The role of zooplankton in the nitrogen dynamics of a shallow estuary

Abstract

The rates of ammonia and urea release by selected species of copepods collected from the estuary at Beaufort, North Carolina, during September through April in 1973 and 1974 varied with species, sex, season, and feeding state. The rate of ammonia assimilation by phytoplankton was greatest in September and April, and there were no significant differences associated with tidal changes. Rates of ammonia assimilation by phytoplankton ranged from 1 to 101 mg N m −3 day −1 while ammonia release by Zooplankton ranged from 0.1 to 9.7 mg N m −3 day −1. The productivity of the phytoplankton in the estuary must depend largely upon regenerated nitrogen since the maximum rate of assimilation of ammonia by phytoplankton was often the same as total-nitrogen uptake estimated from primary productivity. The average rate of ammonia release by zooplankton was 8% of the average, ammonia assimilation by phytoplankton. I conclude that, while all sources of regenerated nitrogen are used and therefore of value in a system depending almost totally upon regeneration, Zooplankton are not the major source of regenerated nitrogen in this estuary.