Seasonal Si:C ratios in Lake Erie diatoms — Evidence of an active winter diatom community

Recent investigations of Lake Erie in the winter have demonstrated the occurrence of substantial phytoplankton communities largely consisting of the diatom Aulacoseira islandica (O. Müller) Simonsen. To assess the activity of this diatom community, multiple measures of production, both general and diatom-specific, were undertaken. We measured oxygen (O2) evolution as proxy for carbon (C)-fixation and 2-(4-pyridyl)-5-((4-(2-dimethylaminoethylaminocarbamoyl) methoxy)-phenyl)oxazole (PDMPO) incorporation as a measure of silica (Si) deposition. The latter demonstrated conclusively that diatoms were active during winter months and confirmed that diatoms are the primary drivers of winter productivity. The stoichiometric relationship between carbon and silica in the winter Lake Erie phytoplankton assemblage was further compared to the activity of the summer community. Although the winter phytoplankton community was observed to be active, it was less active than the summer community, with lower measured rates of O2 evolution and Si deposition. These findings provide a new and expanded understanding of the biological carbon production in Lake Erie.

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► Diatoms dominate the winter community in Lake Erie.
► Fluorescence assays demonstrate that most diatoms are active in the winter.
► Comparisons to summer months show a higher Si:C ratio for winter communities.
► Significant winter diatom export may help drive summer hypoxia in Lake Erie.