1. Biological 



A. Intermittent exposure to supersatu- 

 rated and equilibrated N 2 levels 



B. Detection and avoidance of N 2 super- 

 saturated water 



C. Bioassay of prevailing Columbia River 

 conditions 



1. deep versus shallow tanks 



2. artificially created N 2 levels 



D. Description of the vertical distribu- 

 tion of fish using depth sounding 

 gear 



2. Physical Monitoring 



A. Daily gas saturation levels at Prescott 



B. Gas equilibration characteristics in 

 the Columbia River between The 

 Dalles Dam and Prescott, Oregon 



INTERMITTENT EXPOSURE 



The intermittent exposure tests were planned 

 to assess the effect of intermittently exposing fish 

 to either 130, 120, 110 or 100% N 2 saturation. Infor- 

 mation from these tests would help determine if 

 manipulation of water flows (spill) at dams could 

 possibly afford the fish some relief from gas super- 

 saturated water conditions during critical N 2 

 periods. 



Groups of at least 10 fish were held in separate 

 175 B tanks in which the N 2 levels 130, 120, 110, 

 and 100% saturated were alternately switched as 

 per the following diagram: 



Percent N 2 

 130 120 110 



I t I 



100 100 100 



The time cycle, in two test tanks, was based on 24 hr, 

 e.g. one tank, 8 hr at 130% and 16 hr at 100% and the 



other, 16 hr at 130% and 8 hr at 100% N 2 ; the same 

 pattern was used for the 120 and 110% N 2 tests. 

 The switching was done by valving, which elimi- 

 nated handling the fish. Test temperatures were 

 between 10 and 13°C. The alternating cycle was 

 continued for 192 hr (8 days). For this report the 

 results of the 130% to 100% N 2 tests are used to 

 present the general results. Table 1 summarizes the 

 results of intermittent exposure to 130 and 100% N 2 . 

 Compiled in Table 1 is the time (hr) to 50 and 100% 

 mortality when the fish were exposed to 130% N 2 

 for 24, 16, and 8 hr. 



With the exception of steelhead and white- 

 fish the 16- or 8-hr exposure enhanced survival 

 time to 50% mortality over that recorded for a 

 constant (24-hr) exposure to 130% N 2 . At the 100% 

 mortality level the 16- or 8-hr exposure enhanced 

 survival of all species over that recorded for fish 

 held constantly at 130% N 2 (Table 1). 



DETECTION AND AVOIDANCE OF N 2 

 SUPERSATURATION 



Juvenile salmonids are being tested at the 

 Prescott Facility to determine if they can detect 

 and/or avoid N 2 supersaturation. Homogenous 

 groups of fish are introduced into the end of a test 

 tank (Fig. 2) which provides a lateral choice of two 

 channels, one containing dissoived nitrogen at 

 130% saturation and the other at 102% saturation. 

 Water depth in the channels is maintained at 0.33 m 

 to eliminate the effects of hydrostatic pressure. 

 External influences are minimized by placing cur- 

 tains around the test tanks and by limiting inspec- 

 tion and water sampling to twice daily. Test dura- 

 tion is 192 hr or until 50% mortality occurs. A 



TABLE 1 Time in hr to 50 and 100% Mortality for Fish Subjected 



to 130% N 2 Saturation for Either 24, 16, or 8 hr of Each 24-hr Cycle 



During 192-hr Intermittent Exposure Test. The fish were 



alternately exposed to 130 and 100% N 2 . 



12 Blahm, McConnell, Snyder 



