Clinch and Powell Valley Watershed Ecological Risk Assessment
The free-flowing Clinch and Powell Valley watershed, which drains into Norris Lake in northeastern Tennessee, has historically had one of the richest assemblages of native fish and freshwater mussels in the world. Nearly half of the species historically present are now extinct, threatened, or endangered. The U.S. Environmental Protection Agency's ecological risk assessment framework was used to structure a watershed-scale analysis of associations between land use and in-stream habitat and their effects on fish and mussels.
A pilot study of one of four subwatersheds determined that the fish Index of Biotic Integrity (IBI) was a useful surrogate for mussel species richness and found the optimal spatial scale to describe associations between land use, stressors, and biota. These findings were used to structure the watershed risk analysis of relationships between sources, stressors, and effects.
Percent pasture area, percent crop land, and proximity to active mining, urban areas, or major transportation routes accounted for more than half of the variance in fish IBI scores, with coal mining having the most impact. Native fish and mussel populations appeared to be at greatest risk as more stressors co-occurred. Our results indicate that a number of sources and stressors are responsible for the decline in native species in the Clinch and Powell Valley watershed, but naturally vegetated riparian corridors may help mitigate some of these effects.