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Estimation of background loadings and concentrations of phosphorus for lakes in the Puget Sound region, Washington

Open-File Report 80-328

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Abstract

For lakes in watersheds that include developed land, evaluation of eutrophication is facilitated by knowledge of changes in the lakes ' phosphorus concentration since development. A method is described for estimating background phosphorus concentration in lakes of the Puget Sound lowland, Washington. Using a mass-balance ' Vollenweider-type ' model, phosphorus loadings were calculated from present-day phosphorus concentrations measured in lake water and from easily measured physical characteristics for 24 lakes in undeveloped, or insignificantly developed, watersheds. Phosphorus loading from forest (undeveloped) land was derived for each lake as the difference between the calculated phosphorus loading directly to the lake 's surface and loading by bulk precipitation (estimated from other studies). Forest-land loading to each lake was converted to the yield (mass per unit area) of the forested part of the watershed. The phosphorus yield from forest land was related to annual runoff, and the regression equation expressing this relationship explained 73% of the sample variance. By applying that regression equation to the appropriate annual-runoff data, the yield of phosphorus from forest land can be estimated for any lake in the study area. Phosphorus loading from forested land then can be added to direct loading by bulk precipitation to estimate background phosphorus loading for each lake. By applying the mass-balance model to calculated background loadings, background total-phosphorus concentration can also be calculated for all lakes in the study area that have stable thermal stratification during the summer. The standard error of estimate for calculated background loadings and concentrations averages about 25%. (USGS)

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Estimation of background loadings and concentrations of phosphorus for lakes in the Puget Sound region, Washington
Series title:
Open-File Report
Series number:
80-328
Edition:
-
Year Published:
1980
Language:
ENGLISH
Publisher:
U.S. Dept. of the Interior, Geological Survey,
Description:
iii, 40 p. ill., 1 map ;31 cm. +1 envelope.