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138 The Effects of Dams and Flow Management on Columbia River Ecosystem Processes Chris Peery Introduction The Columbia River is a dominating ecological feature of the Pacific Northwest. This river, second largest in the U.S., encompasses a basin containing much of the states of Oregon,Washington, and Idaho, and parts of Montana, Utah,Wyoming, Nevada, and British Columbia, Canada: about 660,500 square kilometers. It has physically shaped the regional landscape for millennia. Relatively speaking, the influence of the Columbia River on human culture and economy has spanned much less time, both pre- and post-European settlement, but the effects have been no less dramatic. Iconic of the Columbia River have been the remarkable runs of anadromous Chinook salmon (Oncorhynchus tshawytscha), believed to be the largest in the world historically, and steelhead (O. mykiss) that returned each year. But the system also supported sizable populations of coho (O. kisutch), sockeye (O. nerka), chum (O. keta) and pink (O. gorbuscha) salmon, anadromous Pacific lamprey (Lampetra tridentata), white and green sturgeon (Acipenser transmontanus; A. medirostris), and burbot (Lota lota) among many other aquatic species. Many of the existing salmon populations within the Pacific Northwest are also relative newcomers, likely developing since the retreat of the last ice event, approximately 16,000 years ago (Waples et al. 2009). There is no real way to know, but estimates range from six to as many as sixteen million salmon returning to the Columbia River basin historically (Northwest Power Planning Council 1986). Most salmonid populations have been reduced significantly, with only a handful of populations considered healthy or even selfsustaining without significant management intervention. Return of all salmon to the Columbia River now is closer to one million annually and 80 to 90 percent of these are believed to be the result of hatchery production (National Research Council 1996). Decline of our salmon populations has been an obvious manifestation of the changes humans have wrought to the Columbia Basin. Causes for the declines have been much debated, as have methods to conserve and restore salmon populations. Significant resources have been devoted to salmon-related mitigation, research, and recovery efforts. Much of this work revolves around the The Effects of Dams and Flow Management on Ecosystem Processes 139 use of technology to raise fish at hatcheries and to improve survival of juvenile and adult life stages as they migrate between freshwater spawning and juvenile rearing habitats (includes hatcheries) and marine areas where the bulk of growth occurs (Ruckleshaus et al. 2002). Unfortunately, after several decades of this effort, costing into the billions of U.S. dollars (General Accounting Office 2002), little improvement in salmon production within the basin has been realized.As a result, there is a renewed interest by the governments of the U.S. and Canada as well as scientists and scholars to understand the underlying causes of salmon decline and the factors that limit salmon production.One response has been a movement to use an ecosystem view of the Columbia River and the processes that maintain system functions (Williams 2006; Bottom et al. 2009). The System The ecosystem encompasses all the separate components that make up our environment. Ecosystem components are physical (landscape and climate) and biological (microbes,plants,animals).Although there may be a tendency to think of rivers primarily as water flowing through a channel, the river ecosystem comprises everything within the watershed.From the perspective of the salmon,the watershed consists of (at least), (1) the riverine section—wetted channel ranging from small headwater streams to the estuary and associated microhabitat features (pools, riffles, runs,large woody debris (LWD),etc.,) (2) riparian zone and flood plain—the cross sectional characteristics of stream valley with associated plants and animals, and (3) the hyporheic zone—areas where water flows through substrate of the flood plain. The latter influences base flows, nutrient dynamics, and temperature (Ward 1989). Although not physically included within the Columbia River Basin, we can add the ocean as a fourth component to the ecosystem when dealing with anadromous salmon. Aquatic systems are inherently dynamic, driven by cyclical and chaotic forces that work at a range of spatial and temporal scales.These drivers are the ecosystem processes that guide interactions between the physical and biological components and maintain functioning systems. In the Columbia River, the primary physical processes are discharge and temperature (i.e., Climate) and their interaction with underlying geology and geography. These in turn affect sediment and nutrient supply and riparian and floodplain characteristics (Waples et al.2009...


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