Systems and methods for delivery of gases to algal cultures

Photobioreactors according to embodiments of the present invention deliver nutrient gas intermittently to the photobioreactor media. In some embodiments, one or more gases are delivered according to a duty cycle or timing pattern. According to some embodiments, algae is grown in a photobioreactor using intermittent introduction of carbon dioxide. In other embodiments, carbon dioxide is supplied to algae grown in a photobioreactor in whole or in part from a head space above the media of the photobioreactor.