The marine phytoplankter Tetraselmis suecica was grown in shallow outdoor flumes for a period of approximately 6 months at the Natural Energy Laboratory of Hawaii. In full sunlight, gross production rates were 15-20 g C m(-2) d(-1). The corresponding photosynthetic efficiencies (PE's) were 9-10%. Respiration losses removed about half the gross production. The CO(2) utilization efficiencies of 96 +/- 11% were achieved by bubbling CO(2) into the culture with the use of a counterflow sump system. Adding the CO(2) in the form of carbonated water resulted in utilization efficiencies of 81 +/- 11%. Archimedes screws proved superior to both paddle wheels and propellers as a means of circulating the water in the flumes. Insertion of foil arrays into the flumes to effect systematic mixing of the culture significantly enhanced production. The enhancement was greater when the foils were oriented at a small angle relative to the horizontal than when they were oriented at the same angle relative to the vertical. Light modulation effects are implicated as the probable cause of most of the enhancement. Substitution of electric power plant stack gases for pure CO(2) resulted in no significant change in the production of T. suecica grown in chemostat culture.

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