All reservoirs have some distinct characteristics, but, in general, Rob Roy Reservoir and Lake Owen are unique, whereas Granite Springs and Crystal Lake Reservoirs are similar. Rob Roy is the highest in elevation, the largest in storage capacity, and the deepest. In contrast, Lake Owen has minimal storage capacity and is the shallowest of the four reservoirs. Both Rob Roy and Lake Owen are located in the Medicine Bow Mountains, Albany County; Granite Springs and Crystal Lake are located in the Laramie Mountains, Laramie County, about 45 miles to the east. Granite Springs and Crystal Lake are close to 7,000 ft above sea level, about 2,000 ft lower than Rob Roy and Lake Owen. Granite Springs and Crystal Lake have comparable storage capacities and similar depths. All four reservoirs are recreational areas.
A general comparison can be made among the profiles measured at Rob Roy, Granite Springs, and Crystal Lake. Lake Owen, due to its shallow depth, is not very comparable to the other three reservoirs and will not be discussed further in this section.
Rob Roy, Granite Springs, and Crystal Lake are dimictic reservoirs because they mix or "turn over" twice a year. In 1998, Rob Roy was always cooler, probably due to the high elevation, than either Granite Springs or Crystal Lake Reservoirs. In 1998, temperature in the hypolimnion zone in Rob Roy generally ranged from 5 to 10°C (fig. 5). By September 1998, the temperature in the hypolimnion was about 15°C in both Granite Springs and Crystal Lake. In 1998, the temperature in the epilimnion of Rob Roy reached a maximum of 16.7°C. During 1998 the maximum temperature in the epilimnion was 26.6°C in Granite Springs and 21.1°C in Crystal Lake. Rob Roy retained a stronger stratification in mid-September, 1998, in comparison to Granite Springs or Crystal Lake.
Granite Springs and Crystal Lake showed very similar thermal changes over time (figs. 17 and 20). Both reservoirs were unstratified in May, developed strong thermal stratification by mid-July, and stratification dissipated by early fall. It is most likely that the large volume of water that passes through Granite Springs and Crystal Lake reservoirs disrupts the more classic stratification pattern associated with temperate lakes. Whereas Rob Roy reservoir maintained temperatures below 8°C in the hypolimnion throughout the summer, much warmer temperatures (greater than 10°C) were measured in the hypolimnion of Granite Springs and Crystal Lake reservoirs.
September 1998 profiles (fig. 3C, 16D, 19D) show similar patterns of higher pH in the epilimnion, and lower pH in the hypolimnion. The pH also was greater in the two lower reservoirs than in the upper reservoirs: 6.5 to 7.5 in Rob Roy; 7.0 to above 8.0 in Granite Springs; and 7.0 to 8.5 in Crystal Lake. Dissolved oxygen during the same period was substantially different in Rob Roy (fig. 3C) than in Granite Springs and Crystal Lake (figs. 16D and 19D). Dissolved-oxygen concentrations in Rob Roy decreased from slightly higher than 7 mg/L to about 5 mg/L. In contrast, concentrations in both Granite Springs and Crystal Lake were slightly higher than 7.5 mg/L near the surface to about 26 ft and decreased to less than 1mg/L in the hypolimnion.
