Plant community dynamics in a chain of lakes: principal factors in the decline of rooted macrophytes with eutrophication

Species frequency, biomass distributions, nutrient concentrations and responses to experimental nutrient enrichment and shading were compared at Shoe lake and East Graham lake (Mich.), to elucidate principal factors controlling macrophyte dynamics, to explain why rooted macrophyte (RM) growth declined with eutrophication and to test existing models. Shoe lake was more eutrophic and exhibited low diversity and productivity of RM, primarily because of shading. East Graham lake was less eutrophic. Low availability of nitrogen restricted growth of shading plants and resulted in clearer water, higher productivity and greater diversity of RM. In East Graham lake, phytoplankton were not suppressed allelopathically by macrophytes. A direct relationship was evident between nutrient loading, increased growth of phytoplankton, periphyton and non-rooted macrophytes, and the decline in RM. A general descriptive model of aquatic plant relationships to eutrophication is presented. There are 52 references.