used to evaluate trends in the trophic status of Lake Ontario. The recent microfossil record suggests that diatom species associated with grossly polluted areas have decreased, while the most recently deposited assemblages are composed of species tolerant of eutrophic conditions. The offshore lake data also indicate an improvement but suggest mesotrophic conditions rather than eutrophic conditions. Currently, mesotrophic diatom species account for 30% of the phytoplankton biomass while eutrophic diatoms represent less than 10% of the offshore phytoplankton biomass in the water column.