During an intensive water-quality study of the Sacramento River at Bend Bridge, Calif., from September 4 to 7, 1973, differences in selected water-quality constituent concentrations were evaluated at three locations at a single site in the river for two 24-hour periods. Water temperature, dissolved oxygen, pH, specific conductance, selected major ions and plant nutrients, and phytoplankton were measured and analyzed to determine thoroughness of mixing in the transection.
Slight fluctuations in constituent concentrations occurred with time although the vertical and horizontal differences among sampling locations were not statistically significant at the 0.05 probability level. Consequently, one location probably would have been sufficient to obtain representative concentrations of most water-quality constituents at this site. The measured concentration differences, especially in the plant nutrients, may be of some biological importance where slight fluctuations in low concentrations may cause limiting conditions for plant growth. Phytoplankton concentrations were so erratic with time that if only one sample were collected, any collection time during a diel period would be as valid as any other.
