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. 2011 Oct;47(5):1110–1135. doi: 10.1111/j.1752-1688.2011.00580.x

TABLE 4.

Model Statistics for the Total Nitrogen and Total Phosphorus SPARROW Models Developed for the United States Pacific Northwest

90% Confidence Interval for the Model Coefficient
Parameter Model Coefficient Units Model Coefficient Lower Upper Standard Error of the Model Coefficient Probability Level (p-value) Nonparametric Bootstrap Estimate of Coefficient (mean)
Total Nitrogen
Sources
Primarily Canadian drainages1 (km2) kg/km2/year 120 19 220 61 0.0256 107
Atmospheric deposition2 (kg/year) Dimensionless 0.10 0.00 0.23 0.08 0.1050 0.11
Point sources3 (kg/year) Dimensionless 1.60 0.24 2.96 0.82 0.0268 1.59
Farm fertilizer4 (kg/year) Dimensionless 0.048 0.015 0.081 0.020 0.0080 0.047
Livestock manure5 (kg/year) Dimensionless 0.113 0.034 0.192 0.048 0.0098 0.122
Developed land6 (km2) kg/km2/year 941 495 1,387 270 0.0003 938
Forest land (west)7 (km2) kg/km2/year 78 27 129 31 0.0060 79
Forest land (east)8 (km2) kg/km2/year 115 73 156 25 <0.0001 113
Red alder trees9 (m2) kg/m2/year 0.31 0.00 0.64 0.20 0.0597 0.31
Land-to-water delivery
Effective precipitation10 (cm) cm−1 1.07 0.69 1.46 0.23 <0.0001 1.46
Hydrologic landscape region 2011 (%) Dimensionless −1.19 −1.82 −0.57 0.38 0.0020 −0.57
Aquatic loss
Instream - - - - - - -
Reservoir - - - - - - -
Model diagnostics
MSE 0.410 R2 load 0.892
RMSE 0.640 R2 yield 0.759
Number of observations 178
Total Phosphorus
Sources
Primarily Canadian drainages1 (km2) kg/km2/year 3.80 −0.39 7.99 2.54 0.0679 0.09
Geologic material12 (ppm·km2) Dimensionless 0.0155 0.0115 0.0194 0.0024 <0.0001 0.0151
Point sources3 (kg/year) Dimensionless 1.03 0.21 1.86 0.50 0.0195 1.05
Farm fertilizer4 and livestock manure5 (kg/year) Dimensionless 0.018 0.005 0.032 0.008 0.0122 0.017
Developed land6 (km2) kg/km2/year 61.7 22.7 100.7 23.6 0.0048 53.0
Land-to-water delivery
Effective precipitation10 (cm) cm−1 1.41 1.15 1.66 0.15 <0.0001 1.42
Permeability13 (cm/hour) hour/cm −0.33 −0.49 −0.17 0.10 0.0008 −0.32
Hydrologic landscape region 2011 (%) Dimensionless −0.68 −1.13 −0.24 0.27 0.0122 −0.64
Aquatic loss
Instream14 day−1 0.093 0.007 0.180 0.052 0.0383 0.083
Reservoir - - - - - -
Model diagnostics
MSE 0.480 R2 load 0.858
RMSE 0.693 R2 yield 0.712
Number of observations 228

Notes: SPARROW, SPAtially Referenced Regressions On Watershed attributes; MSE, mean squared error; RMSE, root mean squared error; -, not applicable.

1

Drainage area for watersheds with more than 50% located in Canada.

2

Annual wet deposition of inorganic nitrogen (ammonia and nitrate), 2002.

3

Surface-water discharges from permitted wastewater discharge, 2002.

4

Commercial fertilizer applied to agricultural land, 2002.

5

Manure produced by livestock animals, 2002.

6

Area of developed land, 2001.

7

Area of forest land, west side of Cascade Range, 2001.

8

Area of forest land, east side of Cascade Range, 2001.

9

Basal area of red alder trees, 2001.

10

Natural log of effective mean annual precipitation (local precipitation plus the depth of irrigation water).

11

Percentage of land that is hydrologic landscape region 20 (humid mountains with permeable soil and impermeable bedrock).

12

Phosphorus content of geologic material, mass ppm scaled by catchment area.

13

Natural log of mean soil permeability.

14

Phosphorus loss in stream with mean annual streamflow <13.4 m3/s.

The p-values for the source variables are based on a one-sided t-test; the p-values for the land-to-water delivery variables are based on a two-sided t-test.