Publication Summary

Report to Washington State Department of Ecology (Contract No. C0091223). Prepared by University of Washington Department of Civil Engineering, Technical Report No. 133, Seattle. A scoping analysis to evaluate existing and potential eutrophication problems in the upper Columbia River and Lake Roosevelt was conducted during the summer of 1991. Existing data were compiled describing physical and chemical characteristics of the river and reservoir. Additional data were collected during the summer of 1991 to further describe water quality.

Report to Washington State Department of Ecology (Contract No. C0091223). Prepared by University of Washington Department of Civil Engineering, Technical Report No. 133, Seattle. A scoping analysis to evaluate existing and potential eutrophication problems in the upper Columbia River and Lake Roosevelt was conducted during the summer of 1991. Existing data were compiled describing physical and chemical characteristics of the river and reservoir. Additional data were collected during the summer of 1991 to further describe water quality. Trophic state indicators such as reservoir nutrient concentrations, phytoplankton, transparency, and periphyton were evaluated. Critical nutrient loading criteria were developed to the extent possible using available data supplemented with collections during the study.

Phytoplankton growth was found to be limited by nitrogen, light, and to some extent, flushing. Cladophora, a notorious nuisance periphytic green alga, occurs in nuisance proportions in Lake Roosevelt. A periphyton model showed that reductions in phosphorus loading by one-half could possibly reduce Cladophora biomass below a perceived nuisance level. A recommendation to reduce phosphorus loading to achieve target Cladophora biomass was not made because of tentative model calibration data. A thorough monitoring of periphyton biomass at about 10 stations throughout the length of the reservoir was recommended to calibrate an appropriate model. More complete seasonal and longitudinal data on nutrients and phytoplankton were also considered to be necessary.