Effects of resuspension events on restructuring
phytoplankton communities
PIs: Linda M. Goad and Matthew L. Julius
Objectives:
- Identify the species composition of plume event phytoplankton floras.
- Note floristic differences between spring and fall plume floras as well
as assemblage composition outside of the plume.
- Isolate abiotic and biotic variables effecting species composition in plume floras.
Approach:
- Sampling was performed before and after plume events in the spring, summer and
fall along transects in southern Lake Michigan. (baseline)
- In plume and out of plume phytoplankton sampling was performed along southern
Lake Michigan transects during plume events. (effect)
- A series of short sediment cores were taken at the southern Lake Michigan stations.
This sediment material was resuspended in the laboratory under varying light,
temperature, and nutrient conditions to simulate plume conditions. (cause)
Results:
Pre-plume spring phytoplankton floras can be generalized as follows:
- Phytoplankton numbers are relatively high, but species diversity is
relatively low.
- Diatoms dominate species composition.
- Diatom species generally include delicate chain forming taxa, i.e.
Cyclotella michiganiana, Cyclotella ocellata, Fragilaria capucina, and Tabellaria
fenestrata
Plume event phytoplankton floras can be generalized as follows:
- Phytoplankton numbers are relatively low, but species diversity is relatively high
(caused by the number of benthic and other taxa reintroduced to the water column).
- Diatoms dominate species composition.
- Taxa are most frequently resting cell forming species, which are rapidly expanding
and dividing. Aulacoseira islandica and A. italica are the most common,
with
Fragilaria crotonensis, Stephanodiscus minutulus, S. subtransylvanicus, and
S. alpinus being the subdominant.
The pre-plume flora generally replaces the plume flora within 2 weeks of the plume
events conclusion.
Sediment resuspension experiments in the laboratory indicate time may be the single
most important factor. Aulacoseira islandica and A. italica always dominate the species
composition in the initial phase of the resuspension experiment, regardless of
modifications in light, temperature, and nutrients. Once the initial Aulacoseira spp.
pulse has diminished, other species being increasingly abundant varying in relation
predominately to differing light and temperature regimes.