Sequestration of nitrogen and phosphorus by planktonic algae and bacteria in limnetic and marine waters

Bacteria have been shown to contribute significantly to the plankton biomass measured as carbon. This is particularly the case in limnetic systems, and for both types of systems in oligotrophic waters. Bacte ria have nitrogen and particularly phosphorus requirements that are c onsiderably higher than those of algae. One would therefore expect th at they may bind up an even higher share of nitrogen and particularly of phosphorus than they do of carbon. As both nitrogen and phosphoru s are known to limit the growth rate of algae in pelagic waters, the sequestration of macronutrients by bacteria will in a dynamic way aff ect carrying capacity and biomass development of algae. Based on dat a available in the literature on biomass, N and P requirements of alg ae and bacteria, and information on N and P status of these two group s in limnetic and marine waters, their sequestration of N and P will be calculated. Predictions will be evaluated based on data sets from limnetic and marine waters were elemental content of organisms has be en determined. Algae and bacteria have variable N and P content depe nding on limiting nutrient and specific growth rate, and also bacteri a seem to obey the Droop model for nutrient limited growth. Both mini mum and maximum cell quota for P is typically 10X higher for bacteria than for algae. For N, minimum and maximum cell quota of bacteria ar e 3X and 2X higher than those of algae. Whereas P seems to be the pri mary limiting nutrient for both algae and bacteria in limnetic system s, marine waters are generally more balanced compared to the requirem ents of the organisms. Calculated sequestration of N and P for both limnetic and marine waters covering a wide range in trophic state wil l be shown, and its implications on N and P cycling will be discussed .