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Analyzing the impacts of dams on riparian ecosystems: a review of research strategies and their relevance to the Snake River through Hells Canyon.

Braatne JH, Rood SB, Goater LA, Blair CL - Environ Manage (2008)

Bottom Line: As a result, comparative approaches are often correlative and vulnerable to confounding factors.In a case study of Hells Canyon, the upstream versus downstream comparison is confounded by a dramatic geomorphic transition.We conclude that multiple study approaches are essential to provide confident interpretations of ecological impacts downstream from dams, and propose a comprehensive study for Hells Canyon that integrates multiple research strategies.

View Article: PubMed Central - PubMed

Affiliation: Department of Fish and Wildlife Resources, University of Idaho, Moscow, ID 83844, USA.

ABSTRACT
River damming provides a dominant human impact on river environments worldwide, and while local impacts of reservoir flooding are immediate, subsequent ecological impacts downstream can be extensive. In this article, we assess seven research strategies for analyzing the impacts of dams and river flow regulation on riparian ecosystems. These include spatial comparisons of (1) upstream versus downstream reaches, (2) progressive downstream patterns, or (3) the dammed river versus an adjacent free-flowing or differently regulated river(s). Temporal comparisons consider (4) pre- versus post-dam, or (5) sequential post-dam conditions. However, spatial comparisons are complicated by the fact that dams are not randomly located, and temporal comparisons are commonly limited by sparse historic information. As a result, comparative approaches are often correlative and vulnerable to confounding factors. To complement these analyses, (6) flow or sediment modifications can be implemented to test causal associations. Finally, (7) process-based modeling represents a predictive approach incorporating hydrogeomorphic processes and their biological consequences. In a case study of Hells Canyon, the upstream versus downstream comparison is confounded by a dramatic geomorphic transition. Comparison of the multiple reaches below the dams should be useful, and the comparison of Snake River with the adjacent free-flowing Salmon River may provide the strongest spatial comparison. A pre- versus post-dam comparison would provide the most direct study approach, but pre-dam information is limited to historic reports and archival photographs. We conclude that multiple study approaches are essential to provide confident interpretations of ecological impacts downstream from dams, and propose a comprehensive study for Hells Canyon that integrates multiple research strategies.

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Schematic showing general spatial comparisons to analyze environmental impacts downstream from dams. Triangles represent dams and reservoirs
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Fig2: Schematic showing general spatial comparisons to analyze environmental impacts downstream from dams. Triangles represent dams and reservoirs

Mentions: Concept – Probably the most obvious spatial comparison contrasts river reaches upstream versus downstream from a dam and reservoir (Fig. 2, Tables 1 and 2). This comparison is based on the expectation that sequential reaches along a river will experience similar but gradually changing ecological conditions and processes, an expectation consistent with the river continuum concept (Vannote and others 1980). The dam and reservoir separate the upstream versus downstream reaches, which subsequently experience different physical and biological influences (Ward and Stanford 1995a, 1995b). Although upstream and downstream reaches are both impacted by some alterations such as fragmentation of the river corridor (Jansson and others 2000), the upstream reach is unaltered relative to the fundamental fluvial processes of hydrology and sediment flux. There is, consequently, an expectation that the upstream reach will continue to function in a natural manner, similar to the condition without the dam. In contrast, the downstream reach is impacted by aspects such as sediment depletion (Kondolf 1997) and hydrologic changes that reflect the pattern of dam operation. Thus, the upstream versus downstream comparison represents a paired comparison whereby the upstream reach provides the control and the downstream reach represents the treatment condition (Table 2).Fig. 2


Analyzing the impacts of dams on riparian ecosystems: a review of research strategies and their relevance to the Snake River through Hells Canyon.

Braatne JH, Rood SB, Goater LA, Blair CL - Environ Manage (2008)

Schematic showing general spatial comparisons to analyze environmental impacts downstream from dams. Triangles represent dams and reservoirs
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2233706&req=5

Fig2: Schematic showing general spatial comparisons to analyze environmental impacts downstream from dams. Triangles represent dams and reservoirs
Mentions: Concept – Probably the most obvious spatial comparison contrasts river reaches upstream versus downstream from a dam and reservoir (Fig. 2, Tables 1 and 2). This comparison is based on the expectation that sequential reaches along a river will experience similar but gradually changing ecological conditions and processes, an expectation consistent with the river continuum concept (Vannote and others 1980). The dam and reservoir separate the upstream versus downstream reaches, which subsequently experience different physical and biological influences (Ward and Stanford 1995a, 1995b). Although upstream and downstream reaches are both impacted by some alterations such as fragmentation of the river corridor (Jansson and others 2000), the upstream reach is unaltered relative to the fundamental fluvial processes of hydrology and sediment flux. There is, consequently, an expectation that the upstream reach will continue to function in a natural manner, similar to the condition without the dam. In contrast, the downstream reach is impacted by aspects such as sediment depletion (Kondolf 1997) and hydrologic changes that reflect the pattern of dam operation. Thus, the upstream versus downstream comparison represents a paired comparison whereby the upstream reach provides the control and the downstream reach represents the treatment condition (Table 2).Fig. 2

Bottom Line: As a result, comparative approaches are often correlative and vulnerable to confounding factors.In a case study of Hells Canyon, the upstream versus downstream comparison is confounded by a dramatic geomorphic transition.We conclude that multiple study approaches are essential to provide confident interpretations of ecological impacts downstream from dams, and propose a comprehensive study for Hells Canyon that integrates multiple research strategies.

View Article: PubMed Central - PubMed

Affiliation: Department of Fish and Wildlife Resources, University of Idaho, Moscow, ID 83844, USA.

ABSTRACT
River damming provides a dominant human impact on river environments worldwide, and while local impacts of reservoir flooding are immediate, subsequent ecological impacts downstream can be extensive. In this article, we assess seven research strategies for analyzing the impacts of dams and river flow regulation on riparian ecosystems. These include spatial comparisons of (1) upstream versus downstream reaches, (2) progressive downstream patterns, or (3) the dammed river versus an adjacent free-flowing or differently regulated river(s). Temporal comparisons consider (4) pre- versus post-dam, or (5) sequential post-dam conditions. However, spatial comparisons are complicated by the fact that dams are not randomly located, and temporal comparisons are commonly limited by sparse historic information. As a result, comparative approaches are often correlative and vulnerable to confounding factors. To complement these analyses, (6) flow or sediment modifications can be implemented to test causal associations. Finally, (7) process-based modeling represents a predictive approach incorporating hydrogeomorphic processes and their biological consequences. In a case study of Hells Canyon, the upstream versus downstream comparison is confounded by a dramatic geomorphic transition. Comparison of the multiple reaches below the dams should be useful, and the comparison of Snake River with the adjacent free-flowing Salmon River may provide the strongest spatial comparison. A pre- versus post-dam comparison would provide the most direct study approach, but pre-dam information is limited to historic reports and archival photographs. We conclude that multiple study approaches are essential to provide confident interpretations of ecological impacts downstream from dams, and propose a comprehensive study for Hells Canyon that integrates multiple research strategies.

Show MeSH