The purpose of this investigation was to identify the zooplankton arc.
phytoplankton found in Lake Mead, to quantify their presence, to elucidate
some temporal and spatial patterns, and to investigate some of the planktonic
responses to physical, chemical, and biological parameters.
Phytoplankton and zooplankton population samples were collected from
eight different sites at 11 depths at six times over an annual period.
These samples were collected with a 6 -liter Van Dorn sampler. Phytoplankton
samples were preserved in Lugol's solution and the zooplankton
were placed in formalin preservative. The 503 zooplankton population
samples were scored in a ruled counting chamber using a stereomicroscope.
Eighteen species of zooplankton were identified. The 274 phytoplankton
samples were placed on Millipore filters and slides were prepared for
examination with phase contrast microscopy. A total of at least 79 algae
were found to comprise the phytoplankton flora.
The zooplankton for the most part were rotifers, cladocerans, and
copepods. Keratella, the principal rotifer, was found to be diacmic and
Bosmina, Daphnia, the calanoid, cyclopoid, and nauplii copepods were
monacmic. Spatial relationships across the reservoir indicate that Bosmina
and cyclopoid copepods are water quality indicators. The late summer
phytoplankton were mostly Cyanophyta with populations as large as 5 X 106
cells /liter occurring in Boulder Basin. Winter samples contained mostly
diatoms and cryptomonads, while the spring phytoplankton was mainly
Chlorophyta. The early summer flora showed a mixture of Chrysophyta,
Chlorophyta, and Cryptophyta.
Biomass determinations were made from average cell volumes and population
counts. The blue -green alga Oscillatoria had the greatest biomass
during the late summer period. Bacillariophyta reached a volumetric peak
in late winter and the Chlorophyta in spring. The Cryptophyta showed a
peak in winter while the Chrysophyta, represented mostly by the presence
of Dinobryon, showed greatest population sizes in early summer. The
Euglenophyta and Pyrrophyta were relatively unimportant groups of the biomass.
Weak nocturnal migrations were exhibited by Asplanchna sp., Keratella
cochlearis, and Bosmina longirostris. This conclusion was derived from an
analysis of variance of the diurnal data. The copepod groups showed no
migration patterns. Since this study was performed when the lake was
isothermal, it is inferred that migration is a phenomenon not influenced
by temperature.
A transect study in Boulder Basin during the winter showed that
Daphnia, Asplanchna, Chydorus, and Polyarthra, and possibly calanoid copepods,
appear to be littoral, and are found mostly in the Las Vegas Wash
area. Phytoplankton counts showed evidence for decreases in Bacillariophyta,
Chlorophyta, Cyanophyta, and Cryptophyta across the basin from the
wash to the dam area. Pyrrophyta, Chrysophyta, and Euglenophyta were not
important in the phytoplankton flora at this season. Nygaard's and Pearsall's ratios and Palmer's pollution -tolerant algae
indices were applied to the phytoplankton data. Results of the Nygaard
and Pearsall ratios, the migration study, the transect study, and the
population studies indicate that Boulder Basin is eutrophic.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/620098 |
| Date | 06 1900 |
| Creators | Staker, Robert Dale |
| Contributors | Department of Hydrology & Water Resources, The University of Arizona |
| Publisher | Department of Hydrology and Water Resources, University of Arizona (Tucson, AZ) |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Technical Report |
| Source | Provided by the Department of Hydrology and Water Resources. |
| Rights | Copyright © Arizona Board of Regents |
| Relation | Technical Reports on Hydrology and Water Resources, No. 22 |
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