Phytoplankton pigment distributions during the spring isothermal periods of 1998 and 1999 and their association with episodic sediment resuspension were characterized in coastal waters of southern Lake Michigan. Total and phylogenetic group chl a concentrations (derived using chemical taxonomy matrix factorization of diagnostic carotenoids) corresponded with assemblage and group biovolumes estimated from microscopic enumeration (P ≤ 0.001). Diatoms and cryptophytes dominated assemblages and together typically comprised greater than 85% of relative chl a. Total chl a concentrations and both fucoxanthin-chl a-1 and alloxanthin-chl a-1 ratios were similar across depths (P > 0.05), indicating uniform distributions of and photophysiological states for assemblages and diatoms and cryptophytes, respectively, throughout the mixed water column. Total chl a concentrations were not always spatially uniform from near-shore to offshore waters, with the greatest variability reflecting the influence of tributary inflows upon coastal assemblages. Sediment resuspension strongly influenced water column particle density and light climate; however, total and group chl a concentrations did not correspond with coefficients of Kd and suspended particulate matter concentrations (P > 0.05). The correspondence of both light attenuation and suspended particulate matter concentration with relative diatom chi a (P ≤ 0.001) indicated an apparent association between sediment resuspension and diatoms. This, and the negative association (P ≤ 0.0001) between relative diatom and cryptophyte chl a, corresponded with the spatial dominance of diatom and cryptophyte chl a in near-shore and offshore waters, respectively. The presence of viable chl a and fucoxanthin within the surficial sediment layer, established this layer as a potential source of meroplanktonic diatoms for near-shore assemblages.
- Laurentian Great Lakes