| The phytoplankton community was different in each reservoir. The average biomass and density of phytoplankton were lowest in Rob Roy, and the concentrations generally increased progressively from Lake Owen to Granite Springs and Crystal Lake (fig. 23A). The one exception to the pattern was that the average density was larger in Granite Springs than in Crystal Lake. The average concentrations are slightly skewed by a phytoplankton bloom in Granite Springs and to a lesser degree, blooms in Crystal Lake and Lake Owen (fig. 23B). The phytoplankton density followed the seasonal pattern of the biomass, although large concentrations of relatively small-sized Chrysophyta in Lake Owen caused a spike in density relative to biomass, as did large concentrations of relatively small-sized blue-green algae in Crystal Lake (fig. 23C). The biomass concentrations are considered a more reliable indicator of primary productivity because the size of the algae is not accounted for in the density estimate. | 
Figure 23. Phytoplankton biomass and density in Rob Roy
Reservoir and Lake Owen, Albany County, and Granite Springs and Crystal
Lake Reservoirs, Laramie County, Wyoming (A, average
boimass and average density; B, total biomass; and C,
total density). |
The composition of the phytoplankton community also was different between the upper and lower reservoirs. Many of the species found in Rob Roy and Lake Owen are associated with oligotrophic, nutrient-poor conditions. In contrast, many of the species found in Granite Springs and Crystal Lake are associated with mesotrophic (between poor and rich nutrient conditions) or eutrophic (nutrient-rich) conditions. As an example, blue-green algae were absent from the higher elevation reservoirs, but dominated some of the samples from the lower reservoirs. The species Anabaena , which is often associated with algal blooms, was the predominant species of blue-green algae in the lower reservoirs. Green algae, diatoms, and chrysophytes dominated the phytoplankton samples from the higher-elevation reservoirs. An abundance of desmids (a family of green algae) relative to other algae in oligotrophic lakes has been noted by Prescott (1968, p. 293). The desmids Cosmarium, Staurastrum , and Spondylosium were dominant or subdominant in some of the samples from Rob Roy, as described earlier in this report. Desmids also were present in Lake Owen and Crystal Lake, but at relatively smaller concentrations. Desmids typically are found sparingly in phytoplankton samples, with large numbers of species or individuals usually found only where the pH ranges from 5 to 6 (Smith, 1950, p. 310). The pH values at Rob Roy were the lowest of the four reservoirs studied and generally were less than 7.
Nutrient concentrations could be limiting phytoplankton growth in the reservoirs, based on samples collected in late August and early September 1997 (table 2). All concentrations of dissolved ortho-phosphorus were less than the reporting limit of 0.01 mg/L. For comparison, the U.S. Environmental Protection Agency (1986) recommends ortho-phosphate concentrations in lakes and reservoirs not exceed 0.025 mg/L for protection against aquatic nuisance algal blooms and to control accelerated or cultural eutrophication. Concentrations of dissolved nitrogen species generally were less than the reporting limits, particularly in the near-surface samples. Silica can be a limiting nutrient to diatoms, because they need silica to build their frustules. Concentrations of silica from the one set of surface samples collected in this study, however, were in the range of 2.1 to 5.8 mg/L, indicating adequate supplies of silica. Limiting concentrations of silica for certain diatoms are 0.5-0.8 mg/L (Reid and Wood, 1976, p. 244), and 0.5-1.0 mg/L (Prescott, 1968, p. 338).
The total number of taxa identified also increased downstream in the reservoirs: Rob Roy, 29 taxa; Lake Owen, 37 taxa; Granite Springs, 41 taxa; and Crystal Lake, 42 taxa. The green algae were the most diverse division, with a total of 34 taxa identified in this study. Some green algae, such as Chlorella, Quadrigula , and Sphaerocystis were found in all four reservoirs (table 4). Twenty taxa of green algae, however, were found in only one reservoir. Other taxa of algae found in all four reservoirs include the diatom Fragilaria , and the cryptomonads Campylomonas reflexa, Campylomonas rostratiformis, Katablepharis , and Plagioselmis . A total of 80 taxa were identified in the samples from this study.
The phytoplankton communities and water chemistry of Rob Roy and Lake Owen appear to be somewhat similar to those of Fremont and New Fork Lakes, two oligotrophic lakes in western Wyoming. The dissolved solids and nutrient concentrations in all four water bodies were similar to each other, except for silica, which was lower in Fremont Lake (median concentration 1.4 mg/L) (Peterson and others, 1987, p. 36-43). The average phytoplankton density was 4,840 cells/mL in Fremont Lake and 1,710 cells/mL in New Fork Lakes (Peterson and others, 1987, p. 26-29); this range is similar in Rob Roy and Lake Owen. Diatoms, green algae, golden-brown algae, and blue-green algae were common components of the phytoplankton community at Fremont and New Fork Lakes. In contrast, blue-green algae were not identified in Rob Roy or Lake Owen.
During 1983-84 and 1989, a total of 146 species were identified in samples from Fremont Lake (Averett and others, 1993). The larger number of species identified in Fremont Lake, compared to Rob Roy and Lake Owen, is due, at least in part, to two factors: (1) the wider scope of seasons, years, and depths sampled from Fremont Lake, and (2) the species-level identifications, as opposed to the mostly genus-level identifications from this study. Many of the same genera of algae were identified from all three-water bodies.
