Dissolved Oxygen Regimen Of The Willamette River Oregon Under Conditions Of Basinwide Secondary Treatment

What is involved in restoring a river? River Quality: Dynamics and Restoration answers this question through a series of articles and case studies written by some of the field's leading researchers and practitioners. The first part of the book covers the physical, chemical, and biological dynamics of a river system. The second part describes monitoring programs and remedial measures used to restore river systems back to healthy and functional states. The Willamette River in Oregon and the Vistula River in Poland are used to illustrate the dynamic and restoration processes. Each river is in a different stage of restoration and is subjected to different degrees of stress from agriculture, industry, and urbanization. The Willamette is an internationally cited example of a restored river, while the Vistula is a river that has just recently begun the restoration process. Contrasts and comparisons of the two river systems enable readers to learn the limitations of restoration processes and what is involved in the different stages of restoration.

For nearly half a century the Willamette River in Oregon experienced severe dissolved-oxygen problems related to large loads of organically rich waste waters from industries and municipalities. Since the mid-1950's dissolved oxygen quality has gradually improved owing to low-flow augmentation, the achievement of basinwide secondary treatment, and the use of other waste-management practices. As a result, summer dissolved-oxygen levels have increased, salmon runs have returned, and the overall effort is widely regarded as a singular water-quality success. To document the improved dissolved-oxygen regimen, the U.S. Geological Survey conducted intensive studies of the Willamette during the summer low-flow seasons of 1973 and 1974. During each summer the mean daily dissolved-oxygen levels were found to be higher than 5 milligrams per liter throughout the river. Because of the basinwide secondary treatment, carbonaceous deoxygenation rates were low. In addition, almost half of the biochemical oxygen demand entering the Willamette was from diffuse (nonpoint) sources rather than outfalls. These results indicated that point-source biochemical oxygen demand was no longer the primary cause of dissolved-oxygen depletion. Instead, the major causes of deoxygenation were nitrification in a shallow ' surface active ' reach below Salem and an anomalous oxygen demand (believed to be primarily of benthal origin) in Portland Harbor.