Much of the uncertainty about the effects of nutrient loading on phytoplankton composition stems from our inadequate understanding of how nuisance bloom-formers such as cyanobacteria succeed in dominating plankton assemblages. In enriched lakes, cyanobacteria appear to migrate from bottom and deepwater habitats to occupy the upper layers of the open water, and as nutrient conditions permit, cyanobacteria extend their use of the photic zone until, by growth and migration, they monopolize lights in the heterogeneous environments of stratified lakes as effectively as they do in the homogeneous environments of shallow, mixed lakes. This research is a coordinated lake (mesocosm and whole- lake) and laboratory (cyclostat) set of experiments to obtain a better understanding of the ecological significance of surface blooms and their consequences at consumer as well as producer levels. Our objectives are (1) to determine the significance of the oxidation state nitrogen and (2) the relative availability of carbon nitrogen and phosphorus to cyanobacterial buoyancy regulation and bloom formation, (3) to evaluate the effects of C- N-P interactions on dominance of the photic zone and the phytoplankton by cyanobacteria and (4) to evaluate the effects of different degrees of cyanobacterial success on trophic-level interactions. The project will contribute to basic limnology, while providing valuable information which will add to the knowledge base used in lake management.
