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Ecohydrologic impacts of dams: A global assessment
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This dissertation aims to improve our understanding of how dams and reservoirs impact freshwater systems worldwide. The following questions were addressed specifically: 1) what are the spatial patterns and magnitudes of flow regulation and channel fragmentation by dams globally; 2) how are dam impacts distributed biogeographically, and which are the biogeographic regions and taxa most threatened by dam impacts; and 3) how can climate change and dams be expected to interact in basins, and what management actions would mitigate adverse interactions? Results show that 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 internally fragmented by dams, and ecoregional distinctions may be artifically imposed by dams in many cases. Freshwater ecoregions with the highest counts of total and endemic species remain relatively unobstructed, representing significant conservation potential. Diadromy is one of the few fish traits indicative of vulnerability to dams for which data are sufficient for global scale analysis. Lampreys (Lampetra spp.), Eels (Anguilla spp.) and Shad (Alosa spp.) are examples of genera particularly vulnerable to dams because their distributions coincide with the most heavily fragmented freshwater ecoregions, and a large proportion of the coincident species for each genera are diadromous. 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 also lead to environmental benefits such as higher water quality and restored fish populations – benefits which may later be unattainable.

Place, publisher, year, edition, pages
Umeå: Ekologi, miljö och geovetenskap , 2007. , 17 p.
Keyword [en]
dam; reservoir; river regulation; flow alteration; fragmentation; freshwater biodiversity
National Category
Oceanography, Hydrology, Water Resources
URN: urn:nbn:se:umu:diva-1394ISBN: 978-91-7264-429-8OAI: diva2:140870
Public defence
2007-11-09, 5, Uminova Science Park, Tvistevägen 48, Umeå, 10:00 (English)
Available from: 2007-10-18 Created: 2007-10-18 Last updated: 2012-07-09Bibliographically approved
List of papers
1. Fragmentation and flow regulation of the world's large river systems
Open this publication in new window or tab >>Fragmentation and flow regulation of the world's large river systems
2005 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 308, no 5720, 405-408 p.Article in journal (Refereed) Published
Abstract [en]

A global overview of dam-based impacts on large river systemsshows that over half (172 out of 292) are affected by dams,including the eight most biogeographically diverse. Dam-impactedcatchments experience higher irrigation pressure and about 25times more economic activity per unit of water than do unaffectedcatchments. In view of projected changes in climate and waterresource use, these findings can be used to identify ecologicalrisks associated with further impacts on large river systems.

Biodiversity, Ecosystem, Geography, Human Activities, Rivers, Trees, Water Movements
National Category
Natural Sciences
urn:nbn:se:umu:diva-7688 (URN)10.1126/science.1107887 (DOI)15831757 (PubMedID)
Available from: 2008-01-11 Created: 2008-01-11 Last updated: 2013-10-04Bibliographically approved
2. Climate change and the world's river basins: anticipating management options
Open this publication in new window or tab >>Climate change and the world's river basins: anticipating management options
Show others...
2008 (English)In: Frontiers in Ecology and the Environment, ISSN 1540-9295, Vol. 6, no 2, 81-89 p.Article in journal (Refereed) Published
Abstract [en]

Major rivers worldwide have experienced dramatic changes in flow, reducing their natural ability to adjust to and absorb disturbances. Given expected changes in global climate and water needs, this may create serious problems, including loss of native biodiversity and risks to ecosystems and humans from increased flooding or water shortages. Here, we project river discharge under different climate and water withdrawal scenarios and combine this with data on the impact of dams on large river basins to create global maps illustrating potential changes in discharge and water stress for dam-impacted and free-flowing basins. The projections indicate that every populated basin in the world will experience changes in river discharge and many will experience water stress. The magnitude of these impacts is used to identify basins likely and almost certain to require proactive or reactive management intervention. Our analysis indicates that the area in need of management action to mitigate the impacts of climate change is much greater for basins impacted by dams than for basins with free-flowing rivers. Nearly one billion people live in areas likely to require action and approximately 365 million people live in basins almost certain to require action. Proactive management efforts will minimize risks to ecosystems and people and may be less costly than reactive efforts taken only once problems have arisen.

National Category
Ecology Environmental Sciences
urn:nbn:se:umu:diva-11478 (URN)10.1890/060148 (DOI)
Available from: 2009-01-09 Created: 2009-01-09 Last updated: 2014-03-13Bibliographically approved
3. Implications of dam obstruction for global freshwater fish diversity
Open this publication in new window or tab >>Implications of dam obstruction for global freshwater fish diversity
2012 (English)In: BioScience, ISSN 0006-3568, E-ISSN 1525-3244, Vol. 62, no 6, 539-548 p.Article in journal (Refereed) Published
Abstract [en]

Dams are obstructing rivers worldwide, impairing habitat and migration opportunities for many freshwater fish species; however, global data linking dam and fish distributions have been limited. Here, we quantify dam obstruction at the biogeographic scale of freshwater ecoregion, which provides the spatial framework necessary to assess the risk of fish species loss due to dams and allows us to identify both ecoregions and genera at risk. Nearly 50% of the 397 assessed freshwater ecoregions are obstructed by large- and medium-size dams, and approximately 27% face additional downstream obstruction. A synthesis of obstruction data and fish traits indicates that taxa such as lampreys (Lampetra spp.), eels (Anguilla spp.), and shads (Alosa spp.) are at particular risk of species loss. Threatened ecoregions with heavy dam obstruction and above-average counts of total, diadromous, or endemic species are found on all continents and include the Murray-Darling Province, Southern Italy, the Lower and Middle Indus Basin, West Korea, the South Atlantic region of the United States, the Upper Parana, and Mobile Bay ecoregions.

National Category
Zoology Environmental Sciences
urn:nbn:se:umu:diva-2644 (URN)10.1525/bio.2012.62.6.5 (DOI)000305262500005 ()

Manuscript version included in dissertation with title "Dam obstruction among the world's freshwater ecoregions and implications for global freshwater fish diversity"

Available from: 2007-10-18 Created: 2007-10-18 Last updated: 2013-10-03Bibliographically approved

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