Effects of silicate depletion on photosynthesis by diatoms in the plume of the Hudson River

Silicate depletion was observed during a bloom of netplankton diatoms. Netplankton chlorophyll a increased over the same salinity range and at the same rate that silicate decreased. Silicate depletion coincided with a decrease in the apparent Si:N uptake ratio as well as a change in the magnitude and diurnal phasing of light saturated photosynthesis (P _m ^B ) by netplankton diatoms. Nanoplankton P _m ^B was unaffected by silicate depletion and increased with temperature. Consequently, nanoplankton P _m ^B eventually exceeded netplankton P _m ^B while netplankton biomass was still increasing relative to nanoplankton biomass.