Colorado River Ecology and Dam Management Proceedings of a Symposium May 24-25, 1990 Santa Fe, New Mexico (1991) / Chapter Skim
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Algal and Invertebrate Biota in the Colorado River: Comparison of Pre- and Post-Dam Conditions
Algal and Invertebrate Biota in the Colorado River: Comparison of Pre- and Post-Dam Conditions
Pages 102-123
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From page 102... ...
, but was nearly clear during the low flows (113 m3 so ~ of late summer. The average suspended sediment load in the lower Colorado River before impoundment was 3.5 times higher than after the construction of Glen Canyon Dam (Dolan et al., 1974; Stanford and Ward, 1986; Stanford and Ward, this volume)
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From page 103... ...
The Green River is the largest tributary entering the Colorado River, and information collected before and after the closing of Flaming Gorge Dam is especially applicable to the events that have occurred in the Colorado River below Glen Canyon Dam (Pearson, 1967~. / POSTIMPOUNDMENT CONDITIONS Algal Communities Several algal surveys have been conducted in the Colorado River since the closure of Glen Canyon Dam in 1963.
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From page 104... ...
glomerata in the upstream tailwater sites may result from the abundance of stable rock surfaces for attachment and the clear, nutrient enriched waters from the hypolimnial releases of Glen Canyon Dam (Stanford and Ward, 1986~. The rather abrupt decrease in standing crop of C
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From page 105... ...
below Glen Canyon Dam, and therefore warrants further study. This filamentous green alga serves as a substratum for invertebrates and refuge from fish predators and fast-moving water.
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Zooplankton From Haury's (1986, 1988) analyses, it appears that zooplankters of the Colorado River below Glen Canyon Dam are derived from lentic populations in Lake Powell, i.e.
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From page 107... ...
There is good evidence that reproduction of zooplankton occurs in the river because microcrustaceans below the dam increase to at least the mouth of Diamond Creek, about 388 km below Glen Canyon Dam. Haury did note, however, that the percentage of copepod plankters in "poor condition" increased downstream.
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From page 108... ...
The faunal list includes species of planariid flatworm, perhaps three species of the Oligochaeta, gastropod molluscs of which Physa predominates, a clam possibly belonging to the Sphaeriidae, the amphipod crustacean Gammarus lacustris, and members of six insect families. A baetid mayfly (Baetis sp.)
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From page 109... ...
. Scuds do currently occur in Bright Angel Creek, and other tributaries entering the river below Glen Canyon Dam.
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From page 110... ...
Some references to sphaeriid clams in the Colorado River below Glen Canyon Dam may be referable to Corbicula from a different pelecypod family. Carothers and Minckley (1981)
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From page 111... ...
on the biomass and chlorophyll a of Cladophora glomerata in a simulated stream environment. Their study indicated that exposures of 12 daylight hours or longer resulted in significant reductions in C
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(1989a) examined the importance of elevated water temperature on the community structure of periphytic diatoms in the tailwaters (25 km below Glen Canyon Dam)
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From page 113... ...
of the Colorado River below Glen Canyon Dam. It is noteworthy that Ross and Rushforth (1980)
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From page 114... ...
It is noteworthy that Diatoms vulgare is one of the more common diatom taxa associated with regulated streams, including the tailwaters of Glen Canyon Dam, and is frequently epiphytic on Cladophora and prefers cool, flowing water with high nutrients (Lowe, 1979~. All of these conditions commonly prevail in the tailwaters of reservoirs.
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From page 115... ...
, extreme discharges can dislodge attached algal communities and severely reduce standing crop (Fisher et al., 1982; Skulburg, 1984; Power and Stewart, 1987; Duncan and Blinn, 1989~. It is likely that the Colorado River did not develop extensive algal populations prior to the closure of Glen Canyon Dam because of periodic scouring by turbid flood waters (Woodbury et al., 1959~.
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From page 116... ...
Modifications in thermal conditions also contribute to the compositional changes in macroinvertebrates below reservoirs. The thermal constancy and seasonal temperature patterns below dams may disrupt thermal signals essential for the completion of life cycles for certain macroinvertebrates.
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From page 117... ...
We recommend that, in cooperation with the Bureau of Reclamation, collections be made under different flow regimes (i.e., typical range of regulated discharge and steady flow) at several locations in the tailwaters of Glen Canyon Dam at various depths within the river channel to establish comparative baseline information on the population dynamics of this important primary producer under regulated flow in the Colorado River ecosystem.
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From page 118... ...
1986. Examination of the influence of elevated temperature on epiphytic diatom species in the tailwaters of Glen Canyon Dam and the importance of these epiphytic diatoms in the diet of Gammarus lacustris.
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1986. Zooplankton of the Colorado River from Glen Canyon Dam to Diamond Creek.
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1988. The utilization of Cladophora glomerata and epiphytic diatoms as a food resource by rainbow trout in the Colorado River below Glen Canyon Dam, Arizona.
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1976. Survey of phytoplankton, bacteria and trace chemistry of the lower Colorado River and tributaries in the Grand Canyon National Park.
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Creel census and limnological study of the Colorado River below Glen Canyon Dam.
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1959. Ecological studies of the flora and fauna in Glen Canyon.
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