Physiological Changes During the Course of Blooms of Aphanizomenon flos-aquae

Several aspects of the cellular composition and metabolism of Aphanizomenon flos-aquae (L.) Ralfs were measured during the course of four blooms in small prairie lakes. Much larger changes were observed in these than in the nutrient concentrations of the water, suggesting the former to be more sensitive indicators of the progress of the bloom. These changes were reminiscent of the changes in batch cultures growing into nutrient deficiency. All four blooms developed characteristics of P deficiency, and to a lesser extent of N deficiency. In spite of their similar characteristics, three blooms collapsed dramatically, while the fourth did not. While P deficiency seems to play an important part in setting conditions for a collapse, it is not the factor that triggers the collapse.