Fundamental Elements of Ecologically Healthy Watersheds in the Pacific Northwest Coastal Ecoregion

Abstract

Abstract. InCharacteristics of streams and rivers reflect variations in local geomorphology, climatic gradients, spatial and temporal scales of natural disturbances, and the dynamic features of the riparian forest. This results in a variety of stream types which, when coupled with the many human uses of the Pacific Northwest coastal ecoregion, presents a difficult challenge in identifying and evaluating fundamental, system-level components of ecologically healthy watersheds. Over 20 types of streams are found in western Oregon, Washington, and British Columbia and in southeastern Alaska, a region where extractive forest, agricultural, fishing, and mining industries and a rapidly increasing urban population are severely altering the landscape. Yet stream characteristics remain the best indicators of watershed vitality, provided the fundamental characteristics of healthy streams are accurately known. The premise of this article is that the delivery and routing of water, sediment, and woody debris to streams are the key processes regulating the vitality of watersheds and their drainage networks in the Pacific Northwest coastal ecoregion. Five fundamental components of stream corridors are examined: basin geomorphology, hydrologic patterns, water quality, riparian forest characteristics, and habitat characteristics. Ecologically healthy watersheds require the preservation of lateral, longitudinal, and vertical connections between system components as well as the natural spatial and temporal variability of those components. The timing and mode of interdependencies between fundamental components are as important as the magnitude of individual components themselves.

Creating a catchment scale perspective for river restoration

“…The processes and landforms that comprise the fluvial landscape vary with location in a catchment governed by hillslope and valley topography, river network structure, channel elevation profiles, basin scale, and the stochastic nature of climate (Frissel and Nawa, 1992;Reeves et al, 1995;Naiman et al, 1992;Poff et al, 1997;Benda et al, 1998;Ward et al, 2002). The fluvial landscape is thus a dynamic entity, formed and altered over time by the storms, erosion and floods that bring water, sediment and organic material downslope and downstream from all points in a catchment.…”

The Role of Riparian Corridors in Maintaining Regional Biodiversity

“…Consequently, plant species richness varies considerably in space and time along stream margins, and these variations have important influences on the in-stream biota and processes. It is well known that riparian vegetation regulates light and ternperature regimes, provides nourishment to aquatic as well as terrestrial biota, acts as a source oflarge woody debris (which significantly influences sediment routing, channel morphology and in-stream habitat), regulates the flow of water and nutrients from uplands to the stream, and maintains biodiversity by providing an unusually diverse array of habitat and ecological services (Naiman and Decamps 1990). We believe that many of the ecological issues related to landuse and environmental quality could be ameliorated with effective riparian corridor management.…”

Grays River Watershed and Biological Assessment Final Report 2006.

“…A watershed-based approach encompasses almost all of the critical components of the freshwater ecosystem that supports native salmonid species. It has been widely recognized that restoration and conservation measures developed in a watershed-ecosystem context are more likely to be successful (Nehlsen et al 1991;Reeves et al 1991Reeves et al , 1995Naiman et al 1992Naiman et al , 1995Doppelt et al 1993;FEMAT 1993;Lichatowich et al 1995;Beechie et al 1996Frissell and Bayles 1996;Stouder et al 1997;Williams et al 1997;Beechie and Bolton 1999;Pess et al 1999Pess et al , 2002Pess et al , 2003.…”

“…Roads also cause more rapid and more frequent "gully" (erosional) channel development (Wemple et al imber-harvest activities, including clear-cut logging and road construction, have been shown to h n 1979; Harr 1986;Naiman et al 1992;LaM t al. 20 ve for of flood ds af f researc in runoff from clear-cut areas as compared to areas of mature coniferous forest (Harr 1981(Harr , 1986Harr et al 1982).…”

“…According to Bayley (1995), the floodplain is that part of the river floodplain ecosystem that is regularly flooded and dried, and it represents a type of wetland. Well-developed, complex floodplains are characteristic in large river systems where there are long periods of seasonal flooding, oxbow lakes, wetlands, a diverse forest community and moist soils (Gregory et al 1991;Naiman et al 1992;Poff et al 1997;Naiman and Bilby 1998). Flood events of different size and frequency play a vital role in maintaining a diversity of riparian plant species and aquatic habitat (Junk et al 1989;Poff et al 1997;Swanson et al 1998).…”