Effect of Dissolved Nitrogen on Fish 



Wild and hatchery stocks of juvenile fall 

 Chinook salmon and wild spring chinook salmon 

 were held in cages at various depths in the 

 forebay of Ice Harbor Dam and were inspected 

 for numbers of dead fish and symptoms of gas 

 bubble disease. Fifty fish were placed in each 

 cage and observed for 7 days. In each of these 

 tests the deep cage, or the enclosure with fish 

 held at 3 to 4 m, was designated as the control 

 cage because at these depths concentrations of 

 dissolved nitrogen up to about 135 9r of satur- 

 ation would be compensated for by the hydro- 

 static pressure. Concentrations of dissolved 

 nitrogen and water temperatures were recorded 

 at the beginning and end of each test. Numbers 

 of survivors with and without gas bubble di- 

 sease symptoms were also recorded at the 

 termination of each test. 



Samples of juvenile chinook salmon and steel- 

 head trout were taken from the gatewell bypass 

 trap at Ice Harbor Dam throughout the migra- 

 tion period and were examined for external 

 symptoms of gas bubble disease. One hundred 

 or more fish were captured for study during 

 each sampling. 



Adult chinook salmon were examined at 

 Rapid River Hatchery, Riggins, Idaho, for ex- 

 ternal symptoms of gas bubble disease. The 

 fish were captured in a trap near the hatchery 

 and were examined before they were moved to 

 the holding pond. 



During each aircraft flight for data on dis- 

 solved nitrogen concentrations, I also searched 

 along the rivers for dead specimens of adult 

 salmon and trout. Numbers of dead fish and 

 location and date of the sightings were recorded 

 and then related to the concentrations of dis- 

 solved nitrogen gas near the dead fish. 



RESULTS 

 Dissolved Nitrogen Concentrations 



Concentrations of dissolved nitrogen gas (as 

 well as concentrations of dissolved oxygen and 

 related water temperatures) at sampling sites 

 in the Columbia and Snake Rivers are listed 

 in Table 2. Concentrations in the Columbia 



were lower in 1970 than in the previous years 

 1968-69 (Beiningen and Ebel, 1971), except 

 during the peak flow period in the first week of 

 June. For example, concentrations between 

 McNary and Bonneville in early May ranged 

 between 100 and 133% of saturation in 1968, 

 128 and 144% in 1969, and 96 and 107% in 

 1970. The Snake River, however, had some 

 extremely high concentrations. 



The Snake River was supersaturated with 

 dissolved nitrogen (129% below Little Goose 

 Dam) on the first survey, 7 April. During the 

 next 2 months, concentrations between Little 

 Goose and Ice Harbor Dams increased, reach- 

 ing a high on 3 June of 146% of saturation in 

 the forebay of Lower Monumental Dam. The 

 concentrations remained high in the river until 

 21 July when marked reduction was noted. This 

 reduction was no doubt caused by the reduced 

 spill at Little Goose Dam — from about 1,981 

 cubic meter ^second (cms) (70,000 cfs) on 7 

 July to 368 cms (13,000 cfs) on 21 July. On 

 18 August (the last survey), levels had re- 

 turned to normal — near 100%. A comparison 

 of average percentage saturation of dissolved 

 nitrogen gas in the forebay of Lower Monu- 

 mental Dam with mean daily spill at Little 

 Goose Dam (Figure 2) shows a sharp increase 

 in concentration of dissolved nitrogen from 5 

 May to 19 May at Lower Monumental as spill 

 volume increased at Little Goose. 



Nitrogen-Lower Monumenlol Dam 



90 -ii;; 



6-23 7-7 



Figure 2. — Average concentration of dissolved nitrogen 

 gas in forebay of Lower Monumental Dam and mean 

 daily spill of water at Little Goose Dam, 7 April to 

 7 July 1970. (To convert from cubic feet to cubic 

 meters, multiply cubic feet by 0.0283.) 