Secchi disk transparencies indicate that Rob Roy had the clearest water of the four reservoirs studied (fig. 4). The average transparency in each reservoir was:
|
Reservoir |
Secchi disk transparency |
Approximate euphotic zone thickness |
|---|---|---|
|
Rob Roy |
10.4 |
31 |
|
Lake Owen |
6.6 |
20 |
|
Granite Springs |
8.2 |
25 |
|
Crystal Lake |
6.1 |
18 |
The euphotic zone is the upper layer of the lake where sufficient sunlight penetrates for photosynthesis. The depth of the euphotic zone typically extended below the metalimnion when the reservoirs were stratified, indicating adequate light for photosynthesis throughout the epilimnion. For comparison, Secchi disk readings from Fremont and New Fork Lakes ranged from 10.5 to 49 ft (Peterson and others, 1987, p. 18-19).
The phytoplankton counts in the MPA are lower in Rob Roy then in Granite Springs and Crystal Lake. Rob Roy is at an elevation of 9,470 ft. The surface of the reservoir is frozen and snow-covered for most of the year, thereby, restricting sunlight and phytoplankton growth. Water flows from Rob Roy to Lake Owen where the MPA indicated less algae. Several factors at Lake Owen could influence it's phytoplankton counts. Lake Owen is shallow and vegetation is abundant. Also, Lake Owen contains some rotifers that may be consuming algae. Lake Owen may be acting as a wetland with the vegetation consuming the nutrients, thereby limiting the algal cell growth. The elevation of Crystal Lake Reservoir is 6,969 ft, allowing even more favorable conditions for algal growth.
Higher phytoplankton counts in the MPA are seen in both Granite Springs and Crystal Lake. Granite Springs is dominated by diatoms, whereas Crystal Lake had both non-diatomaceous phytoplankton and diatoms in the MPA. The warmer climate associated with the lower elevation of these two reservoirs, and the wind, which often keeps the ice from being covered by snow, are possible reasons for the higher phytoplankton counts. Investigation of the reasons for these differences is beyond the scope of this study.
Dissolved-solids (fig. 7) concentrations were slightly greater with depth within Rob Roy, Granite Springs, and Crystal Lake Reservoirs. The pattern was consistent in all three reservoirs although the amount of increase was small. Silica, as dissolved SO2, showed a consistent pattern of increasing with depth in Rob Roy, Granite Springs, and Crystal Lake (fig. 9), as did iron (fig. 10) and manganese (fig. 11).
| Dissolved-solids concentrations in Granite Springs and Crystal Lake were about double those of the upper two reservoirs, Rob Roy and Lake Owen (fig. 24). The concentrations of individual major ions were larger in the lower two reservoirs, but the percentages of major ions were similar (fig. 8). Thus, although the concentrations of individual dissolved constituents were larger in the two lower reservoirs, the major-ion concentrations occurred in about the same proportions. | 
Figure 24. Comparison of the concentration of major ions in
the surface samples collected in the fall of 1997 at Rob Roy Reservoir
and Lake Owen, Albany County, and Granite Springs and Crystal Lake
Reservoirs, Laramie County, Wyoming. |
Composite sediment samples were collected and analyzed from all four reservoirs (table 3). The major constituents analyzed were present in similar concentrations in all four reservoirs, except for nitrogen. Rob Roy and Lake Owen were similar with 9 and 8 mg/kg of nitrogen, reported as total nitrite plus nitrate. Granite Springs and Crystal Lake both had nitrogen concentrations less than the detection limit. In all four reservoirs, aluminum was 6.2 to 6.9 percent of the sediment. Iron concentrations in samples from all four reservoirs ranged from 2.2 percent to 3.6 percent. Phosphorus and titanium were present in similar concentrations in all four reservoirs.
Differences in bottom-sediment samples from the reservoirs were most apparent in the concentrations of trace elements. When thorium, vanadium, cerium and chromium concentrations were plotted (fig. 12), the samples fell into two groups. Sediment concentrations from Rob Roy and Lake Owen (Group l) are more like the crustal average than either diabase or granitic rocks. In contrast, the concentrations from Granite Springs and Crystal Lake Reservoirs (Group 2) are closer to concentrations present in granitic rocks.
