USE OF IN SITU MICROCOSMS FOR EVALUATING RESERVOIR WATER MANAGEMENT OPTIONS¹

Abstract

The use of in situ microcosms for performing reservoir trophic studies and aiding in the design of reservoir restoration programs are discussed. The site of this study was Lahontan Reservoir, Nevada, which has experienced water quality problems associated with monospecific blooms of blue‐green algae and hypolimnetic dissolved oxygen depletions. In situ microcosms were used to investigate the response of phytoplankton species composition to additions of the nutrients nitrogen, phosphorus, and the phosphorus precipitant aluminum sulfate. At the end of the 16‐day experimental period, the microcosms receiving the phosphate treatments yielded the highest standing crops of algae and the greatest percentage composition of blue‐green algae. The microcosms receiving the nitrate treatment exhibited greater initial algal concentrations followed by a decline in photoplankton, which coincided with an increase in the zoo‐plankton population. The results presented here suggest that microcosms can be a cost‐effective method for assessing reservoir water quality and planning restoration programs.