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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From 3 to 6 November 2002, a colloquium was convened at the Benthos Laboratory of the Stazione Zoologica Anton Dohrn on Ischia, Italy, with the goal of evaluating the present status of the effects of diatoms on their main consumers, planktonic copepods, and to develop future research strategies to enhance our understanding of such interactions. These included (1) toxic effects of diatom metabolites on copepods, particularly reproduction, and (2) nutritional effects of diatoms on juvenile to adult copepods. Key issues involved in the impact of diatoms on the dynamics of natural plankton communities in situ were also addressed. During the plenary session, the most recent advances on this topic were presented. The plenary session was followed by 3 working groups on (1) production of aldehydes by phytoplankton, (2) toxic and nutritional effects of diatoms on zooplankton, and (3) the chemistry of diatom defense, as well as of their nutritional quality. These working groups focused on suggesting future research needs for the different topics. As a result, several recommendations were outlined, including experimental studies. It became evident that interdisciplinary efforts are needed, involving chemists, oceanographers and experimentalists, since many of the biological observations under controlled conditions and in situ require an integrated approach, including chemical causation. Extensive field observations based on common protocols are also recommended for investigation of the intrinsic variability of such effects and their environmental controls. Laboratory experiments are seen to be essential for the full understanding of environmentally occurring processes.

The influence of suspended sediments on the Lake Michigan ecosystem was examined using a 3-dimensional (3-D) coupled biological and physical model developed by Chen et al. (part I). The model was driven by the realistic meteorological forces observed in March 1998, with daily inputs of suspended sediment concentration that were derived from temporally and spatially interpolated satellite imagery. The model results show the significant impact of a seasonally recurring coastal resuspension plume on the spatial and temporal variation of the nutrients and plankton in southern Lake Michigan. The plume-released nutrients played an essential role in maintaining the nutrient level in the lake. Although the growth of phytoplankton in the plume depended on the availability of nutrients and light, the offshore decrease in phytoplankton biomass still satisfied the Sverdrup's relationship. Cross-shore fluxes of nutrients and phytoplankton were controlled by episodic wind events with a period of : 5 -7 days: offshore during southward winds and onshore during northward winds. The flux estimates for biological variables suggest that the microbial food web is a key contributor to secondary production in southern Lake Michigan and the lower trophic level food web system could be dynamically divided into two decoupled loops: (1) detritus-bacteria-microzooplankton-large zooplankton; and (2) nutrient-phytoplankton-detritus. The model-predicted spatial distributions of nutrients and phytoplankton were in reasonable agreement with observations taken during the 1998 EEGLE interdisciplinary cruises, suggesting that the model was sufficiently robust to capture the basic characteristics of the Lake Michigan ecosystem during the plume event.

[1] As part of the Episodic Events Great Lakes Experiment, we sampled total suspended matter (TSM), light climate, nutrients, and plankton along cross-margin transects in southern Lake Michigan during February, March, and April 1998-2000 to capture conditions before, during, and after the occurrence of storm-driven recurrent coastal sediment plumes to define the anatomy of the resuspension events and get insights into their interactions with nutrients and plankton. Variability in timing and strength of winter storms among years led to different timing, intensity, and extent of plumes among years. TSM concentrations in the core of plumes varied between 15 and 30 mg L À1 , and photic depth was reduced to $1 to 2 m, thus potentially seriously limiting phytoplankton growth in plume areas. Total P concentration was highly correlated with TSM and river influence. Chlorophyll concentrations were lower in plume regions than in adjacent areas, in contrast to the relatively constant chlorophyll concentration across the plume predicted by a coupled hydrodynamic and nutrient-phytoplankton-zooplankton model. Contrary to expectation, protozoan microzooplankton (MZ) biomass was not more abundant in the plume than adjacent waters, but was highest in nearshore areas receiving river inflow. Storms affected horizontal distribution of zooplankton. Because of the lower concentrations of phytoplankton in the plume, the plume over the short term had a negative impact on zooplankton during this food-limiting season. Our results combined with those of other EEGLE studies lead us to conclude that storms and storm-driven plumes had a negative effect on the planktonic food web. Citation: Vanderploeg, H. A., et al. (2007), Anatomy of the recurrent coastal sediment plume in Lake Michigan and its impacts on light climate, nutrients, and plankton,