Investigations into the Microbial Ecology and Limnology of Hyrum Reservoir, in Northern Utah

A series of preliminary investigations was carried out to determine the factors promoting the dense, late summer waterblooms of Aphanizomenon flos-aguae in Hyrum Reservoir in northern Utah. Attempts were made to culture the Aphanizomenon in the ASM-8a medium of O'Flaherty and Phinney (J. Phycol. 6:95-97. 1970), but no growth was obtained and the algae soon lysed. Cultures were maintained, without growth, for more than four months in a lake water--lake sediment medium at 17 C under 1500 lux flourescent light. Dissolved oxygen measurements using an in situ probe revealed the development of a sharp oxycline during the summer months; on one day the dissolved oxygen concentration was observed to drop from 118% saturation (8.6 mg O2/1) at 6.5 meters depth, to 33% saturation (2.4 mg O2/l) at 7 meters, with a concurrent temperature decrease from 21.5 C to 21 C. During the same period, pH was found to drop from 8.6 at the surface to 8.5 at 5 meters, 8.0 at 10 meters, and to 7.8 at the bottom (16 meters). Secchi disc depth corresponded to 14% of the incident radiation, this depth varying from l.3 to l.8 meters during the algal bloom. The photic zone (1% of incident radiation) extended to 3.5 meters depth. Water samples were collected from late April until early October, and these were analyzed for total organic carbon (TOC) using a Beckman model 915 total organic carbon analyzer. The organic carbon concentrations were found not to vary significantly with season or location. Many of the samples contained large numbers of Aphanizomenon but carbon analyses did not reflect this. It was concluded that the phytoplankton carbon in the reservoir was so much smaller than the carbon in the form of other organic materials, such as microseston, bacteria, detritus, colloids, and dissolved material, that fluctuations in algal carbon were therefore masked by the large amount of carbon continually present in these other forms. The mean organic carbon concentration for the lake was 4.6 mg/1 (n=118, s=1.47) and the range was from 1.2 to ...