Dynamics of Lake Michigan Phytoplankton; Relationship to Nitrogen and Silica Fluxes

We describe rates of nitrogen and silica concentration change during May–August 1983 and 1984 in southeastern Lake Michigan and compare those rates with measured plankton processes. Epilimnetic dissolved inorganic nitrogen depletion, compared with total phytoplankton demand, suggests that about 44% of the nitrogen demand is recycled. Epilimnetic diatom production, calculated from soluble silica depletion, is a relatively small fraction (< 20%) of total primary production, even when diatoms dominate. Sedimentation of epilimnetic diatom silica, compared with total silica depletion, suggests that a large portion (approximately 43%) of epilimnetic particulate silica sedimentation is due to nonliving diatoms.