8253 - Laserfiche WebLink

Home Browse Search

3 INTRODUCTION Many attributes and functions of lotic ecosystems are partly controlled by the geomorphic organization and processes of the host stream (Power et al. 1988). These geomorphic processes of fluid flow and sediment transport are determined by regional hydrology and sediment yield which in turn are partly controlled by regional geology and geologic history. Channel and floodplain organization may also be controlled by regional geology (Ikeda 1989). Geologic control is prominent in small and intermediate-size watersheds in mountainous terrain, but geologic control may also occur where large rivers cross mountain belts or high plateaus. Large rivers with wide alluvial valleys may display the systematic ecologic, geomorphic, and hydraulic changes in the downstream direction that have been summarized by Leopold and Maddock (1953) and Vannote et al. (1980). However, the geomorphology and ecology of many mountainous intermediate-size streams are strongly influenced by local geology. In the Pacific Northwest, Gregory et al. (1991) describe the linkage between geology and riparian ecosystem function. Nelson et al. (1992) describe the relation among geology, fluvial geomorphology, and the distribution of native cutthroat trout in the North Fork Humbolt River in the Great Basin of Nevada. Few studies, however, have been concerned with influence of geology on the ecosystem function of large rivers. No other river system in the United States is more dominated by its surrounding geology than is the Colorado River; Hunt (1969) stated that the Colorado River crosses more structural barriers than any other river in the Western Hemisphere. The fishery of the Colorado River system also has the greatest degree of endemism of any large drainage basin in the United States; 16 species live only in this drainage basin (Minckley and Deacon, 1991). This combination of unique geological and biological