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Scientific Investigations Report 2010–5148

Prepared in cooperation with the Colorado River Water Conservation District, Eagle County, Eagle River Water and Sanitation District, Upper Eagle Regional Water Authority, Colorado Department of Transportation, City of Aurora, Town of Eagle, Town of Gypsum, Town of Minturn, Town of Vail, Vail Resorts, Colorado Springs Utilities, Denver Water, and the U.S. Department of Agriculture Forest Service

Macroinvertebrate-Based Assessment of Biological Condition at Selected Sites in the Eagle River Watershed, Colorado, 2000–07

By Robert E. Zuellig, James F. Bruce, Brian D. Healy, and Cory A. Williams

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The U.S. Geological Survey (USGS), in cooperation with the Colorado River Water Conservation District, Eagle County, Eagle River Water and Sanitation District, Upper Eagle Regional Water Authority, Colorado Department of Transportation, City of Aurora, Town of Eagle, Town of Gypsum, Town of Minturn, Town of Vail, Vail Resorts, Colorado Springs Utilities, Denver Water, and the U.S. Department of Agriculture Forest Service (FS), compiled macroinvertebrate (73 sites, 124 samples) data previously collected in the Eagle River watershed from selected USGS and FS studies, 2000–07. These data were analyzed to assess the biological condition (that is, biologically “degraded” or “good”) at selected sites in the Eagle River watershed and determine if site class (for example, urban or undeveloped) described biological condition.

An independently developed predictive model was applied to calculate a site-specific measure of taxonomic completeness for macroinvertebrate communities, where taxonomic completeness was expressed as the ratio of observed (O) taxa to those expected (E) to occur at each site. Macroinvertebrate communities were considered degraded at sites were O/E values were less than 0.80, indicating that at least 20 percent of expected taxa were not observed. Sites were classified into one of four classes (undeveloped, adjacent road or highway or both, mixed, urban) using a combination of riparian land-cover characteristics, examination of topographic maps and aerial imagery, screening for exceedances in water-quality standards, and best professional judgment. Analysis of variance was used to determine if site class accounted for variability in mean macroinvertebrate O/E values. Finally, macroinvertebrate taxa observed more or less frequently than expected at urban sites were identified.

This study represents the first standardized assessment of biological condition of selected sites distributed across the Eagle River watershed. Of the 73 sites evaluated, just over half (55 percent) were considered in good biological condition (O/E greater than 0.80). The remaining sites were either consistently biologically degraded (30 percent; O/E less than 0.80) or varied annually between good and degraded condition (15 percent; O/E is less than or greater than 0.80). Sites primarily affected by urbanization were among the most severely degraded (lowest O/E values) when compared to other site classes. Although most urban sites were among the most severely degraded (lowest O/E values), a few sites had nearly intact macroinvertebrate communities (O/E near 1.0). Similar observations were noted among sites classified as mixed. Thirteen macroinvertebrate taxa were identified that occurred more or less frequently than expected at urban sites. Additionally, six other taxa were impartial (tolerant) to the same conditions. Combined, these 19 taxa provide an opportunity to enhance the interpretation of future studies in the Eagle River watershed, but will require better insight into the responses of these taxa to specific stressors. Understanding the sources of variability affecting biological condition along with why some sites expected to be degraded, but showed otherwise, will have clear implications for mitigation efforts. Integrating results of this study with field and laboratory investigations will greatly enhance the ability to identify causal factors affecting biological condition at degraded sites, the logical next step. Information generated from such integrative studies will be imperative for well targeted mitigation efforts in the Eagle River watershed.

First posted September 7, 2010

For additional information contact:

Director, USGS Colorado Water Science Center
Box 25046, Mail Stop 415
Denver, CO 80225

http://co.water.usgs.gov

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Suggested citation:

Zuellig, R.E., Bruce, J.F., Healy, B.D., Williams, C.A., 2010, Macroinvertebrate-based assessment of biological condition at selected sites in the Eagle River watershed, Colorado, 2000–07: U.S. Geological Survey Scientific Investigations Report 2010–5148, 19 p.



Contents

Abstract

Introduction

Purpose and Scope

Study Area

Study Methods

Data Collection

Macroinvertebrate Sampling

Macroinvertebrate Data Preparation and Comparability

Assigning Site Classes

Data Analysis

Macroinvertebrate Predictive Model

Predictive Model Description and Performance

Applying the Predictive Model to the Eagle River Watershed Dataset

Assessing Biological Condition

Comparing Biological Condition Among Site Classes

Annual Variability in Observed/Expected

Observed and Expected Macroinvertebrate Taxa Occurrences at Urban Sites

Macroinvertebrate-Based Assessment of Biological Condition

Site Class and Biological Condition

Annual Variability of Observed/Expected

Observed and Expected Macroinvertebrate Taxa at Urban Sites

Summary and Conclusions

Acknowledgments

References Cited


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