PDFArticle Abstract
A central question addressed by the Episodic Events in the Great Lakes Experiment (EEGLE) was the extent to which the spring phytoplankton bloom in southern Lake Michigan is influenced by a recurrent coastal turbidity plume that results from wind-driven sediment resuspension and transport. Findings from a series of studies conducted as part of EEGLE during spring in 1998, 1999, and 2000 confirmed the importance of sediment processes as a factor influencing ecosystem productivity in southeastern Lake Michigan, but also identified interannual variability in river discharge as potentially important in regulating productivity in coastal waters. Here, we describe the application of satellite-derived and in situ optical observations to examine the impacts of the recurrent coastal turbidity plume (RCP) on light availability and phytoplankton productivity. A review and synthesis of prior work highlighted findings that sediment resuspension during the 1998 El Niño period, a time of intense winter storm activity and an unusually strong RCP, profoundly influenced optical properties in coastal waters, constraining phytoplankton growth and primary production. In contrast, in 1999, a moderate RCP coupled with relatively high discharge from the St. Joseph River led to a strong inner shelf optical signature indicative of elevated levels of dissolved organic matter and apparent enhancement of productivity. We speculate that future changes in climate are likely to alter sediment dynamics and river discharge with uncertain consequences for coastal ecosystem productivity and community structure in southeastern Lake Michigan as well as in other coastal systems.