USGS Publications Warehouse

Abstract

IntroductionIn 1990, the U.S. Geological Survey (USGS), in cooperation with the Idaho Department of Environmental Quality (IDEQ), implemented a statewide water-quality monitoring program (SWQP) in response to Idaho?s antidegradation policy as required by the Clean Water Act (Clark, 1990). The program objective was to provide water-quality managers with a coordinated, statewide network to detect trends in surface water quality. A consistent, integrated assessment of water quality will provide water managers, policy makers, and the public with an improved scientific basis for evaluating effectiveness of water-quality management programs in principal river basins throughout Idaho. Human activities can alter the physical, chemical, or biological processes of surface water. Such alter-ations, in turn, can cause changes in the resident aquatic biological assemblages. Monitoring the health of these assemblages can complement other physical and chemical water-quality assessment methods and, thus, can provide a more complete evaluation of water resource conditions (Karr, 1991). According to Allan and Flecker (1993), protecting or managing ecosystems and associated biological diversity requires development of ways to monitor ecosystem health. Measuring changes in fish, macroinvertebrate, and algal assemblages can provide an index of water quality and trends that affect beneficial uses of surface-water resources, detect problems that other methods might miss or underestimate, and provide a systematic process for measuring progress of pollution abatement programs (Intergovernmental Task Force on Monitoring, 1995). Macroinvertebrates have been used extensively to assess the status and trends of aquatic life in rivers. Hardy and others (1995) reported trends in benthic invertebrates, along with other physical and chemical measures of stream water quality, for a cooperative program between the USGS and Chester County, Pennsylvania. Maret (1995) summarized a number of studies that have used macroinvertebrates to assess water quality of streams in the upper Snake River Basin. Macroinvertebrates inhabit most streams and are a key component in processing of organic material and in nutrient cycling and are an important food source for fish and other aquatic organisms. These organisms are easy to collect, relatively sessile, and have specific environmental requirements to complete their life cycle. Macroinvertebrate assemblages are excellent indicators of long-term environmental changes such as siltation (Lenat and others, 1981) and point-source pollutants of short duration (Prophet and Edwards, 1973). Macroinvertebrates integrate the effects of upstream land and water uses in a basin over the long term (months to years) because most of their life cycle is spent in the water. Use of biological attributes, or metrics, to describe water quality is increasing. Recent State and Federal program developments in biological monitoring have emphasized more direct measures of biotic integrity to assess beneficial use status and trends (Plafkin and others, 1989; Hayslip, 1993). A metric is an enumeration representing an assemblage characteristic or combination of characteristics that changes in a predictable way with increased human influence (Karr and others, 1986). Several macroinvertebrate indices using a variety of metrics have been developed in the Northwest as tools to help evaluate water quality and biotic integrity. Among these are an index identifying urban effects in the Puget Sound Lowlands in Washington (Kleindl, 1995), forestry effects in Oregon (Fore and others, 1996), and an evaluation of least-disturbed small streams in the Cedar River watershed of Washington (Black and MacCoy, 2000). The IDEQ recently has developed biological monitoring protocols to assess beneficial uses of medium and large rivers (Grafe, 2000) based, in part, on studies by the Idaho State University, Stream Ecology Center (Royer and Minshall, 1996; Royer and others, 2001). In addition, the USGS, through the National Water-Quality Assessment (NAWQA) Program, has included comprehensive monitoring protocols to assess aquatic life and associated habitat quality (Gurtz, 1994). These studies have shown that aquatic biological assemblages are effective integrators of stream conditions, including chemical and habitat changes that have resulted from human activities in river basins. Therefore, evaluation of these assemblages can be useful in assessing biotic integrity and associated designated beneficial uses such as coldwater biota and salmonid spawning. The Idaho SWQP, which began with a focus on water chemistry, was expanded in 1996 to a more integrated monitoring network that included biological information to more effectively assess instream beneficial uses. Major components of this assessment were the collection of aquatic macroinvertebrates from a variety of stream habitats and measurement of associated environmental variables. Two assessment approaches were used to evaluate the macroinvertebrate data collected from Idaho rivers ?biological metrics and multivariate statistical analyses. First, biological metrics relate specific measures of assemblage structure, composition, and functional attributes to a minimally disturbed system (Karr and others, 1986). The metric approach is dependent on regional biological and environmental reference information to score individual metrics (Miller and others, 1988). A metric score can be used as a single numeric index, such as the number of species (or taxa), or combined into a comparative rating of multiple metrics, such as U.S. Environmental Protection Agency?s (USEPA) rapid bioassessment protocols (Plafkin and others, 1989; Barbour and others, 1999). The multimetric approach has been advocated because several metrics, each measuring a different component of the assemblage, are believed to provide a more robust assessment of ecological integrity (Fore and others, 1996). The biological metrics approach also is most amenable to nonexperts. In this study, the multimetric approach will be evaluated. Second, ecologists have used multivariate analyses to identify and interpret patterns in macroinvertebrate assemblage structure as they relate to environmental conditions (Gauch, 1982; Richards and others, 1993; Frenzel, 1996). These multivariate analyses summarize patterns of association within a species-by-sample data matrix for purposes of classification. Multivariate analyses are effective for identifying similarities among sites with respect to various physical, chemical, and biological characteristics and for depicting relations between assemblage patterns and environmental gradients. Hypotheses also can be formulated from these exploratory analyses about relations between macroinvertebrate assemblages and environmental variables. Few studies have examined relations between macroinvertebrate assemblages and measured environmental variables across the major environmental settings of Idaho. Most macroinvertebrate studies have been conducted on small, wadeable streams (fourth order or less, after Strahler, 1957); large-river studies remain limited. Robinson and Minshall (1998) studied wadeable streams across three major ecoregions of Idaho. Mebane (2001) studied relations among macroinvertebrate metrics, fine-grained sediment, and metals in wadeable streams across four ecoregions of Idaho. Royer and Minshall (1996) and Royer and others (2001) sampled a number of medium- to large-river sites for IDEQ to develop multimetric indices using macroinvertebrates. They developed an invertebrate river index (IRI) that appears to function well as a bioassessment tool for both medium and large rivers in Idaho. However, their index consisted of only 22 sites and 6 validation sites from rivers across Idaho. The investigation documented in this report offers an independent evaluation of the IRI encompassing a wider variety of medium- to large-river sites and environmental conditions by using similar collection methods but a different laboratory for taxonomic processing. In addition, a number of basin-level variables were determined with a geographic information system (GIS) to assess landscape-scale influences, such as basin area and land-use variables, on macroinvertebrate assemblages. These quantitative measures of basin and habitat data facilitate evaluation of metric responsiveness to multiple measures of impairment, as well as to natural influences on macroinvertebrate assemblages.