During the first year of the proj ect (Weissman et al. 1988), all experimental work was carried out using the small ponds, which allowed essentially fully automatic operation and continuous dilution, as well as heating if needed. The objectives were to determine long-term productivity and stability for this site with previously studied and new species. Five of the strains inoculated into the 3-m2 ponds were successfully cultivated, including two that derived from local isolates (one of which had invaded these ponds). Three of the culture collection strains could not be cultivated stably in the small ponds. Reproducibility of the experiments was tested, with the conclusion that differences between the different treatments should be judged significant only if these approached 20%.

Productivities in the summer month of August reached 3 0 g/m2/d for C. cryptica CYCLO1, but decreased to about half this level in September and October. At this point, M. minutum (MONOR2) was used, as this is a more cold-tolerant organism. By November productivity of MONOR2 fell to about 10 g/m2/d, and was very low (3.5 g/m2/d) in December in unheated ponds. Remarkably, despite these ponds freezing over repeatedly, the culture survived and exhibited some productivity. During August and September, productivities for CYCLO1 and Amphora sp. exhibited short-term excursions above 40 g/m2/d. Faulty data are not suspected.

A physical model of the pond environment developed by David Tillett at the Georgia Institute of Technology, combining climatic, design, operation, physico-chemical and biological process characteristics, was validated with temperature data from ponds in Roswell (see Section III. B.6).

The large-scale system was completed by the second year. Some problems were encountered: the spongy clay at the site did not compact well, resulting in an uneven pond bottom. This made it difficult to clean and drain the ponds, and resulted in settling and sedimentation of solids. Significant differences were noted between the lined (north) and unlined (south) ponds, in terms of mixing velocities, head losses, and roughness coefficients. In any case, power inputs at low mixing velocities (<30 cm/s) were relatively low (<0.1 w/m2). The efficiency of CO2 injection into the ponds through the carbonation sumps (at approximately 0.6 to 0.9-m depth) was estimated at close to 90%. From the measured gas transfer coefficient, outgassing losses from the lined pond were estimated as approximately 10% depending on pH levels. Also, the unlined pond lost 0.3-0.4 cm/d more water due to percolation.