Habitat is defined as the environment in which the life needs of a plant or animal are supplied. River habitat features are not static; rather, they are dynamic, changing, and evolving as human and natural factors affect fluvial processes. These processes can have profound effects on biological diversity and ecological integrity within a river basin. River-restoration efforts have frequently focused on returning aquatic habitats to their natural condition. However, present or intended (future) beneficial uses of rivers might or might not be met by the original, natural habitat condition. For example, we know relatively little about historical instream and riparian habitat conditions (or biological diversity) in the South Platte River and how those conditions might support desired human uses (recreation, fishing, aesthetics) in the future. Without establishing a frame of reference for habitat and its ecological links, claims of deterioration of biological diversity and ecological integrity might be impossible to judge and difficult to predict. Although habitat considerations are recognized as important by many local, state, and federal agencies, quantitative procedures for assessing the quality and integrity of aquatic habitats have not been evaluated, and relations between qualitative habitat assessments and biological diversity are poorly understood.
Stream habitat is characterized in the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program as part of an integrated physical, chemical, and biological assessment of the Nation's water quality. The South Platte River Basin NAWQA Study Unit is assessing environmental settings and the relation of stream habitat to several factors that could be used to describe existing water-quality conditions. Evaluation of stream habitat is based on a spatially hierarchical framework that incorporates habitat data at basin, segment, reach, and microhabitat scales. This framework provides a basis for local and national consistency in collection techniques. Quantitative habitat evaluations were done yearly at 11 sites in the South Platte River basin during 1993-1995, and included measurements of more than 34 riparian and instream habitat characteristics. Detailed surveys of channel cross-sections at those sites were done in 1994 and 1995. Integration of quantitative habitat characteristics with current water-quality conditions and biological diversity could form an important basis for guiding river-restoration efforts in the South Platte River basin.
1 U.S. Geological Survey, Box 25046, MS 415, Denver Federal Center, Lakewood, CO 80225