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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Limnology of Lake Powell and the Chemistry of the Colorado River
Limnology of Lake Powell and the Chemistry of the Colorado River
Pages 75-101
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From page 75... ...
WARD, Colorado State University, Fort Collins, Colorado INTRODUCTION Lake Powell is a large, dendritic reservoir that fills the Glen Canyon segment of the lower Colorado River. Operation of Lake Powell in turn controls the hydrodynamics of the Colorado River through the Grand Canyon National Parl: to Lake Mead.
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From page 76... ...
It is the second-largest reservoir in the United States, next to Lake Mead located cat 250 km downstream on the Colorado River. Full pool in Lake Powell was first reached on June 22, 1980.
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From page 77... ...
, and 60% of the annual water budget is received in May-July as a result of snowmelt in the headwaters (Irons et al., 1965; Evans and Paulson, 1983~. In 1922 the Colorado River Compact apportioned water allocation based on a virgin (preregulation)
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From page 78... ...
The Colorado River Compact divided the Colorado River into upper and lower basins at the confluence of the Paria and Colorado rivers, which is located cat 30 km downstream from Glen Canyon Dam. Note that during the period 1967-1983 only slightly more than the legal allocation to the lower basin (8.9 km3 = 7.2 million acre-feet)
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From page 79... ...
In essence, Lake Powell buffers delivery of water from the upper basin to the lower basin. In the decade of the 1980s, flows in the Colorado River system were generally well above the long-term average (Figure 5-2)
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From page 80... ...
Data are km3. River Inflow Colorado River San Juan River Losses Bank Storage Evaporation1 Outflow measured at Lee's Ferry Difference Reservoir storage 10.6408 1.6881 .7404 .6170 10.0818 2.247 1 corrected for precipitation and based on reservoir two-thirds full SOURCE: Modified from Jacoby et al., 1977.
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From page 81... ...
in response to the economics of hydropower (Figure 5-3~. TABLE 5-3 Hydrological, thermal, and sediment transport characteristics of the Colorado River below Glen Canyon Dam based on the 1941-1977 period of record.
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From page 82... ...
J~lI Flood ~~ -~' I ~ ~ 1 1 1 1 1 JFMAMJJASONDJ FMAMJJASONDJFMAMJJASONDJFMAMJJA SONDJF 1982 1983 1984 1985 1986 YEAR FIGURE 5-3 Inter- and intrayear variation in discharge of the Colorado River at Lee's Ferry as a consequence of hydropower and flood control operations at Glen Canyon Dam for the period 1982-1986. SOURCE: Modified from Potter and Drake, 1989.
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From page 83... ...
However, bottom water remains aerobic (i.e., >3 mg/liter dissolved oxygen) , owing primarily to advective circulation generated by saline underflows from the Colorado and San Juan rivers during low winter discharge (Johnson and Page, 1981~.
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From page 84... ...
The Little Colorado River, which joins the Colorado River within the Grand Canyon, and the Paria River can contribute heavy sediment loads to the river during short-term spates, but the sediment load of the Colorado River is now virtually controlled by retention in Lake Powell. The fluvial sediments entering Lake Powell are dominated by the montmorillinite clay lattice and have an average in situ bulk density of 1.5 with a mean grain density of 2.65 g/cm3 dry mass, based on analysis of cores (Potter and Drake, 1989; but see Kennedy [1965]
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From page 85... ...
However, the sediment-laden river waters usually interflow through the reservoir because advectively circulated flood waters are typically colder and more dense than the upper portions of the water column (Gloss et al., 1980, 1981~. Nitrogen, Phosphorus, and Silica Because of the patterns of seasonal stratification described above, nutrients such as nitrogen, phosphorus, and silica are most uniformly distributed within the water column of Lake Powell during the winter and early spring.
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From page 86... ...
Bioavailability of Particulate Phosphorus Because of the importance of the phosphorus budget to lakewide bioproduction, the question of how much of the incoming phosphorus load is actually biologically labile or bioavailable is especially relevant. As noted above, Colorado River suspended sediments may desorb 20-30 ~g/liter soluble reactive phosphorus (SRP)
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From page 87... ...
. TDS concentrations are extremely dynamic over time (i.e., similar to the pre-1960s period in Figure TABLE 5-4 Composition of the major ions contributing TDS in the Colorado River at Lee's Ferry compared to Lake Powell water discharged from Glen Canyon Dam.
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From page 88... ...
(Salinity in the Colorado River at Imperial Dam increased from 380 mg/liter during pristine times to 825 mg/liter by 1975 [Gardner and Steward, 19751. Salinity trend models indicate that additional water diver3000 2000 ~7 J (D 1 000 1 rat T ol 1940 1 950 ~ _ ~ — _= 1970 1980 1990 YEAR FIGURE 5-4 Average annual concentrations of TDS derived from daily measurements at the tributary sites shown in Figure 5-1 for the period 1941-1987.
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From page 89... ...
Thus, pre- and post-dam salinities in the Colorado River at Lee's Ferry are about the same (Table 5-4) (Reynolds and Johnson, 1974; Gloss et al., 1980~.
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From page 90... ...
Given the size of the reservoir and the inaccuracies of loading estimates, it is doubtful that the actual impact of calcite precipitation on salinity trends in the Colorado River will be verified from mass balance calculations. That the rate of calcite precipitation in Lake Powell is influenced by fluvial salt loading, bed dissolution of CaSO4, phytoplankton productivity, and polyphenol inhibition (Reynolds, 1978)
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From page 91... ...
. Chlorophyll concentrations in the water column averaged 5 ,ug/liter near the Colorado River and 1.5 ,ug/liter lakewide during 1982-1983 (Paulson and Baker, 1983a)
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From page 92... ...
Zoop lank ton Stone and Rathbun (1969) reported that Daphnia, Cyclops, and Diaptomus were dominant zooplankters with densities that varied between 15 and 100 individuals per liter in the upper 30 m of the water column.
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From page 93... ...
were primary food items in guts of Merone saxatalis (striped bass) that spawned in the mixing zone of the Colorado River.
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From page 94... ...
These trees and bushes occur commonly on the rim and flanks of Glen Canyon and, prior to impoundment, graded into terrace flora that included deep-rooted shrubs (such as four-winged saltbrush [A triplex
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From page 95... ...
Materials balance calculations show that most of the sediments and most of the phosphorus and other metals entering the reservoir are retained in the basin either in the profundal waters and sediments or in bank storage. Thus, the reservoir sequesters the solids load of the Colorado River.
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From page 96... ...
However, it is clear that the presence of Lake Powell has vastly altered the chemistry and bioproduction of both the Colorado River and Lake Mead.
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From page 97... ...
Thus, it seems reasonable to expand the idea of the Glen Canyon area as an ecosystem (Marzolf et al., 1987) to include the tributaries of Lake Powell, the reservoir itself, the Colorado River from Glen Canyon Dam to Lake Mead, and Lake Mead.
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From page 98... ...
1983. The influence of Lake Powell on the suspended sediment-phosphorus dynamics of the Colorado River inflow to Lake Mead, p.
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From page 99... ...
1965. Water resources of the Upper Colorado River Basin - Technical Report.
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From page 100... ...
1982. Feeding activity and spawning time of striped bass in the Colorado River inlet, Lake Powell, Utah.
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From page 101... ...
Hydrobiologia 49:1 1 1-1 16. Upper Colorado River Commission.
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