THE INFLUENCE OF LIGHT DARK CYCLES IN MIXED ALGAL CULTURES ON THEIR PRODUCTIVITY

In mass algal cultures, some form of agitation is usually provided, which amongst others, moves the organisms though an optically dense profile. During this transport, fluctuations in the light energy supply are perceived by the algae, which are of the order of 1 Hz and less. Additional to these variations the cultures are subject to diurnal, seasonal and climatic light variations. It has been suggested that turbulence with the resultant light/dark cycles enhances their productivity. However, turbulence has two major influences on an organism, i.e. it facilitates fluctuating light regimes and decreases the boundary layer which results in an increased exchange rate between the organism and its environment. With the aid of oxygen liberation measurements, the influence of fluctuating light regimes on productivity was measured. No simple relation existed, but no enhancement of productivity could be shown at cycles of 1-0.0038 Hz. Short term physiological changes were found to influence productivity severely.