Cell identification and sizing using digital image analysis for estimation of cell biomass in High Rate Algal Ponds

Current environmental concerns make estimation of microbial biomass a priority for monitoring purposes and to advance scientific understanding. This paper considers problems associated with algal cell imaging and measurement for cell biomass estimation in samples from high rate algal ponds. In a complex system, the only way of measuring microbial activity is to measure the individual cells and estimate biovolumes. Accurate biomass determinations demand direct microscopic counting and measurement of the sizes of individual microbial cells taken from known volumes of water. The system used for routine measurement at the laboratory where the images were generated, based on standard microscope equipment, is only suitable for treatment of well dispersed specimens. Differential interference contrast (DIC) microscopy, on the other hand, offers the best solution for optical enhancement of cell contrast, and produces an image with well defined edges, yet presents a great challenge to routine cell identification by digital image analysis, owing to the bas-relief type image produced. The paper outlines several image analysis methods developed specifically for this purpose, and presents illustrative results.