Smith,S.V., Swaney,D.P., Buddemeier,R.W., Scarsbrook,M.R., Weatherhead,M.A., Humborg,C., Eriksson,H. and Hannerz,F.(2005): River nutrient loads and catchment size. Biogeochemistry, 75, 83-107.

『河川の栄養負荷と流域の大きさ』

『Abstract
　We have used a total of 496 samples sites to calibrate a simple regression model for calculating dissolved inorganic nutrient fluxes via runoff to the ocean. The regression uses the logarithms of runoff and human population as the independent variables and estimates the logarithms of dissolved inorganic nitrogen and phosphorus loading with R 2 values near 0.8. This predictive capability is about the same as has been derived for total nutrient loading with process-based models requiring more detailed information on independent variables. We conclude that population and runoff are robust proxies for the more detailed application, landscape modification, and in-stream processing estimated by more process-based models. The regression model has then been applied to a demonstration data set of 1353 river catchments draining to the sea from the North American continent south of the Canadian border. The geographic extents of these basins were extracted from a 1-km digital elevation model for North America, and both runoff and population were estimated for each basin. Most of the basins (72％ of the total) are smaller than 103 km2, and both runoff and population density are higher and more variable among small basins than among larger ones. While total load to the ocean can probably be adequately estimated from large systems only, analysis of the geographic distribution of nutrient loading requires consideration of the small basins, which can exhibit significant hydrologic and demographic heterogeneity between systems over their range even within the same geographic region. High-resolution regional and local analysis is necessary for environmental assessment and management.

Key words: inorganic nutrient loading; population; runoff; catchment size; North America』

Abbreviations
Introduction
Objectives
Materials and methods
　Nutrient flux analysis
　　Data used
　　Regression analysis and comparison data
　Analysis of spatial distribution of nutrient fluxes to the sea
Results
　Basin sizes
　Basin load regression equations
　Demonstration basins
Discussion
　Global analysis: estimated basin nitrogen loads
　Basin size: effects and implications
　Application and tests: the North America demonstration data
Summary and conclusions
References

Table 1. Data sets used for nutrient loading analyses.

Data set

Number of basins

Data Source
Meybeck 28 Meybeck (1982); see also Smith et al. (2003)
LOICZ 136 Smith et al. (2003)
NAWQA 175 http://water.usgs.gov/nawqa/nutrients/datasets/nutconc2000/
NRWQN 77 Smith and Maasdam (1994) and Maasdam and Smith (1994)
BED 80 http://data.ecology.su.se/models/bed.htm

Table 2. Regression analyses of N and P loading and yield.

Source

log N (mol/year)

R 2

log P (mol/year)

R 2
Loading equations
Smith et al. (2003)

-0.20 + 0.69 x log(run) + 0.32 x log(pers)
 0.81

-1.15 + 0.66 x log(run) + 0.30 x log(pers)

0.78
This paper

0.57 + 0.61 x log(run) + 0.33 x log(pers)
 0.76

-1.60 + 0.67 x log(run) + 0.34 x log(pers)

0.78
SPARROW
(Smith et al. 1997)		 　

0.87
 　

0.81

　

log N (mol/year)

R 2

log P (mol/year)

R 2
Yield equations
Smith et al. (2003) 3.99+0.75xlog(run/km2)+0.35xlog(pers/km2) 0.59 2.72+0.78xlog(run/km2)+0.36xlog(pers/km2) 0.58
This paper 4.03+0.69xlog(run/km2)+0.36xlog(pers/km2) 0.44 2.43+0.63xlog(run/km2)+0.33xlog(pers/km2) 0.38
In the cases of the results of Smith et al.(2003) and this paper, loading and regression are for dissolved inorganic N and P (DIN, DIP). For SPARROW, total N and P (TN, TP) loads are calculated. Correlations only are presented here for the SPARROW model loading estimates. (run = runoff (m3/year); pers = number of persons).

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