NITRATE REDUCTASE ACTIVITY 393 



The effects of various levels of temperature and chlorine in the 

 cooling water entrained through the Millstone Nuclear Power Plant 

 on nitrate reductase activity and primary productivity of the natural 

 phytoplankton population were tested. 



Nitrate reductase catalyzes the reduction of nitrate to nitrite: 



NO7 + 2H^ + 2e~ ^ NO7 + H2O 



The initial reduction of nitrate is the rate-limiting step in the 

 assimilation of nitrate (Beevers and Hageman, 1969). The nitrite 

 produced is further reduced to ammonia by nitrite reductase and is 

 assimilated by glutamic dehydrogenase to produce glutamic acid, the 

 nitrogen source for other amino acids. 



Nitrate reductase is light and heat labile and is relatively unstable 

 in vivo and in vitro (Beevers and Hageman, 1969; Schrader et al., 

 1968). Eppley, Packard, and Maclsaac (1970) and Packard et al. 

 (1971) reported an optimum temperature of around 15°C for the 

 nitrate reductase activity of a natural population of marine phyto- 

 plankton in the Peru current. There is evidence that a large and 

 sudden rise in temperature lowers nitrate reductase activity of 

 Hordeum vulgare L. (barley) (Travis, Jordan, and Huffaker, 1969). 



Electric-power generating plants usually entrain large volumes of 

 water for cooling purposes and discharge heated effluents that 

 exceed maximum ambient temperatures. The nitrate reductase 

 activity of entrained phytoplankton may be affected by thermal or 

 chlorination stresses during passage through power-plant condensers. 



Briand (1975) attributed large reductions in phytoplankton 

 bio mass to the magnitude of increases above ambient temperature at 

 two southern California coastal power plants. Carpenter, Peck, and 

 Anderson (1972), reported substantial phytoplankton productivity 

 losses at the Millstone plant at all levels of continuous and 

 intermittent chlorination, but the effects of temperature shock on 

 nitrate reductase activity and productivity were not studied. If the 

 level of phytoplanktonic nitrate reductase is influenced by photo- 

 synthetic rate, then chlorination could mask any temperature effects 

 on this enzyme. To determine the effects of temperature increase 

 resulting from power-station generation, we measured nitrate reduc- 

 tase activity and primary productivity over an annual cycle of 

 temperature fluctuations from January 1973 through January 1974. 

 Coordinating sampling wdth plant operations allowed us to monitor 

 nitrate reductase and primary productivity over a range of tempera- 

 tures and at chlorination levels of 0.0 to 1.2 ppm [the highest dosage 

 studied by Carpenter, Peck, and Anderson (1972)] . 



