Effect of John Day Dam on Dissolved Nitrogen Concentrations and Salmon in the Columbia River, 1968

Abstract

Concentrations of dissolved nitrogen gas were measured in the lower 640 km of the Columbia River from April to September 1968 to determine the effect of newly-constructed John Day Dam on nitrogen saturation downstream. Observations were also made of symptoms of gas bubble disease and mortality in juvenile and adult salmon. Heavy spillway discharge at the dam caused abnormally high (123–143%) supersaturation downstream, and mortalities of juvenile and adult salmon (Oncorhynchus spp.) and steelhead trout (Salmo gairdneri) were substantial. Delays in passage at John Day and The Dalles Dams coupled with supersaturation of nitrogen gas caused the mortalities. The authors recommended that in future dam construction one or more turbines should be operable before the reservoir is filled. Increasing the flow through the turbines while decreasing flow over the spillways will reduce concentrations of nitrogen. In addition, every possible effort should be made to reduce the delay of salmon passing over dams.