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Show CEA Report ECOLOGY n[/ f OST OF THE ECOLOGICAL IMPACTS downstream from ' ' I Glen Canyon Dam stem from the loss of sediment and nutrients in the river, loss of natural seasonal fluctuations in the flow of water, change in the temperature of the water released downstream of the dam and introduction of non- native species. The Colorado River is home to one of the most interesting assemblages of fish fauna in North America, due to relative isolation and unique river conditions historically found in the river. Some species have been around for more than 20 million years. Adaptations of the fish to extreme and severe river conditions include large streamlined bodies, large fins, and acute sensory abilities. 30 Current river conditions, as a result of dams, have contributed to the endanger- ment of several native Colorado River fish species. In addition to freshwater fish, birds and other fauna in the lower Colorado River and upper portion of the Sea of Cortez are threatened or endangered, in part, due to the reduced water, sediment and nutrient volume as a result of dams. Red Spotted Toad page 8 Environmental - Ecology General Environment • Flooding has inundated the natural riverine and riparian habitats of Glen Canyon, thereby destroying habitat for hundreds of native species. • The Grand Canyon ecosystem originally formed in a sediment- laden, seasonally fluctuating environment. Construction of Glen Canyon Dam altered this environment and the long- term health of the Grand Canyon ecosystem. Interactions among water volume, temperature, sediment transport and downstream resources support a system quite different from pre- dam conditions. 7 • Prior to construction of the dam, the Colorado River's temperature varied seasonally from 40 to 80 degrees F. Water released from the dam is now a steady 46 degrees F. because water releases come from the cold depths of the reservoir. • Prior to construction of the dam, annual spring floods transported sediments that provided habitat for many native species of fish, amphibians and insects. Now water released from the dam is clear, as sediments are trapped in the reservoir. • The dam has reduced the amount of coarse organic matter reaching Grand Canyon, depleting the level of nutrients necessary for the survival of native species. 6 • Loss of bank- scouring spring floods has allowed non- native riparian plant species to flourish and crowd out native species. 6 Colorado River at the Grand Canyon 0 4 l 1 1 '• 1 1 • ' 0 100 200 300 400 Day of Year Figure 5 Flow of the Colorado River through Grand Canyon in 1946 ( prior to dam construction) and in 1993 showing how dam operations have altered the annual flow cycle ( Myers, 1998). |