River Resource Management in the Grand Canyon (1996) / Chapter Skim
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6 ORGANISMS AND BIOLOGICAL PROCESSES
6 ORGANISMS AND BIOLOGICAL PROCESSES
Pages 84-117
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From page 84... ...
studies of the Colorado River between the Glen Canyon Dam and the Paria River (26 km)
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From page 85... ...
Thus, any comprehensive assessment of the Colorado River below Glen Canyon Dam must include Lake Powell (Figure 6.1~. Lake Powell has been studied by several organizations and individuals over more than 20 years.
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From page 87... ...
Although Lake Powell receives a very large amount of water from the Colorado and San Juan rivers, as well as a small amount from the Dirty Devil River, the large size of the reservoir allows a mean water retention time of approximately 2 years (Table 6.1~. The residence time of the reservoir is sufficiently long to allow complete sedimentation of the inorganic material that enters it at the upper end.
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From page 88... ...
In Lake Powell the distinction between metalimnion and hypolimnion istypicallyunclearforthis reason. The summer epilimnion (mixed layer)
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From page 89... ...
10 0 a, O O _ it_ AL O 0, Dissolved Oxygen, mg/liter 2 4 68 10 , , ,~ O ~ O _ O f ·: FIGURE 6.2 Profiles of temperature, conductance, and dissolved oxygen for Lake Powell near the dam at Waheap (unpublished data from the BOR)
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From page 90... ...
Increase in volume of the lower layer is offset by erosion from the top of the layer under the influence of wind mixing and by withdrawal of water through the Glen Canyon Dam outlet structure. If water in the lower layer were not replaced, or were to be replaced more slowly than at present, the lower layerwould become anoxic, and anoxic water could pass downstream, where it could adversely affect trout and other organisms.
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From page 91... ...
During warm weather, dissolved phosphorus may be essentially depleted within 50 to 100 km of the dam in the upper water column. Thus, phosphorus probably limits primary production in Lake Powell near the dam, while shading caused by turbidity probably limits primary production in the upper portion of the lake (Gloss et al., 1980~.
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From page 92... ...
Concentrations of heavy metals in Lake Powell are potentially of interest with respect to the biota of the lake as well as aquatic communities downstream. Concentrations of mercury in the water column of the lake appear to fall within the range that might inhibit growth of primary producers and may have other biological effects downstream (Graf, 1985; Blinn et al., 1977a)
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From page 93... ...
There is at present no reason to believe that any possible operating plan with the current facilities would have a distinctive influence on Lake Powell. If new facilities, such as a multiple outlet withdrawal structure or slurry pipeline, were to be installed, however, the possible effects of these structures on Lake Powell would become relevant to dam operations.
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From page 94... ...
The original Colorado River was subject to surges in flow and turbidity corresponding to the flooding of tributaries associated with convectional storms. Such surges can still occur, especially below the Little Colorado River, but are reduced in frequency because of the interception of storm flows above Glen Canyon Dam by Lake Powell.
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From page 95... ...
! it ,~ \ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 o° o° o° To To o boo' ~oO ~oO ~oO oOO o ~o° ~o° Of A ° Time of Day FIGURE 6.3 Discharge at two locations on the Colorado River just below Glen Canyon Dam and at Diamond Creek (both on May 10-12, 1994~.
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From page 96... ...
The absence of suspended sediment in the water leaving Lake Powell has led to progressive removal of sand and finer particles from the channel and sides of the Colorado River between the Glen Canyon Dam and the Paria River. Thus, the bottom of this segment of river has an abundance of coarse
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From page 97... ...
The biological studies of GOES have shown that the conditions of the Colorado River below Glen Canyon Dam and above Lake Mead are so inherently unsuitable for reestablishment of native fishes that a strong argument could be made for the management of this segment of the river exclusively for trout. The opposite is true downstream, as shown by the progressive disappearance of trout and a shift toward greater presence of native fishes and warmwater exotics such as carp.
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From page 98... ...
Cladophora below Glen Canyon Dam is coated with a growth of diatoms (Blinn and Cole, 1991~. Thus, Cladophora is significant not only for its own sake but also in providing substrate for the growth of other algae that may be more significant in the food chain.
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From page 99... ...
The dominant fish species at present either numerically or in terms of biomass in the Glen Canyon reach is the rainbow trout (Onchorhynchus mykiss) , which is sustained by the perennially cold water originating from the depths of Luke Powell.
