PARENT SESSION
TP7 - Water Quality Criteria
Chair: Canton, Steve¹, ¹ Chadwick Ecological Consultants, Littleton, CO
2:10 PM to 5:30 PM - Tuesday, 19 November 2002
Room Ballroom A

(466) Turbidity on the Upper Willamette and Lower McKenzie Rivers from 1997 to 2001.

Thomas, Jill^*,1, Hall, Timothy¹, ¹ National Council for Air and Stream Improvement, Anacortes, WA, US

ABSTRACT- Some states have water quality standards for turbidity which are designed as an indirect approach to address concerns about adverse effects of sedimentation. These standards vary from state to state and may be expressed as an allowable percent increase (e.g. 10 to 20%) or actual NTU increase in turbidity (e.g. 5, 10 or 25 NTU) as compared to an upstream location. In Oregon there is a proposal to extend the current standard, allowing a 10% increase from non-point sources, to point sources. In light of this, an assessment was done on the background turbidity on sections of two Oregon Rivers, the upper Willamette and the lower McKenzie, and how those levels compared to current literature for thresholds of potential biological effects for salmonids and other fishes. The results from the data analysis were similar for both rivers: low background levels of turbidity (4.4 and 2.7 mean NTU for the Willamette and McKenzie, respectively), resulting in substantial percent variations between upstream reference sites (up to 68% and 63%, respectively, for same-day measurements) with 33% and 22% of the sampling dates having a greater than 10% downstream increase. The analysis also demonstrated annual downstream trends in increasing mean and range of turbidity. When the average and maximum turbidities for both rivers were compared to the current literature for threshold levels for potential biological effects, the Willamette River maximum (33 NTU), was higher than two threshold levels, cutthroat trout reduced feeding (25 NTU) and Coho salmon increased cough frequency (30 NTU). These results indicate the 10% background water quality standard will be difficult to meet for rivers with low background turbidities and is of uncertain biological relevance.

Key words: turbidity, water quality criteria, rivers, salmonids