Effects of light, temperature and habitat quality on meroplanktonic diatom rejuvenation in Lake Erie: Implications for seasonal hypoxia

Rapid sedimentation of phytoplankton cells following seasonal blooms is common in lakes and coastal zones throughout the world, yet the fate of these cells is uncertain. Ascertaining the fate of seasonal blooms may be particularly important in ecosystems that experience hypoxia. Benthic stations were sampled seasonally inside and outside of the hypoxic area in Lake Erie to test for differences in chlorophyll a concentrations, algal physiological condition (cell viability) and diatom rejuvenation rates (from enclosure experiments). Hypoxic areas did sustain higher chlorophyll a concentrations compared with oxic sites; however, diatom growth and physiological capability did not differ significantly. Hypoxic areas exhibited exponential growth rates as high as 0.56 day^-1 (compared with the oxic station at 0.53 day^-1, P = 0.000) and chlorophyll rejuvenation rates as high as 0.30 day^-1 (compared with the oxic station at 0.36 day^-1, P = 0.964). Therefore, sedimentation of phytoplankton cells may not only contribute to the seasonal hypoxia observed in Lake Erie, but those diatoms able to withstand low oxygen concentrations during the summer, once reintroduced into the water column, may also seed subsequent diatom blooms. Initial estimates indicate that the algal pigment present on the bottom of the central basin, likely sedimented from the overlying water, contributed significantly to hypolimnetic oxygen depletion (11-33).