The marine phytoplankter Pavlova lutheri was grown in both batch and continuous culture under various conditions of light and nitrate limitation in order to examine the accuracy of certain assumptions and predictions of microalgal growth models. The N : C ratio of the cells was found to be uniquely related to their relative growth rate. There was no unique relationship, however, between Chl a : C ratios and relative growth rate. Optical absorption coefficients normalized to Chl a were negatively correlated with relative growth rate at a fixed irradiance and positively correlated with irradiance at a fixed relative growth rate when light intensity was varied with neutral-density filters. Quantum yields were positively correlated with relative growth rate at a fixed irradiance and negatively correlated with irradiance at a fixed relative growth rate. Certain parameters or combinations of parameters which appear in nutrient-saturated growth models were found to be either independent of relative growth rate at a fixed irradiance or uniquely correlated with relative growth rate. This discovery facilitates extension of nutrient-saturated growth models to nutrientlimited conditions.

Arrays of foils similar in design to airplane wings have been placed in an algal culture flume to create systematic mixing. Vortices are produced in the culture due to the pressure differential created as water flows over and under the foils. In a flume having a flow rate of 30 cm/s, the foil arrays produced vortices with rotation rates of ca. 0.5-1.0 Hz. This rotation rate is satisfactory to take advantage of the flashing light effect if the culture is sufficiently dense. Solar energy conversion efficiencies in an experimental culture of P. tricornutum increased 2.2-2.4 fold with the foil arrays in place versus controls with no foil arrays and solar energy conversion efficiencies averaged 3.7% over a three-month period. Five-day running means of solar energy conversion efficiencies reached as high as 10% during the three-month period. The use of foil arrays appears to be an effective and inexpensive way to utilize the flashing light effect in a dense algal culture system.

Recent experimental evidence has made it clear that effects of irradiance and nutrient limitation on light absorption and photosynthetic quantum yields of microalgae and the relationship between cellular N : C ratios and nutrient-limited growth rates are inconsistent with the assumptions and predictions of current models of algal growth. A new algal growth model was therefore developed to overcome these inconsistencies. The new model predicts a hyperbolic relationship between nutrient-saturated growth rates and irradiance and a linear relationship between growth rate and both respiration rate and Chl a : C ratios. The correlation between growth rate and Chl a : C is positive under nutrient-limited conditions and negative under nutrient-saturated (light-limited) conditions. The requirement that N : C ratios be linearly related to relative growth rates leads to the conclusion that the product of the Chl a-specific absorption coefficient and the quantum yield coefficient be hyperbolically related to nutrient-limited growth rates, a result consistent with experimental observations. The equations relating respiration rate and compositional ratios to absolute and relative growth rates appear to be insensitive to photoperiod.

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