IMPACTS OF A DESERT IMPOUNDMENT ON THE PHYTOPLANKTON COMMUNITY OF THE LOWER COLORADO RIVER.

The paper discusses possible impacts of Glen Canyon Dam on the downstream phytoplankton community of the Colorado River. The Colorado River supports a relatively small phytoplankton population dominated by tychoplankters. Chemically, the river is satisfactory for euplanktonic development; however, the inability of the river to support a euplanktonic community is likely the result of physical factors that can be largely attributed to upstream impoundment. The low temperature discharge from Lake Powell limits phytoplankton growth and development. Frequent and large changes in discharge from Glen Canyon Dam result in widely fluctuating river levels. As a consequence, populations of primarily tychoplanktonic forms increase or decrease in the river. Other physical factors which may preclude appreciable phytoplankton development in the Colorado River are the limited age of the water and turbidity.