The screening and characterization protocols used by SERI researchers were refined for the 1984 collecting season. Included in these refinements was the development of a modified “rotary screening apparatus”, a standard type of motorized culture mixing wheel for 16×150-mm culture tubes. The rotating wheel was constructed of Plexiglas to allow better light exposure (see Figure II. A.1). The wheel was typically illuminated with a high-intensity tungsten stage lamp, and

could be placed inside a box behind a CuSO4-water heat filter for temperature control. The Plexiglas wheel allowed all the cultures to receive equal illumination. Another technological advance used a temperature-salinity gradient table to characterize the thermal and salinity preferences and tolerances of the isolates.

Development of artificial saline media.

One of the most significant contributions made by SERI researchers during 1984 was the development of media that mimicked the saline water in shallow aquifers in the southwestern United States. This was an important undertaking because it allowed algal strains to be screened for growth in the types of water that would likely be available in an outdoor mass culture facility. To identify the major water types available in the southwestern United States, state and federal reports that described the chemical characteristics of water from 85 saline wells in New Mexico were studied. The data were statistically analyzed to identify the relationships between the various ionic constituents. (Data from wells deeper than 83 m was not used in this analysis, because the cost of pumping water from those depths was prohibitive.) R-mode factor analysis indicated that two factors were largely responsible for the differences between the waters examined (Barclay et al. 1988). The first factor, monovalent ion concentration, was responsible for 40% of the variance; the second factor, divalent ion concentration, for 30%. A plot of these factors against each other clearly delineated two primary water types, referred to as “Type I” and “Type II”. Type I waters were characterized by a low monovalent-to-divalent ion ratio (average value = 0.4), whereas Type II waters had a higher level of monovalent ions (monovalent-to — divalent ion ratio of 9.4). The major ions present in Type I water were Na+, Cl-, Mg2+, and Ca2+. The major ions of Type II water were Na+, Cl-, SO42-, and HCO3-. Type II water is consequently termed a “sodium bicarbonate class” of water. Approximately three-fourths of the saline well waters were of the Type II variety, and one-fourth could be characterized as Type I.

The survey indicated that both types of water exhibited a range of conductivities; the researchers believed that the higher-conductivity waters resulted from evaporation of the lower conductivity waters. In addition, they recognized that the conductivity of the water in an outdoor production pond would increase with time because of the high rates of evaporation in the southwestern United States (as high as 1 cm^day-1). Therefore, artificial media that covered a wide range of conductivities had to be developed. To this end, an experiment was conducted in which media that contained the salts typically present in low-conductivity Type I and Type II waters were allowed to evaporate with stirring at 35°C. Samples were removed at various times and filtered. The ions still dissolved in the waters were quantified using an inductively coupled plasma spectrometer and a high-performance liquid chromatograph. In this manner, media formulations were derived at SERI that covered a range of conductivities (from 10 to 70 mmho^cm-1) for both media types. The media most commonly used were designated SERI Type I/10, Type I/25, Type I/55, Type I/70, Type II/10, Type II/25, Type II/55, and Type II/70, in which the number following the slash indicates the specific conductivity of the medium. The compositions of these media are given in Figure II. A.2.

In order to assess whether these media formulations accurately reflected the types of water in desert region surface waters, samples of the water at numerous algal collection sites in the southwestern United States were chemically analyzed. The relative compositions of the anionic and cationic constituents were then plotted on separate trilinear plots, which allowed a graphical representation of the various water samples relative to SERI Type I and Type II media (Figure II. A.3). This analysis indicated that Type I water has higher proportions of Mg2+ and Ca2+ than most surface waters examined, whereas Type II water was fairly representative of the sampled waters with respect to these cations. On the other hand, natural surface waters often had an anion composition similar to both SERI Type I and Type II media. The researchers concluded that these artificial media would serve well as standardized media for testing newly acquired strains, thereby allowing all ASP researchers (both in-house personnel and subcontractors) to screen strains for growth potential in waters similar to those that would be available for commercial production.