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Department of Biological Sciences: University of Nevada, Las Vegas


The limnetic zooplankton community of Boulder Basin, Lake Mead, was examined to determine the role of this community in the development of a metalimnetic oxygen minimum which regularly occurs in the lake. Analysis of the community from May 1975 to April 1976 revealed that zooplankton maintain high populations within the metalimnion during summer stratification. The species composition of the community changes noticeably during the summer, but due to advanced stages excysting from resting forms, a complete assemblage of individuals are found throughout the 74 day period studied. Thermal stratification was weak, covering a 30 meter metalimnion. Eddy currents powered by wind action brought oxygen into this zone from the surface, and mixing at the metalimnion-hypolimnion due to internal waves and density flows brought oxygen up into this zone. The metalimnion was sectioned into two 15 meter layers. The zooplankton consumed 33 to 69 percent of the daily oxygen lost from the upper section and 12 to 42 percent from the lower section of the metalimnion from June 17 to August 28, 1975.

The metalimnetic oxygen depletion of Boulder Basin is due to the oxygen consumption of the complete aquatic community of producers, consumers, and reducers. The zooplankton, representing the major consumers, account for a significant portion of the oxygen depletion.


Dissolved oxygen; Lake Mead (Ariz. and Nev.); Zooplankton


Biology | Environmental Indicators and Impact Assessment | Environmental Monitoring | Fresh Water Studies | Terrestrial and Aquatic Ecology | Water Resource Management