Some physiological‐biochemical characteristics of planktonic blue‐green algae during bloom formation in three Salopian meres

SUMMARY. Levels of cellular orthophosphate concentration, alkaline phosphatase activity, photosynthesis and nitrogenase activity of natural populations of blue‐green algae collected during the summer of 1976 from the surface waters of three eutrophic lakes were determined under controlled conditions. Intracellular concentrations of surplus stored phosphorus remained high and alkaline phosphatase activity remained low during the formation and decline of the surface bloom, which indicated that available phosphorus does not become limiting to growth. In contrast, declining rates of nitrogenase activity and net photosynthesis were recorded, particularly in those blooms of shorter duration. An increase in numbers of bacteria during the summer may account for the observed fall of net photosynthetic rates, since gross rates did not change as markedly. There was appreciable nitrogenase activity proceeding and during the differentiation of akinetes, and the cellular C/N atomic ratio of sporulating populations was lower than in non‐sporulating algae. It is suggested that the onset of sporulation in surface blooms is initiated by an imbalance of the normal vegetative growth of the algal cells and of their carbon and nitrogen metabolism.