JULIUS, M.L. Department of Biological Sciences, St. Cloud State University, St. Cloud, MN. - Relationship between periodic resuspension events and planktonic diatom community structure in Lake Michigan: a field and laboratory investigation.
Lake Michigan provides an ideal location for comparing episodic
physical forcing events (storms) on phytoplankton processes and the
more persistent seasonal variability of phytoplankton communities.
This is due to the duration and extent of the highly turbid, recurrent
coastal plume (RCP) in the lake during the winter/ early spring.
Although the RCP can coincide with the initiation of the basin wide
spring diatom bloom, linkages between the duration and intensity of
the plume and the prominent role of light availability in regulating
Lake Michigan phytoplankton growth during the spring isothermal period
have been postulated, but not verified. The concurrent physical and
biological events provide a novel opportunity to examine phenomena
associated with the RCP affecting the distribution and abundance of
species in Lake Michigan's planktonic diatom flora. In this study,
planktonic diatom assemblages from pre, post and active spring plume
events were examined from stations along Lake Michigan’s southern
shoreline. Species abundance changed rapidly during storm events.
Sediment resuspension via storm activity created a sub-optimal growth
environment. Post-storm event diatom phytoplankton communities were
floristically distinct from pre-storm event communities, with resting
cell-forming taxa playing a significant role in these
community-restructuring periods. Laboratory simulations of
resuspension events using Lake Michigan sediments were conducted under
a variety of environmental conditions. Parameters varied included day
length, temperature, and silica. The resulting assemblages were
quantitatively counted. A statistically significant relationship was
identified between day length and the vegetative growth of many
resting cell-forming diatom species. When day length was calculated
for post-storm event field data, it revealed a high correlation
between post-storm event communities and those predicted by the
laboratory simulations. Timing of storm events and latitudinal
position of the aquatic system are then important elements for
consideration when predicting diatom phytoplankton community structure
due to the relationship these factors have with day length.
Key words: coastal plume, diatoms, resting cells, sediment resuspension