Assessment of Macroinvertebrates Communities of the Tualatin River Basin, November 2000

Aquatic life in the Tualatin River Basin has likely undergone substantial change as human influence has altered water quality, physical habitat, and hydrology for more than 100 years. The objective of this study was to determine the condition of macroinvertebrate communities in tributaries to the Tualatin River. Macroinvertebrate communities were sampled from 44 sites on 22 tributaries of the Tualatin River. A modified multimetric index was used to determine the condition of the macroinvertebrate community at each study site. 

The condition of macroinvertebrate communities varied widely among stream reaches in the basin. A number of rural streams in forested areas (upper Chicken Creek, upper Dairy Creek, and Roaring Creek) had diverse communities well represented by mayflies, stoneflies, caddisflies, and other more sensitive species. These reaches were used as reference sites against which other sites were compared. Urban streams generally showed the highest levels of impairment relative to reference conditions. Mayflies, stoneflies, caddisflies, and other sensitive taxa generally were absent from the most impaired urban reaches. 

This study provides the first comprehensive set of data describing macroinvertebrate communities in the Tualatin River Basin. The data can help prioritize future restoration efforts and serve as baseline information to help assess further degradation or future improvement of stream reach conditions.