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SUPERSATURATION OF NITROGEN IN THE COLUMBIA RIVER AND ITS 

 EFFECT ON SALMON AND STEELHEAD TROUT 



BY WESLEY J. EBEL, FISHERY BIOLOGIST 

 BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY 

 SEATTLE, WASHINGTON 98102 



ABSTRACT 



The nitrogen gas regime in the Columbia River was 

 studied in 1966 (from Grand Coulee Dam, Wash., to the 

 estuary at Astoria, Oreg.) and in 1967 (from Priest 

 Rapids Dam, Wash., to the estuary). Dissolved nitrogen 

 was subject to considerable seasonal fluctuation and 

 varied with flow of water over spillways of dams; it was 

 normal (near 100-percent saturation) in the fall and 

 winter when no water was spilled, and high (above 135- 

 percent saturation) in the spring and summer when 

 large volumes of water were spilled. Some saturation 



levels over large areas were high enough and lasted long 

 enough to be potentially dangerous to salmon 

 (Oncorhynchus spp.) and steelhead trout {Salmo 

 gairdneri). 



Supersaturation of nitrogen at Priest Rapids Dam 

 lowered the tolerance pf juvenile fish to temperature 

 increases, and some showed symptoms of gas bubble 

 disease. Field studies to determine the effects of high 

 levels of dissolved nitrogen on adult salmon and steel- 

 head trout did not provide conclusive results. 



Observations in tlie spring of 1965 by tlie Wash- 

 ingt.on State Department of Fisheries and the 

 Bureau of Commercial Fisheries showed that 

 saturation of dissolved nitrogen at some sites in 

 the Columbia River was as high as 125 percent. 

 Because levels of this magnitude had protluced gas 

 bubble disease in adult and juvenile salmon 

 (Rucker and Hodgeboom, 1953; Harvey and 

 Cooper, 1962; and Westgard, 1964), additional 

 surveys were made in 1966-67 to attempt to deter- 

 mine whether high levels of dissolved nitrogen 

 might be responsible for losses of adult salmon 

 and poor production of young fish at spawning 

 channels. 



The first phase in tlie study of nitrogen and 

 oxygen concentrations (February-November 

 1966) was primarily to determine the cause of 

 supersaturation of dissolved nitrogen and to deter- 

 mine seasonal variations. Water samples were 

 taken from 26 sites between Grand Coulee Dam, 

 Wash., near the Canadian border, and Astoria, 

 Oreg., at the mouth of tlie river. The second phase 

 (March-October 1967) was to determine the effect 

 of nitrogen sujiersaturation on adult and juvenile 

 salmon. We suspected that gas bubble disease was 

 one of the factoi-s in losses of adult and juvenile 



Published June 1969. 



chinook salmon {O. taJiawytscha) migrating be- 

 tween dams. The studies in 1967 concentrated on 

 obtaining field evidence of such losses. 



This report discusses the amounts of dissolved 

 nitrogen in 1966-67, the effect of dams and reser- 

 voirs on saturation, the seasonal variation and 

 duration of supersaturation, and the effect of 

 supersaturation of nitrogen on juvenile and adult 

 salmon and steelhead trout {Salmo gairdTieri) in 

 the Columbia River. 



METHODS 



Descriptions of the sampling stations, analyti- 

 cal tecliniques, and other experimental procedures 

 are given in this section. 



SAMPLING STATIONS AND TECHNIQUE 



Twenty-six principal sampling stations were 

 established along the Columbia River between the 

 forebay of Grand Coulee Dam and the estuary at 

 Astoria (fig. 1). All stations except 13, 25, and 26 

 were either in midreservoir, about 500 m. upstream 

 from the dam, or on the spillway side of the river, 

 about 500 m. below. Samples of water were taken 

 at the surface and at 10-m. depths at the forebay 

 stations. The spillways discharge from the surface 

 down to a maximum depth of about IO14 m., and 



FISHERY BULLETIN: VOL. 68, NO. 1 



