An Assessment of the Chemical, Habitat and Biological Condition of Wadeable Streams Habitat of the Oregon Coastal Coho Salmon

Aaron N. Borisenko and Michael P. Mulvey

Oregon Department of Environmental Quality, Watershed Assessment Section, Portland, Oregon

We conducted a six-year study of the biological, chemical and habitat quality of first through third order, wadeable Coho salmon habitat streams in the Oregon Coastal Coho Evolutionarily Significant Unit (ESU). Oregon Coastal Coho are listed as threatened under the Endangered Species Act. We surveyed 129 randomly selected streams and 29 reference streams between 1998 and 2003 during June, July, August and September using the US EPA Environmental Monitoring and Assessment Program (EMAP) wadeable streams protocol.

We found that the most extensive stressors were warm water temperatures, high levels of total solids, high phosphorus and high levels of fine sediment. These stressors impair approximately 40 to 50% of Coho habitat wadeable stream miles. Although low dissolved oxygen, non-native vertebrate species and pH standard violations were not extensive (<10% of stream miles), these stressors were a highly significant risk factor to the biological integrity of aquatic vertebrates and macroinvertebrates when present. Relative to high quality reference sites, Coho habitat streams tended to have higher fine sediment, higher phosphorus, and lower dissolved oxygen. Streams on publicly owned state and federal forests tended to be in the best condition while streams in agricultural areas were in the worst condition. Streams in privately owned forested areas were of intermediate condition.

We also compared our findings to the 2002 303d List of Water Quality Limited Streams which was compiled using non-randomly selected data. Overall, the 303d List greatly underestimated both the extent and the types of impairment present relative to the probabilistic stream assessment data.

Keywords: regional stream condition assessment, threatened species, Coho salmon