An Analysis of Stream Habitat Conditions in Reference and Managed Watersheds on Some Federal Lands within the Columbia River Basin

—The loss of both habitat quality and quantity for anadromous fish in the Columbia River basin has been identified as a major factor in the decline of many species and has been linked to a variety of land management activities. In this study, we compared stream reaches in watersheds representing both managed and reference conditions to determine whether we could detect differences in physical habitat variables. We divided stream habitat measures into three components: stream banks, instream habitat (pools and pool depth), and stream substrate. We randomly sampled perennial streams within 261 sixth hydrologic unit code (HUC) stream reaches on federal lands in Idaho, Montana, Oregon, and Washington. The sample population represented stream reaches in 62 reference watersheds and 199 managed watersheds. An unbalanced, incomplete-block-design analysis of covariance (ANCOVA) was performed on each of the habitat variables using geology type as the block effect and bank-full width, stream gradient, and average precipitation as the covariates. Watersheds containing reference stream reaches had a slightly higher percentage of federal lands, were smaller, tended to occur at higher mean elevations, and received more annual precipitation than did the managed watersheds. We observed differences in most measures of stream habitat between reference and managed watersheds, generally in the direction we expected. Stream banks were more stable and more undercut in reference stream reaches. Pools in reference stream reaches were deeper than pools in managed stream reaches and had less fine sediment in pool tails. Analysis of covariance was an effective way to compare data across a large, relatively heterogeneous landscape where sample site stratification may be impractical or sample sizes are limited. We believe that the comparison of reference conditions to conditions across managed landscapes provides a credible way to report on the condition of these systems in lieu of trend information at individual sites. The decline of native fish species in western North America has prompted renewed interest in monitoring the relationships between land management activities and aquatic and riparian ecosystems. The loss of both habitat quality and quantity for anadromous fish in the Columbia River basin has been identified as a major factor in the * Corresponding author: [email protected] Received January 8, 2004; accepted March 30, 2004 decline of many species (U.S. Forest Service and Bureau of Land Management 1995). Improvement in stream habitat has been recommended as one of the primary steps in the recovery of fish populations within the basin (National Marine Fisheries Service 1995; U.S. Forest Service and Bureau of Land Management 1995; Kareiva et al. 2000) The decline of stream habitat quality and quantity in the basin has been linked to a variety of land management activities including livestock grazing, road construction, agriculture, urbaniza1364 KERSHNER ET AL. tion, timber harvest, and mining. Changes in stream habitat are generally thought to be a consequence of improper management or implementation of these activities. The consequences of these activities are often reported as changes in stream habitat, water quality, hydrology, riparian vegetation, and aquatic biota. The suite of physical changes that result from land use impacts are manifested in three major components of stream habitat: the stream banks, the stream channel, and the stream substrate. Studies examining the influence of livestock grazing have used variables that measure changes in stream banks, including bank angle (Platts 1991; Knapp and Matthews 1996), the percent and depth of undercut banks (Myers and Swanson 1995; Knapp and Matthews 1996), and bank stability (Kauffman et al. 1983; Platts and Nelson 1985; Myers and Swanson 1992). Variables used to evaluate changes in the stream channel include the width of the stream (Kauffman et al. 1983; Platts et al. 1983; Matthews 1996); the change in the distribution, type, and morphology of channel units (Marcuson 1977; Hubert et al. 1985; Myers and Swanson 1996); and changes in channel form (Marcuson 1977). Changes in substrate include increases in fine sediment (Hubert et al. 1985; Myers and Swanson 1996), reduced spawning habitat (Duff 1983), and changes in riffle particle sizes (Kappeser 2002). Studies evaluating changes in stream habitat from logging, road construction, mining, and other activities have used variables similar to those used in grazing studies, but may be more focused on the consequences of a particular activity. For example, the consequences of poor timber harvest practices or improper road design or construction may be more related to changes in large woody debris and sediment supply. Variables that have been used to assess these changes have included the amount and depth of large pool habitat (Woodsmith and Buffington 1996; McIntosh et al. 2000), the volume of fine sediment in pools (Lisle and