limiting phytoplankton production in the shallow estuarine system near 

 Beaufort, North Carolina, were identified. Nitrogen was the primary 

 limiting nutrient and was found to be phosphorus limiting at times. Samples 

 receiving a complete enrichment medium plus organic substrates poor or 

 lacking in nitrogen and phosphorus showed no significant increase in 

 relative photosynthesis over unenriched controls, even though there was 

 a significant decrease in the nitrogen and phosphorus concentrations in 

 the enriched samples. This suggested that microbial immobilization 

 of nitrogen and phosphorus during decomposition of organic matter may 

 limit nutrient availability to phytoplankton and in part account for the 

 general paucity of inorganic nutrients present in this shallow system. 

 The estimated amounts of carbon, nitrogen and phosphorus entering the 

 estuarine system in the form of partially decayed Spartina alterni flora 

 each year are given. Data suggested that an annual cycle in nutrient 

 concentration in the estuarine system in part may result from shifts in 

 the equilibrium between microbial immobilization and remineralization. (A. A.) 



Keywords: phytoplankton, estuaries, nutrients. North Carolina 



II-E-7 



Williams, R.B. 1973. Nutrient levels and phytoplankton productivity in 

 the estuary. Pages 59-89 jn^ R.H. Chabreck, ed., Proceedings of the 

 coastal marsh and estuary management symposium. Louisiana State 

 University, Baton Rouge. 



Phytoplankton are ubiquitous photosynthetic plants with a potential 

 for a large production from a small standing crop due to rapid cell 

 division and an absence of non-photosynthetic tissue. Maximum daily 

 rates reported for estuarine phytoplankton production are 22.6 (gross) 

 and 16.4 (net) g C/m^, Annual rates range from 100 to over 546 g C/m^ 

 for gross production, and from -11 to 220 g C/m^ for net production. 

 In shallow estuaries, rates of production tend to follow the seasonal 

 cycle in water temperature. Maximum rates of production per unit 

 volume usually occur near the heads of estuaries and maximum rates of 

 production per unit area near the mouths. In estuaries along the 

 southeastern U.S. coast, rooted plants may often outproduce the phytoplankton. 

 Nutrient enrichment studies indicate the available nitrogen commonly 

 limits estuarine and coastal phytoplankton production; there is normally 

 ample phosphorus relative to nitrogen. Physiological studies reveal, 

 however, that many species of phytoplankton can thrive at the inorganic 

 nitrogen concentrations commonly present in estuaries. It is likely 

 that the actively photosynthesizing species are adapted to existing 

 nutrient conditions. Nutrient enrichment causes a shift to species 

 adapted to higher nutrient levels as well as an increase in phytoplankton 

 biomass and production. (A. A.) 



Keywords: nutrient levels, phytoplankton, productivity, estuaries, 

 U.S. general 



84 



