Dissolved Gas i DE w eitkamp 



Supersaturation: 



Live Cage Bioassays at 



Rock Island Dam, Washington 



ABSTRACT 



Three live cage bioassays using juvenile chinook salmon 

 (O. tshawytscha) were conducted in supersaturated Columbia 

 River water at the Rock Island Dam forebay. The tests of 10 and 

 20 days' duration utilized volition, specific depth, and inter- 

 mittent exposure cages which were suspended between the sur- 

 face and a depth of 4 m. The volition cages extended from the 

 surface to depths of 2, 3, and 4 m. The four specific depth cages 

 were 1 m deep cages suspended at 1 m intervals between the 

 surface and a depth of 4 m. Intermittent exposures were achieved 

 by raising and lowering three 1 m deep cages in the water 

 column daily to change the actual level of supersaturation 

 experienced by the test fish. 



At total dissolved gas supersaturations of about 120% in the 

 reservoir water, significant mortalities were encountered only 

 in fish held within 1 m of the surface. Fish held within 2 m of 

 the water's surface for a period of 16 hr per day suffered 

 significant mortalities only when the supersaturation rose to 

 about 125% and above. The effects of supersaturations above 

 about 125% appear to be much greater than supersaturations 

 below this level. Fish allowed to seek the depth of their choice 

 in the 4 m deep volition cage did not suffer mortalities at satura- 

 tions of 119% and 128%, although some developed gas bubble 

 disease lesions. Most fish showing slight to severe gas bubble 

 disease lesions were able to recover when placed at a depth of 

 3 to 4 m in the supersaturated water. 



One of the obvious means of determining the effect 

 of a given water quality parameter on fish is the 

 bioassay experiment. This technique has been 

 applied to the investigation of the effects of dis- 

 solved gas supersaturation on fish. Bioassays in gas 

 supersaturated water have been conducted by 

 many workers under both artificial laboratory and 

 natural field conditions. Most of the experimental 

 work dealing with the effects of dissolved gas 

 supersaturation has been conducted in the labora- 

 tory using artificially supersaturated water or, in 

 some cases, supersaturated Columbia River water 

 in shallow tanks. Several live cage bioassays study- 

 ing the effects of depth in relation to supersatura- 

 tion have been conducted in the Columbia and 

 Snake Rivers by Ebel (1969 and 1970) and Meekin 

 and Turner (1974). 



The live cage bioassays conducted by Ebel at 

 Priest Rapids and Ice Harbor Dams tested varying 

 high levels of supersaturation. The nitrogen levels 

 during the three Priest Rapids tests in 1967 ranged 

 from a high of 143% at the start of the first test to 

 118% at the end of the third test. The 1970 Ice 

 Harbor tests exposed juvenile chinook for 7 days to 

 nitrogen levels of 127% to 134%. At some time dur- 

 ing most of these tests, supersaturations of 130% or 

 greater were experienced. It is therefore difficult 

 to determine if the mortalities resulted from the 

 highest levels encountered or from continuous 

 levels above 120% or 125%. 



The following study was therefore designed to 

 test juvenile chinook under similar field conditions 

 at lower, but more consistent levels of supersatura- 

 tion. The snowpack of the 1973-74 winter was 

 sufficient to ensure at least moderate levels of 

 supersaturation in the mid region of the Columbia 

 River during the 1974 runoff period. The study was 

 conducted at Rock Island Dam on the mid Columbia. 

 Favorable weather and water conditions allowed 

 the levels of supersaturation to remain quite con- 

 stant at the test location during test periods. 



The study was also designed to test the effect of 

 intermittent daily exposures to gas supersaturation. 

 It is believed that under natural conditions juve- 

 nile salmonids and other fish are most likely ex- 

 posed to high gas levels on an intermittent basis. 

 In some areas this is due, in part, to the inter- 

 mittent production of supersaturation conditions, 

 as the spill may occur intermittently at dams on 

 smaller rivers. In certain areas, such as the mid and 

 lower Columbia River, however, supersaturation 

 can be present continuously for several months at a 

 time. Fish are intermittently exposed to this con- 

 tinous supersaturation by their vertical move- 

 ments in the water column. The live cage bioassay 



Weitkamp: Parametrix, Inc., Environmental Services Section, 

 Seattle, Washington. 



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