Nitrogen Supersaturation Levels Below Ridgway Reservoir, Colorado: Causes and Remedies

Project ID: 581
Principal Investigator: Glenn Stone
Research Topic: Ecosystem Needs
Funded Fiscal Years: 2004 and 2005
Keywords: None

Research Question

* What tests can be performed to determine a relationship between Ridgway Dam discharge and nitrogen levels below the outlet works?

* What levels of nitrogen supersaturation are observed in the downstream fishery?

* What effective engineering techniques can be used to reduce the effects of nitrogen supersaturation on the downstream fishery?

Need and Benefit

In 1998, the Colorado Division of Wildlife, during routine fish shocking activities immediately downstream of Ridgway Dam, recovered fish which showed evidence of gas bubble disease. Gas bubble disease in fish is the result of elevated levels of dissolved gas (specifically supersaturated nitrogen) in the water in which the fish habitat.

Gas bubble disease is similar to the "bends" that occurs to divers--the fish actually get bubbles inside their bodies, as well as on their fins, skin, and eyes. Gas bubble disease is a poorly understood problem associated with dams, and resident fish can easily become victim to gas bubble disease almost without notice. It is thought that most of the fish that die from the disease sink and are never seen. Others are eaten by predators, or may suffer sub-lethal effects and be more susceptible to other diseases. Some fish are able to release the trapped gas in their system, while others show the bubble effect on their bodies.

Reclamation has gone to great effort and expense to develop the Uncompahgre River immediately below Ridgway Dam into a very popular, catch-and-release, quality fishing area. This fishing area is located in western Colorado's largest and most frequently visited state park. This fishing area is well publicized and highly promoted; however, the quality of fishing has not reached its potential. Gas bubble disease has been identified as the most likely cause of the problem.

The research project would evaluate the extent of the gas bubble disease problem (nitrogen supersaturation) downstream of Ridgway Dam, identify the cause of the dissolved gas, and propose solutions to the problem.

A goal of the research is to develop new information and technological remedies to address nitrogen supersaturation downstream of Ridgway Dam, which also could potentially be applied at other Reclamation dams--or any other dams. Nitrogen supersaturation problems have already been identified at several other Reclamation dams throughout the Western United States. The research would focus on operational changes and/or development of innovative structural modifications that would be the most cost effective, but in the most environmentally sound manner.

Another goal of the research is to demonstrate Reclamation's responsiveness to addressing a potential problem. By anticipating the long-term adverse effects on the downstream fishery caused by current operation or structural design, Reclamation has an opportunity to correct a potential problem and protect a fishery of regional importance that the public has valued and enjoyed for the last 15 years.

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Last Updated: 4/4/17