Hilton 1992), riffle armoring (Kappeser 2002), and the alteration of large woody debris input (Bisson et al. 1987; Woodsmith and Buffington 1996). Studies of land use effects have been conducted at a variety of scales. Grazing effects studies typically involve a comparison of riparian and stream habitat changes that occur when cattle are excluded from certain sections of streams (Duff 1977; Platts 1991; Magilligan and McDowell 1997). Long-term differences in riparian and stream habitat within an exclosure can serve as a reference point for the direction and rate of recovery of these systems once livestock are removed. Disadvantages of these studies are that they are often of limited value because the exclosures are too small, poorly located, or not replicated (Rinne 1999; Sarr 2002). Long-term, whole-watershed studies can be used to track the consequences of a management manipulation through a stream network over a longer time. These studies provide insights into the extent of the perturbation(s) and the duration of the effect on the stream. For example, long-term (.20 years) studies in Carnation Creek, British Columbia, indicated that logging and road building have increased landslides and debris torrents that have altered stream channels and habitat, ultimately reducing the quality of spawning and rearing habitat for salmonids (Hartman et al. 1996). A potential drawback of these types of studies is that results may not be applicable to broader scales. Although some inferences about changes in process and function can be made, differences in climate, elevation, precipitation regime, and vegetation type may limit the ability to extrapolate results from single sites to other areas. Studies that are conducted across multiple stream reaches or watersheds may provide insights at a broader scale (Ralph et al. 1994; Woodsmith and Buffington 1996). Woodsmith and Buffington (1996) compared stream habitat in watersheds with extensive timber harvest and watersheds with no harvest in 23 forest stream reaches in southeast Alaska. They found that they could discriminate their ‘‘reference’’ watersheds from the managed watersheds by differences in three measures of stream habitat: total numbers of pools per reach, ratio of mean residual pool depth to mean bankfull depth, and the ratio of critical sheer stress of the median surface grain size to bank-full sheer stress. Variability and range in pool frequencies were unchanged in streams representing ‘‘natural’’ streams, but decreased during the 1930s to the 1990s in the Columbia River basin (McIntosh et al. 2000). Inferences from these types of studies are often extrapolated to larger geographic areas to imply the consequences of land management, but few studies are specifically designed for that purpose. Larger scale monitoring studies that track the change in habitat condition over time may allow for the regional detection of responses that are due to changes in management (Urquhart et al. 1998; Larsen et al. 2001). For example, the Environmental Monitoring and Assessment Program (EMAP) has proposed regional monitoring efforts 1365 AN ANALYSIS OF STREAM REACH HABITAT that attempt to detect change in environmental conditions over the United States (Whittier and Paulsen 1992; Larsen et al. 1995). Change detection requires periodic revisits to the same sites to observe both the direction and magnitude of change. In some cases, the period of time to detect change may take from 5 to 20 years, depending on the design and variables of interest (Urquhart et al. 1998). Managers often have a need for more rapid assessment of environmental conditions in lieu of repeated visits to the same site. One way to look at differences is to evaluate conditions between sites impacted by some form of management and sites that have relatively intact physical and biological processes. Regional reference sites may also be a way to evaluate the potential of streams within the same region (Karr and Dudley 1981; Hughes et al. 1986). Classification systems have been developed to evaluate the impairment of water quality based on the conditions of reference sites in Australia and Great Britain (Moss et al. 1987; Wright et al. 1993; Wright 1995) and are currently being used to assess water quality condition in the United States (Hawkins et al. 2000). One difficulty with using this approach is that the number and quality of reference sites may be limited in certain locations. In this study, we examined stream reaches in watersheds representing both managed and reference conditions to determine if we could detect differences in physical habitat variables. This work is part of a broader study to evaluate whether aquatic and riparian conditions are being maintained, degraded, or restored on federal lands administered by the U.S. Forest Service and the Bureau of Land Management in the Columbia basin (Kershner et al. 2004). Our objectives were to describe differences in commonly measured stream habitat variables between reference and managed stream reaches and to evaluate the usefulness of these variables in measuring change in this analysis.