1 May
Cathy Reidy Liermann
Postdoctoral Researcher, UW Aquatic & Fishery Sciences
Ecohydrologic Impacts of Dams: A Global Perspective
Abstract
Despite the recognized importance of natural flow variability for sustaining river ecosystems, people continue to regulate flow regimes in order to meet our needs for water, energy and transport, at increasing magnitudes in many regions of the world. The majority of the world’s large river systems are fragmented and have their flow altered by dams. Exceptions to this tend to lie in regions inhospitable to hydropower development, such as northern tundra, or in the least economically active regions.
The biogeographic distribution of dam impact is widespread, both at terrestrial and freshwater scales, representing significant threat to global biodiversity. Relatively species-poor tundra is the world’s only terrestrial ecoregion which remains predominantly unaffected by dams. Nearly half of the world’s freshwater ecoregions are obstructed by dams, and at least 21 ecoregions are considered heavily obstructed. Synthesis of obstruction data and fish vulnerability traits indicates lampreys (Lampetra spp.), eels (Anguilla spp.) and shad (Alosa spp.) as examples of genera at particular risk of species loss. The most threatened ecoregions span all continents, including the Murray Darling, southern Italy, lower and middle Indus, West Korea, South Atlantic, Upper Paraná and Mobile Bay. Freshwater ecoregions with the highest counts of total and endemic species remain relatively unobstructed, representing conservation potential.
Due to changes in discharge and water stress, the area of large river basins in need of management interventions to protect ecosystems or people will be much greater for basins impacted by dams than for basins with free-flowing rivers. Proactive measures that restore the natural capacity of rivers to buffer climate-change impacts are more desirable than reactive actions since they may lead to benefits which would later be unattainable, such as higher water quality and restored fish populations.
Bio
Cathy Reidy Liermann completed a BMus. at Boston University, her MS in Forest Hydrology here at UW’s College of Forest Resources, and a PhD with the Landscape Ecology group at Umeå University in Sweden. Her doctoral research focused on the ecohydrologic impacts of dams at the global scale, and examined patterns of flow regulation and channel fragmentation by dams in relation to biogeography, socioeconomics and forecasts of global change. She is currently a postdoctoral researcher with Julian Olden here at SAFS, working on flow-ecology relationships for Washington rivers.
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