Ecological Considerations for Stream Projects
K. L. Boyer. USDA Natural Resources Conservation Service, Wildlife Habitat Management Institute, Department of Fisheries and Wildlife,104 Nash Hall, Oregon State University, Corvallis, OR 97330
The NRCS Stream Design Guide provides guidance for teams of engineers, biologists, geomorphologists, hydrologists, landowners, and resource managers who are planning and designing projects intended to improve streams, and how they function. Specific stream project goals may include controlling floods or sediment sources, hastening drainage, stabilizing banks, improving fish habitat, or restoring the ecological functions and processes of a stream and its floodplain. Many approaches and techniques can be used to reach these goals, but recognition of the living and nonliving components of the stream ecosystem, its watershed, how they interact and affect each other, and the timeframes over which stream processes occur will improve the probability of desirable outcomes. The chemical and biological processes that occur within stream corridors, and between them and adjacent lands, are intricate and involve numerous linkages and feedback loops. Accordingly, this paper provides a brief overview of current knowledge regarding stream ecosystem processes and functions important to consider when designing stream improvements. Topics to be presented will include (1) ecological responses to movement of water
and materials, longitudinal and lateral adjustment of channels, and floodplain alterations; (2) key ecological processes critical to aquatic community dynamics; (3) types of stream corridor habitats; and (4) the relative importance of disturbance in sustaining aquatic communities. KEYWORDS. Aquatic, flooding, restoration, stream corridor, streams, riparian, rivers.
Natural or minimally-altered stream corridors tend to be physically heterogeneous regardless of their size. Fluxes of energy, water and materials that occur throughout the stream corridor system create a dynamic and complex three-dimensional (length, width, depth) mosaic of different habitats and physical features, changing through time and contributing to the high level of biological diversity typical of stream corridors. The interactions occurring among the different elements of stream corridors are extensive and reciprocally obligatory for many of the plant and animal species that inhabit or use them. Human activities in stream corridors often simplify physical structure (for example, by removing riparian vegetation) or fragment connections among their components (such as that between the stream and its floodplain), preventing or limiting natural processes important to many species. Projects designed to restore or maintain the ecological linkages of stream corridors, and their physical connections, are promising approaches for arresting the decline of aquatic and riparian species, and improving water quality. However, the complex physical, biological, and social nature of stream corridors creates a challenge to professionals responsible for improving stream functions and conditions. Systems with more intact natural flow regimes are very complex. From a human perspective, they are also less predictable and potentially risky. Recent studies in stream ecology emphasize the
importance of linkages between stream channels, riparian areas, and floodplains (Gregory et al. 1991, Stanford and Ward 1992, Brookes et al. 1996, Huggenberger et al. 1998, Molles et al. 1998). Stream corridor projects that integrate the disciplines of fluvial geomorphology, hydrology, aquatic and riparian ecology, and hydraulic and geotechnical engineering are more effective at meeting multiple objectives that address economic and ecological considerations.
A watershed captures precipitation, filters and stores water, and regulates its release through a channel network into a lake, another watershed, or an estuary...
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