Physical-Biological Coupling in Southern Lake Michigan: Influence of Episodic Sediment Resuspension on Phytoplankton

The influence of episodic, sediment resuspension on phytoplankton abundance/volume and composition, the photosynthetic maximum rate (P^B _max) and efficiency (^B), and chlorophyll-specific growth (_Chl) was evaluated during the spring isothermal period in southern Lake Michigan (Laurentian Great Lakes, USA). Resuspension altered the nutrient and light climate of nearshore waters; light attenuation (K_d) and phosphorus concentrations corresponded (p 0.0001 and p 0.001, respectively) with concentrations of suspended particulate matter (SPM). Phytoplankton cell volume and diatom cell abundance and volume were not associated with SPM concentrations (p > 0.05). Diatom composition displayed spatial dissimilarities corresponding with resuspension (p 0.001); small centric diatoms exhibiting meroplanktonic life histories and pennate diatoms considered benthic in origin were most abundant within SPM-impacted, nearshore waters whereas taxa typically comprising assemblages in optically-clear, offshore waters and the basin-wide, spring bloom were not. Values of P^B _max and ^B corresponded (p 0.0001) with both K_d coefficients and SPM concentrations, potentially reflecting increased light harvesting/utilization within impacted assemblages. However, integral production was inversely associated with K_d coefficients and SPM concentrations (p < 0.0001) and photosynthesis was light-limited (or nearly so) for most assemblages. Although _Chl values corresponded with K_d coefficients (p 0.05), values were quite low (x ± S.E., 0.10 ± 0.004 d^-1) throughout the study. Most likely, distinct rate processes between SPM- and non-impacted assemblages reflected short-term compositional (and corresponding physiological) variations due to infusion of meroplankton and/or tributary-derived phytoplankton. Overall, resuspension appears to have little, if any, long-term impact upon the structure and function of the lakes phytoplankton.