NITRATE REDUCTASE ACTIVITY 397 



tration by centrifugation, cells were counted by the Sedgewick— 

 Rafter strip-count method (Jackson and Williams, 1962). Usually 

 about 500 cells/ml were counted. 



Wutrient Concentration in Seawater 



Subsamples (100 ml) from the pooled 12 liters of water collected 

 at each station were frozen for later nutrient analysis. The nitrite 

 concentration of the water was determined by the diazotization— 

 couphng reaction; the nitrate was reduced to nitrite and determined 

 by passage through a copperized cadmium column (Strickland and 

 Parsons, 1968); and ammonium was determined by the alkaline 

 hypochlorite method of Solorzano (1969). 



RESULTS 



Phytoplankton Population 



Phytoplankton cell concentrations did not vary greatly from 

 intake to cut over the 1-year sampling period. Two blooms occurred, 

 one in the spring, peaking at about 2 x 10^ cells/liter, and one in 

 midsummer, peaking at about 3.8 x 10^ cells/liter (Fig. 2). 



Of the fifteen different genera identified, the majority are 

 diatoms, Skeletonema costatum, Thalassiosim nordenskioldii, Asteri- 

 onella japonica, Chaetoceros sp., Thalassionema nitzschoides, and 

 Rhizosolenia fragillissima. Other dominants include the flagellates 

 Rhodomonas minuta and Rhodomonas amphioxeia and the dino- 

 flagellates Dinophysis sp., Peridinium sp., and Prorocentrum sp. 

 These genera were entrained through the plant from January 1973 to 

 January 1974. The same species were found to be abundant in Long 

 Island Sound by Conover (1956), in Block Island Sound by Riley 

 (1952), and in the Niantic Bay estuary by Marshall and Wheeler 

 (1965). 



Chlorination, Primary Productivity, and Nitrate Reductase Activity 



When there was no chlorine application during a study period, 

 primary productivity was unaffected by entrainment (Table 1). 

 Chlorination at every concentration used in this study reduced 

 primary productivity. Continuous chlorine application at the highest 

 dosage (1.2 ppm) reduced productivity by 89% at the discharge and 

 84% at the cut, as compared with intake water productivity. Free 

 residual chlorine concentrations at the discharge ranged from 0.4 

 ppm at the highest chlorine application (1.2 ppm) to below 

 measurable amounts at addition rates of 0.4 ppm and less. No 



