Table 4. Model statistics for the total phosphorus National Hydography SPARROW model developed for the United States Pacific Northwest.


[The p-values for the source and aquatic loss 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. Abbreviations: NHD, National Hydrography Dataset; NLLS, non-linear least squares; RMSE, root mean squared error; R², coefficient of determination; cm, centimeter; kg/km²-yr, kilogram per square kilometer per year; kg/yr, kilogram per year; km²; square kilometer; mm, millimeter; <, less than; –, not applicable]


Parameter	Model coefficient units	NLLS estimate of model coefficient	Standard error of the model coefficient	Probability level (p-value)	90 percent confidence interval for the model coefficient		Nonparametric bootstrap estimate of model coefficient
					Lower	Upper
Sources
Forestland (west)1 (km2)	kg/km2-yr	9.23	2.87	0.0015	5.47	14.08	10.15
Forestland (east)2 (km2)	kg/km2-yr	6.81	1.42	< 0.0001	4.29	12.24	8.43
Scrub and grass land3 (km2)	kg/km2-yr	0.54	0.32	0.0898	-10.66	0.77	-3.28
Point sources4 (kg/yr)	dimensionless	1.20	0.33	0.0003	0.63	1.55	1.17
Developed land5 (km2)	kg/km2-yr	24.3	5.5	< 0.0001	19.7	29.9	24.6
Farm fertilizer6 (kg/yr)	dimensionless	0.015	0.007	0.0271	0.002	0.025	0.014
Confined cattle7 (kg/yr)	dimensionless	0.035	0.014	0.0100	0.019	0.060	0.038
Grazing livestock8 (kg/yr	dimensionless	0.124	0.022	< 0.0001	0.094	0.195	0.143
Springs and power returns9 (kg/yr)	dimensionless	1.67	1.13	0.1408	1.17	2.53	1.76
Land-to-water delivery
Precipitation10 (mm)	–	1.26	0.17	< 0.0001	0.86	1.52	1.20
Base flow index11 (percent)	–	-0.012	0.006	0.0340	-0.024	-0.001	-0.012
Aquatic loss
Free-flowing streams	–	–	–	–	–	–	–
Impoundments	–	–	–	–	–	–	–
Model diagnostics
R2 of yield	–	0.810	–	–	–	–	–
RMSE	–	0.549	–	–	–	–	–
Number of observations	–	220	–	–	–	–	–

¹ Area of forest land, west side of Cascade Range, 2001.


² Area of forest land, east side of Cascade Range, 2001.


³ Area of scrub and grass land, 2001. 


⁴ Surface-water discharges from permitted wastewater facilities, 2002.


⁵ Area of developed land, 2001.


⁶ Commercial fertilizer applied to agricultural land, 2002.


⁷ Manure from cattle in dairies and feedlots, 2002.


⁸ Manure from grazing livestock, 2002.


⁹ Surface-water discharge from springs and power returns, 2002.


¹⁰Natural log of mean annual precipitation, 1971–2000.


¹¹Mean percentage of streamflow due to base flow.

First posted July 17, 2013