TABLE 9.
Summary of Point-Source Total Nitrogen Input to Selected Six-Digit Hydrologic Unit Code (HUC6) Watersheds in the United States Pacific Northwest (2002 conditions)
| Contribution to Total Nitrogen Point-Source Loading (%) | ||||||
|---|---|---|---|---|---|---|
| Six-Digit Hydrologic Unit Code Watershed | Point-Source Contribution to Discharged Total Nitrogen Load (%) | Sewage Treatment Facilities | Animal Aquaculture and Fish Hatcheries | Pulp and Paper Mills | Food Processing | Other |
| Spokane River (170103) | 42.0 | 99.0 | 0.0 | 1.0 | 0.0 | 0.0 |
| Upper Snake River (170402) | 38.7 | 35.1 | 52.2 | 0.0 | 12.7 | 0.0 |
| Middle Snake-Boise Rivers (170501) | 30.4 | 53.4 | 35.6 | 0.0 | 10.9 | 0.0 |
| Middle Snake-Powder Rivers (170502) | 28.2 | 54.3 | 35.0 | 0.0 | 10.8 | 0.0 |
| Lower Snake River (170601) | 20.9 | 55.0 | 31.8 | 3.5 | 9.8 | 0.0 |
| Upper Columbia River (170200) | 20.0 | 68.0 | 21.7 | 3.5 | 6.7 | 0.1 |
| Willamette River (170900) | 30.1 | 96.8 | 0.0 | 3.1 | 0.0 | 0.1 |
| Lower Columbia River (170800) | 26.3 | 83.0 | 7.4 | 5.6 | 2.3 | 1.7 |
| Puget Sound (171100) | 37.4 | 95.7 | 0.2 | 3.4 | 0.0 | 0.6 |
Notes: Values indicate the percentage of the total point-source loading from each category, and reflect the total upstream area draining to the outlet of each watershed. Results are only shown for watersheds where point sources contributed at least 20% of the total nitrogen load discharged from the watershed.