Model Studies on the Interactions Among Carbon Substrates, Bacteria and Consumers in a Salt Marsh Estuary

We have developed a lagrangian computer simulation model to investigate the interactions between dissolved and particulate carbon-substrates of detrital (vascular plants) and phytoplankton origin, microbes attached and free-living in the water column, and consumers of these substrates for a specific estuarine water body: the Duplin River, Sapelo Island, Georgia. Model simulation experiments were directed toward investigating the potential for both carbon resource and heterotrophic grazing as controls on free-living and particle-attached bacterial densities. Given available information from the literature and our own work, we present simulations of the model that approximate what one generally finds in this estuary during summer relative to the dynamics of particulate organic carbon (POC), dissolved organic carbon (DOC), free-living bacteria and microconsumers. Predicted dynamics of the bacteria were insensitive to macroconsumer grazing but highly sensitive to the parameter values governing microconsumer grazing rates and metabolism. Within reasonable constraints of the parameter values used, however, we were unable to reduce the predicted densities of particle-attached bacteria by manipulation of either resource (carbon) availability or grazing pressures. We propose several alternate hypotheses that might explain this discrepancy between model results and what is generally reported for natural systems.