Contrary to expectations of fairly uniform and unstratified waters, sea-viewing wide field-of-view sensor (SeaWiFS) and moderate-resolution imaging spectroradiometer (MODIS) imagery revealed a

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A coupled physical and biological model was developed for Lake Michigan. The physical model was the Princeton ocean model (POM) driven directly by observed winds and net surface heat flux. The biological model was an eight-component, phosphorus-limited, lower trophic level food web model, which included phosphate and silicate for nutrients, diatoms and non-diatoms for dominant phytoplankton species, copepods and protozoa for dominant zooplankton species, bacteria and detritus. Driven by observed meteorological forcings, a 1-D modeling experiment showed a controlling of physical processes on the seasonal variation of biological variables in Lake Michigan: diatoms grew significantly in the subsurface region in early summer as stratification developed and then decayed rapidly in the surface mixed layer when silicate supplied from the deep stratified region was reduced as a result of the formation of the thermocline. The non-diatoms subsequently grew in mid and late summer under a limited-phosphate environment and then declined in the fall and winter as a result of the nutrient consumption in the upper eutrophic layer, limitation of nutrients supplied from the deep region and meteorological cooling and wind mixing. The flux estimates suggested that the microbial loop had a significant contribution in the growth of microzooplankton and hence, to the lower-trophic level food web system. The model results agreed with observations, suggesting that the

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[1] The impact of a reflective, recurrent coastal resuspension plume on the lower trophic food web system in Lake Michigan was examined using a 3-D coupled physical and biological model. Numerical experiments were conducted for the March 1998 and 1999 plume events. The comparison between modeling results of these 2 years shows that the spatial distributions of the biological fields (i.e., phosphorus, phytoplankton, detritus, etc.) were closely coupled to the physical environment associated with wind-induced threedimensional circulation and mixing. The influence of suspended sediment plumes on the lake ecosystem was reflected in heterotrophic (secondary) production rather than in the autotrophic (primary) production. Nutrients were maintained through nutrient release from suspended sediments within the plume, while it was supplied by current advection and diffusion in the interior. The cross-shore flux of nutrients was driven by episodic wind events with a period of about 5-7 days. The flux was offshore during northerly winds and onshore during southerly winds. Comparisons between energy fluxes among biological variables suggest that the microbial loop (detritus-heterotrophic bacteria and microzooplankton) played an important role in the ecosystem dynamics during plume events. Bacteria were good competitors with phytoplankton for inorganic phosphorus and were also a key supporter for growth of microzooplankton inside and outside the plume. As a result, the lower food web system could be divided into two decoupled loops: (1) detritus-bacteria-microzooplankton-large zooplankton and (2) nutrient-phytoplanktondetritus.