TABLE 5.
Summary Statistics of Yields and Source Shares From Incremental Catchments in the United States Pacific Northwest (2002 conditions)
| Total Nitrogen | Total Phosphorus | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Percentiles | Percentiles | |||||||||||||
| Mean | SD | 10th | 25th | 50th | 75th | 90th | Mean | SD | 10th | 25th | 50th | 75th | 90th | |
| Incremental yield (kg/km2/year) | 475 | 5,910 | 17.5 | 53.9 | 121 | 301 | 846 | 72.2 | 188 | 5.82 | 8.60 | 15.7 | 39.1 | 76.80 |
| Source shares (%) | ||||||||||||||
| Point sources | 1.0 | 8.3 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 3.9 | 10.6 | 0.0 | 0.0 | 0.1 | 0.0 | 0.0 |
| Developed land | 6.0 | 14.4 | 0.0 | 0.0 | 0.1 | 4.4 | 17.4 | 1.0 | 8.7 | 0.0 | 0.0 | 0.0 | 2.5 | 10.9 |
| Primarily Canadian drainages | 0.2 | 4.4 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.2 | 4.2 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Forest land (east) | 33.4 | 37.3 | 0.0 | 0.0 | 8.1 | 75.5 | 87.5 | - | - | - | - | - | - | - |
| Forest land (west) | 12.2 | 24.8 | 0.0 | 0.0 | 0.0 | 6.3 | 54.5 | - | - | - | - | - | - | - |
| Farm fertilizer | 8.3 | 17.0 | 0.0 | 0.0 | 0.1 | 6.3 | 32.5 | - | - | - | - | - | - | - |
| Livestock manure | 18.4 | 22.5 | 0.1 | 1.4 | 8.6 | 27.9 | 53.7 | - | - | - | - | - | - | - |
| Farm fertilizer and livestockmanure | - | - | - | - | - | - | - | 10.7 | 16.7 | 0.1 | 0.5 | 3.0 | 12.2 | 36.2 |
| Geologic material | - | - | - | - | - | - | - | 84.2 | 22.2 | 47.8 | 80.0 | 94.6 | 99.1 | 99.9 |
| Atmospheric deposition | 14.4 | 17.9 | 3.0 | 5.6 | 9.7 | 14.0 | 26.7 | - | - | - | - | - | - | |
| Red alder trees | 6.3 | 15.2 | 0.0 | 0.0 | 0.0 | 0.5 | 28.7 | - | - | - | - | - | - | |
Notes: SD, standard deviation; -, not applicable.
Incremental yields represent the load generated within an incremental watershed (the area that drains directly to a stream reach without passing through another stream reach) divided by the area of the incremental watershed. Incremental yield accounts for the effects of instream aquatic loss associated with one-half the reach time of travel (if applicable). Source shares represent the contribution from each source as a percentage of the incremental yield.