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Ecological Condition of Streams in the Western Cascades Ecoregion of Oregon and Washington

Gretchen A. Hayslip 1 and Lillian Herger 1

1 U.S. Environmental Protection Agency (USEPA), Region 10, Seattle, Washington

EPA's Environmental Monitoring and Assessment Program (EMAP) is designed to monitor and assess the condition of the nation's aquatic resources. The Western Cascades ecoregion Regional EMAP project was a cooperative effort between EPA Region 10, EPA ORD, Washington Department of Ecology (Ecology) and Oregon Department of Environmental Quality (ODEQ). The purposes of this study were to describe the ecoregion streams and to determine overall stream condition based on comparisons to water quality criteria and reference condition.

This ecoregion has a moist temperate climate with elevation ranging from 2,000 to 7,000 feet. The predominant landcover is forest and timber production is the primary land use. Study sites were selected from mapped 2nd and 3rd order streams using EMAP's probabilistic design. In 1999-2000, Ecology and ODEQ sampled 79 sites. In addition, 23 sites representing reference condition were sampled. All sites were sampled using EMAP surface waters protocols.

Water column indicators were compared to applicable State water quality criteria and physical habitat and biological assemblages indicators were compared to the reference condition calculated from the reference sites. The 5th and 25th percentiles of this reference distribution were used to designate 'good', 'fair', and 'poor' categories.

Few (3-8%) of the stream miles were in "poor" condition based on water column indicators. Physical habitat indicators showed more stream miles in "poor" condition (27-46%). The biota are likely responding to alterations in physical habitat, as 14-32 % of the stream miles were in "poor" condition using biological indicators (fish, amphibians, and macroinvertebrates).

Keywords: EMAP, streams, physical habitat, fish, amphibians, macroinvertebrates, Washington, Oregon

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