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From page 100... ...
, it was not studied during Phase 11 of GCES. THE COLORADO RIVER FROM THE PARIA RIVER TO LAKE MEAD Physical Characteristics The Paria River begins to reverse some of the effects of Glen Canyon Dam as observed in the upper segment, and the Little Colorado River reinforces this trend downstream.
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From page 101... ...
The predominantly sandy substrate, which is poor habitat for most invertebrates, and the low abundance of Cladophora, which supports the large amphipod populations of the upper reach, presumably explain the decline in abundance of invertebrates below the Paria and the Little Colorado River. The Colorado River between Glen Canyon Dam and Lake Mead was once the habitat of a highly specialized fish fauna.
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From page 102... ...
Changes in the fish community began well before Glen Canyon Dam was installed, but the thermal and physical effects of the dam have undoubtedly exacerbated earlier changes caused mainly by exotic species and land use or depletion of tributary flow (Miller, 1961; Minckley, 1991~.
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From page 103... ...
Backwaters include inundated off-channel areas as well as return channels associated with eddies and main-stem flow blockages behind debris. Off-channel backwaters are relatively rare in the Grand Canyon but may be important in providing nursery areas for warmwater fishes because of their warmth and low current velocities.
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From page 104... ...
As shown by the BioWest studies, adult humpback chub are strongly associated with eddies, which probably provide an accumulation of food in a region of relatively low current velocity (\/aldez and Ryel, 1995~. Tributary junctions are perhaps the most significant aquatic habitat in the entire Colorado River system below Glen Canyon Dam.
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From page 105... ...
Temperature may be the most critical change, given that the humpback chub is a warmwater fish, but water clarity, availability of backwaters, seasonality of flow, and presence of exotic species are also important (Valdez and Ryel 1995~. The humpback chub has survived below Glen Canyon Dam by using the Little Colorado River and other tributaries as warmwater refuges for spawning and maintenance of young fish (USFWS, 1993~.
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From page 106... ...
Aside from the five native species, the lower segment of the Colorado below Glen Canyon Dam contains about 20 exotic species (Minckley, 1991~. In fact, introduced species are considerably more abundant than native species either numerically or in terms of biomass.
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From page 107... ...
The welfare of the humpback chub and other native species along the Colorado River will depend on environmental changes not only in the Grand Canyon but also in tributaries of the Colorado. Biotic Interactions Competitive and predatory interactions involving native and exotic species might well be influenced by the operation of Glen Canyon Dam.
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From page 108... ...
, with emphasis on the area near the dam, and studies of the humpback chub in the main stem by BioWest (\/aldez and Ryel, 1995) are examples of wellexecuted projects with specific and useful outcomes.
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From page 109... ...
, but not between the Little Colorado and Glen Canyon Dam. Riparian characteristics associated with proximity to surface water and with the availability of ground water near the surface are the basis for maintenance of characteristic vegetation and associated riparian species below Glen Canyon Dam.
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From page 110... ...
OUTCOMES OF BIOLOGICAL STUDIES GCES provided much new information on the biotic resources of the Colorado River below Glen Canyon Dam. The abundances and distributions of many kinds of organisms were quantified satisfactorily for the first time.
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From page 111... ...
For example, GCES showed that large rapid fluctuations in discharge interfere with spawning of trout near Glen Canyon Dam and strand some adult fish. At the same time, however, such variations appear to dislodge food items that in this way become vulnerable to trout.
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From page 112... ...
1995a. Water Chemistry and Zooplankton in the Lake Powell Forebay and the Glen Canyon Dam Tailwater.
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From page 113... ...
1994. Effects of Glen Canyon Dam on Colorado River Sand Deposits Used as Campgrounds in Grand Canyon National Park, USA.
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From page 114... ...
1993. Impacts of fluctuating water levels on eggs arm fry of rainbow trout in the Colorado River below Glen Canyon Dam, Arizona.
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From page 115... ...
Pp. 217-228 in Glen Canyon Environmental Studies: Executive Summaries of Technical Reports.
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From page 116... ...
1994. The Effects of Interim Flows from Glen Canyon Dam on Riparian Vegetation Along the Colorado River in Grand Canyon National Park, Arizona.
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From page 117... ...
in the Colorado River: Glen and Grand Canyons. Glen Canyon Environmental Studies Technical Report.
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