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4 The State of the Colorado River Ecosystem in Grand Canyon Ouctuated seasonally from 320F to 800F (0-290C) (US. Department of the InteriOl~ 1995). Glen Canyon Dam has changed the seasonal Oow, sediment-carrying capacity, and temperature of the Colorado River. Operation of the dam has altered the frequency of floods on the Colorado River and increased median discharge rates at Lees Ferry, whereas managing for hydroelectric power generation has introduced wide- ranging daily fluctuations (Topping and others, 2003). For example, from 1963 to 1991 (the no action period or historical operations), when the dam was managed primarily to maximize hydroelectric power revenue, it was not uncommon for daily flows to vary from 5,000 to 30,000 cfs (US. Department of the InteriOl~ 1988). Release patterns of this type caused the river level below the dam to change 7-13 ft (2-4 m) per day, creating pub- lic concerns about the quality and safety of fishing and boating and about adverse impacts to natural resources (US. Department of the InteriOl~ 1988). Because the sediment load of the Colorado River is deposited in Lake Powell, water released from Glen Canyon Dam is essentially clear. Furthermore, because the penstocks of the dam are well below the surface of Lake Powell, the water released from the dam is cold, with an average temperature of 460F (80C) (Webb and others, 1999). The construction of Glen Canyon Dam also affected a number of aquatic and terrestrial resources downstream in lower Glen and Grand Canyons. Dam- induced changes in the Colorado River's flow, tempera- ture, and sediment-carrying capacity are blamed for narrowing rapids, beach erosion, invasion of nonnative 11.000 BP Paleo-Indian peoples occupy Grand Canyon region 1893 President Benjamin Harrison creates Grand Canyon Forest Reserve 1869 Major John Wesley Powell leads first recorded expedition to traverse Grand Canyon riparian vegetation, and losses of native fishes (\:Vebb and others, 1999). These same changes are also associated with an increase in total species richness within Grand Canyon National Park; however, the increases are pri- marily for species not originally found in Grand Canyon. Some changes to the ecosystem of the Colorado River, such as the introduction of nonnative fish, were already taking place before the construction of Glen Canyon Dam (Wieringa and Morton, 1996). It is important to note that Glen Canyon Dam was completed before the enactment of the National Environmental Policy Act of 1969 and the Endangered Species Act of 1973 (see timcline). At the time of Glen Canyon Dam's construction (1956-63), little consider- ation was given to how dam operations might affect the downstream environment in Grand Canyon National Park (Babbitt, 1990). Nevertheless, public values were undergoing a shift: at the same time that Congress autho- rized Glen Canyon Dam in 1956, authorization of Echo Park Dam on the Green River was defeated because of environmental reasons (Ingram and others, 1991). Federal Efforts to Protect Grand Canyon The international prominence of Grand Canyon National Park and public concern about the impacts of Glen Canyon Dam caused the Bureau of Reclamation in 1982 to undertake a science program, Glen Canyon 1908 President Theodore Roosevelt creates Grand Canyon National Monument 1916 National Park Service Organic Act passed \)~?~RitAENT OF THE INrE. ~~~o~ 1902 Reclamation Act creates the Bureau of Reclamation . - --~: