Phytoplankton assemblages and their periodicity in stratifying lake systems

A subjective analysis of the seasonal periodicity of phytoplankton populations in several natural lakes and experimental lake systems (Lund Tubes) has shown that the direction and patterns of change are both general and predictable. The paper distinguishes between autogenic successional changes, consistent with increasing community complexity and segregation, and allogenic changes resulting from turbulent disruption of the stratified system. The periodicity of the assemblages recognized is resolved through the interaction of two major variables – nutrient availability and column stability. A simple possibility matrix is proposed which can account for the observed changes in community structure. The principal pathways in eutrophic lakes (diatoms → Volcocales → Nostocales → dinoflagellates or Microcystis , with reversions through 'summer diatom'assemblages) and in mesotrophic lakes (diatoms → Chrysophyte/Sphaerocystis → dinoflagellates, with reversions through 'summer diatom-desmid'assemblages) are generally consistent with the growth and survival strategies of the principal algal species concerned.