NITRATE REDUCTASE ACTIVITY 401 



as compared with intake levels. A 1.0-ppm chlorine application 

 reduced nitrate reductase activity 26% at the discharge and 15% at 

 the cut. 



Temperature, Ammonium, Primary Productivity, 

 and Nitrate Reductase Activity 



Generally, temperature increases above 9°C resulting from 

 power-station generation depressed productivity at the discharge and 

 cut relative to that at the intake (Table 2). Percent nitrate reductase 

 activity per cell per hour at the cut was stimulated after 6 to 9 hr of 

 exposure to temperatures increasing to 17° C through the pond and 

 to the cut, but, when temperatures exceeded 25° C, activity was 

 greatly depressed. The power plant was not chlorinating on any of 

 these sampling dates. Ambient nitrate, nitrite, and ammonium 

 concentrations remained essentially the same after passage through 

 the power plant. 



Figure 3 compares nitrate reductase activity at the plant intake 

 with that at the cut for random sampling dates from January 1973 to 

 January 1974. Figures 4 and 5 show changes in temperature and 

 ammonium concentrations during this time. During March and April 

 activity at the cut was stimulated above ambient nitrate reductase 

 activity at the intake. Intake temperatures ranged from 4.3 to 9.9°C 

 during this time, and cut temperatures were 11.5 to 18.1°C. From 

 August through January 1974, nitrate reductase activity at the cut 

 dropped sharply below that at the intake. Intake temperatures during 

 this interval ranged from 22 to 6.4° C, and cut temperatures ranged 

 from 34 to 17.9°C. From September through January 1974, 

 ammonium concentrations at the cut were highest, ranging from 8 to 

 14 /ig atoms/liter. Therefore, the depression of nitrate reductase 

 activity at the cut in August 1973 appears to be caused by 

 temperature increases resulting from station generation, and that 

 from September through January 1974 is caused by increases in 

 ammonium concentration. 



On seven dates in August 1973, the recovery of nitrate reductase 

 activity after heating was tested by use of 10 liters of seawater, 

 sampled from a depth of 1 m at each station (intake, discharge, and 

 cut), at the ambient intake temperature. The water was held in 

 dialysis tubing for periods of 1, 4, and 24 hr, and a nitrate reductase 

 assay was run after each incubation period. The nitrate reductase 

 activity of these samples, depressed at the cut after transit through 

 the quarry at a temperature range of 30 to 34°C, did not recover to 

 intake levels after 24 hr of incubation at ambient intake temperature. 



