Nutrients Limiting Phytoplankton Production in Ice-Covered Lake St. Clair

Nutrient enrichment experiments on ice-bound phytoplankton populations at three stations in Lake St. Clair, of the St. Lawrence Great Lakes system, showed that silica was the primary nutrient limiting phytoplankton growth and photosynthesis in the Thames River plume, in mid winter. The addition of silica at concentrations of 150 μg L^?1 or greater relieved this limitation. Phosphate appeared to be a secondary limiting factor.Stations 1 and 2 below river outlets, draining rural and urban areas, showed variable results. Trace metal limitation was observed at station 1 on February 20, trace metal and vitamin limitation at station 2 in March. Possible limitation by phosphate was occasionally evidenced.