Response of Anabaena to pH, Carbon, and Phosphorus

The objectives were to study the roles of carbon and phosphorus in cultural eutrophication, and to investigate the observation that blue-green algal blooms are frequently associated with a pH greater than 8.4. These objectives were met by the manometric determination of rates of photosynthesis and respiration in the blue-green alga, Anabaena flos-aquae as functions of pH, total inorganic carbon, and orthophosphate. The photosynthetic rate was independent of carbon concentrations from 30 ppm Na₂CO₃–300 ppm Na₂CO₃. At pH values of 8.3 or less, photosynthetic rate is dependent upon pH and independent of P concentration. At higher pH values, the reverse is true. Respiration was independent of pH, carbon, and phosphorus. The association of blue-greens with alkaline pH values is related to a H⁺ effect and is independent of the ionic forms of carbon and phosphorus.