406 



PECK AND WARREN 



X 



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JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC. 



1973 



JAN. 

 1974 



Fig. 5 Ammonium concentrations at power-plant intake and at the 

 cut on various sampling dates from January 1973 to January 1974. 



Our results indicate that photosynthesis is more sensitive to 

 chlorination than is nitrate reductase activity. Either a real difference 

 between photosynthesis and nitrogen assimilation occurs, or nitrate 

 reductase activity measures an effect on the level of an enzyme, 

 whereas productivity measures an activity. Recovery of the nitrate 

 reductase enzyme at the cut after depression at the discharge by the 

 two highest chlorine dosages is consistent with a fairly rapid turnover 

 rate for the enzyme and may indicate that chlorine does not have 

 any long-term effects on the ability of phytoplankton to synthesize 

 nitrate reductase. Further recovery of nitrate reductase activity may 

 taJ^e place after exposure to ocean water with no added chlorine. 



It appears that nitrate reductase activity is stimulated in transit 

 through the pond during 6 to 9 hr of exposure to temperatures 

 increasing to ~18°C, such as occurred in March and April. At some 

 temperature between 18°C, occurring at the cut in the spring, and 

 27° C, occurring at the cut in the fall, there is a shift from stimulation 

 to inhibition of nitrate reductase. For example, on Mar. 30, when the 

 temperature at the cut was 17.4° C, nitrate reductase activity at the 

 cut increased 25.9% above intake activity, but on Aug. 2, when the 

 temperature was 31. 3° C, activity decreased 88%. Nitrate reductase 

 activity never decreased after a 2-min exposure to temperature 

 increases during passage through the plant but was affected after 

 transit through the pond and exposure for 6 to 9 hr to a change in 



