Quantifying external and internal nitrogen and phosphorus pools, as well as nitrogen and phosphorus supplied through remineralization, in coastal marine plankton by means of a dilution technique

A theoretical framework was developed for analysing dilution assays under conditions where phytoplankton growth might also be nutrient-limited. The theory, which acounts for growth on available internal and external pools as well as on nutrients supplied through remineralization by grazers was applied to experiments performed in nutrient-impoverished waters in the Oslofjord, Norway, in summer 1988. The phytoplankton had intracellular stores of P sufficient for several hours of growth in all experiments, while internal stores of N were undetectable in four out of six cases. Dissolved N pools appeared to be of greater importance to the algae as a nutrient reservoir than were dissolved P pools. Significant nutrient supplies from remineralization were identified on three out of six occasions, compensating for around half of the estimated grazing losses in each case. The supplies of remineralized N and P were closely balanced with respect to the growth demands of the phytoplankton, indicating that the surplus of cellular P originated from other sources. -from Authors