In the time frame between the end of the California projects and before initiation of the Roswell project, John R. Benemann and Dr. David Tillett carried out a research project in support of these outdoor pond projects (Benemann and Tillett 1987, 1990). This project included studies of the effect of nutrient limitations, specifically N and Si, on lipid induction, the effects of fluctuating conditions (temperatures, O2, light) on culture dominance and productivity, and the development of a mathematical model of the algal pond environment. That “Algal Pond Model,” (APM) could be used in designing experimental protocols and predicting culture performance.

A basic premise of this project was that the algal pond environment experienced by microalgal cells is characterized by relatively consistent and predictable fluctuations in a rather limited set of variables, specifically light intensity, temperature, pH/pCO2, and pO2. The first two are essentially uncontrolled, although somewhat predictable, variables. The second two factors are consequences of light and temperature, as well as the pond chemistry and hydraulics (outgassing), and algal productivity. Further, it was argued that some of these variables, such as the last three, could be well modeled, based on mass and heat balances and algal growth models. One uncertainty is whether short-term (<0.1 h) light fluctuations caused by pond mixing, can be averaged over the time scales of interest (>1 h). With this assumption it would be possible to predict, and reproduce on a small-scale, the key environmental parameters of outdoor ponds to which microalgae likely would respond, determining productivity and culture stability.

Such “down-scaling” of parameters, as summarized in Table III. B.4., would allow more realistic modeling at the laboratory, or very small outdoor scale, of the conditions encountered by microalgae in large-scale ponds. And it would allow, in turn, more controlled and easily interpretable experiments on species productivity and even dominance. As one of its objectives, and in collaboration with the prior studies (Section III. B.5.; Weissman and Tillett 1989, 1992), this project resulted in the development of an APM. Many experiments were also conducted on species growth responses and competition under fluctuating environmental conditions. Finally, lipid productivity was investigated under conditions of nutrient limitation.