A modeling study of benthic detritus flux's impacts on heterotrophic processes in Lake Michigan

Effects of sediment resuspension-induced benthic detrital flux on the heterotrophic part of the microbial food web in Lake Michigan were examined using a three-dimensional (3-D) coupled biological and physical model. The model was driven by the realistic meteorological forcing observed in March 1999. Wind-induced surface wave dynamics were incorporated into the physical model to generate the bottom flux. The model-generated benthic detrital fiux was assumed to be proportional to the difference between model-calculated and critical stresses at the bottom. The model results indicate that detrital flux at the bottom was a key factor causing a significant increase of phosphorus and detritus concentrations in the nearshore region of the springtime plume. Inside the plume the sediment-resuspended bottom detritus flux could directly enhance heterotrophic production, while outside the plume, detrital flux from river discharge might have a direct contribution to the high abundance of bacteria and microzooplankton in the nearshore region. Mo&l-data comparison on cross-shore transects near Chicago, Gary, St. Joseph, and Racine suggests that other physical and biological processes may play a comparative role as the bottom detritus flux in terms of the spatial distribution of bacteria and microzoplankton. A more complete microbial food web model needs to be developed to simulate the hetereotrophic process in southern Lake Michigan.