ARE PHYTOPLANKTON DYNAMICS IN RIVERS SO DIFFERENT FROM THOSE IN SHALLOW LAKES

This paper introduces a series of contributions to the ninth meeting o f the International Association of Phytoplankton Taxonomy and Ecology, held in Belgium during July, 1993. It draws from the original papers a synthesis which supports the view that the successful species in riv ers and turbid shallow lakes are selected primarily on their ability t o survive high-frequency irradiance fluctuations as they are circulate d through steep light gradients. The selective distinction is less tha n that which discriminates between plankton of deep lakes and shallow lakes or even between clear and turbid shallow ones. River plankton is , however, dependent on fast growth rates but its survival in rivers i s aided by a suite of water-retentive mechanisms. The ecology of turbi d systems is dominated by physical interactions, those biotic interact ions traditionally believed to regulate limnetic communities being sup pressed and rarely well-expressed.