Surface water contributes approximately 75 percent of the City of Cheyenne's drinking-water supply. Most of that surface water is provided by four reservoirs: Rob Roy, Lake Owen, Granite Springs, and Crystal Lake. Although extensive water-quality data are collected for the treated water, limited data were available on the raw-water quality within the storage reservoirs.
Rob Roy Reservoir is the largest, deepest, and highest in the series of the reservoirs. Profile measurements indicate that in 1998 Rob Roy was strongly stratified from mid-July into late September and by early October was no longer stratified. The zone of warming in Rob Roy extended progressively deeper into the reservoir from mid-July into September. Bacillariophyta (diatoms) and Chlorophyta (green algae) dominated the phytoplankton community of Rob Roy. Twenty-nine taxa of algae were identified from the samples, including eighteen taxa of green algae. In Rob Roy, the microscopic particulate analysis (MPA) was dominated by non-diatomaceous phytoplankton and diatoms. The water was a calcium-bicarbonate type with the lowest dissolved solids of the four reservoirs. Dissolved-solids and major-ion concentrations indicated little difference between the top and bottom samples of Rob Roy. Iron and manganese concentrations, however, were higher in the bottom sample. Concentrations of selected trace elements in bottom sediment from Rob Roy resemble the crustal average rock more than either diabase or granitic rocks.
Lake Owen is the shallowest and smallest of the series of reservoirs. It showed little stratification, probably due to its shallow depth and large surface area to volume ratio. Lake Owen warmed by mid-July in 1998 and cooled quickly in the fall. The golden-brown algae Chrysophyte dominated the phytoplankton community; Uroglenopsis was the most common species in the samples. Lake Owen is the only one of the four reservoirs in this study to have extensive macrophyte growths. In the fall of 1997, MPA was dominated by non-diatomaceous phytoplankton and diatoms, with a few rotifers being detected. Analysis of a single water sample, collected 1 foot below the reservoir surface, indicated the water quality was similar to that of Rob Roy, with a dissolved-solids concentration of 20 mg/L and of a calcium-bicarbonate type. Lake Owen had the largest concentration of dissolved iron of the four reservoirs. Like Rob Roy, bottom sediment from Lake Owen resembled crustal averages.
Granite Springs Reservoir is the third reservoir in the series and receives water through both Stage I and Stage II pipelines from Lake Owen. Profiles indicate that Granite Springs developed stratification by early-to-mid July; the reservoir was unstratified in the winter. The 1998 temperature profiles in Granite Springs indicate a seasonal progression of the water temperature in the reservoir from a uniform profile, to linear warming, to stratification, to a uniform profile. Diatoms and blue-green algae dominated the phytoplankton community. Blue-green algae, principally Anabaena, dominated the biomass of the algae in the August 1997 and July 14, 1998 samples. The two samples collected for chemical analysis indicated that the water was a calcium-bicarbonate type. Dissolved-solids concentration increased slightly with depth. Likewise, dissolved-iron and manganese concentrations increased with depth. The MPA was dominated by non-diatomaceous phytoplankton and diatoms. A few rotifers were detected. Trace-element concentrations in bottom sediment in Granite Springs resemble concentrations found in granitic rocks.
Crystal Lake Reservoir is the last reservoir in the series. Water flows down Middle Crow Creek and through a pipeline from Granite Springs into Crystal Lake. Profile data indicate that stratification occurred during the warmer months. Throughout the May and June period of 1998 the reservoir warmed and stratification developed. By mid-July, the reservoir was stratified and surface water temperature was slightly greater than 20°C. Blue-green algae and diatom biomass dominated the phytoplankton community. Of the 42 algal taxa identified, only 5 taxa were blue-green algae. The MPA was dominated by non-diatomaceous phytoplankton and diatoms. The three samples collected for chemical analysis at Crystal Lake indicated the water was a calcium-carbonate type with dissolved-solids concentrations varying from 58 mg/L at the surface to 63 mg/L at the bottom. Concentrations of dissolved iron and manganese increased with depth in Crystal Lake. Selected trace-element concentrations in bottom sediment were more like granitic rocks than either diabase or the crustal average.
A general comparison was made between the 1998 profiles measured at Rob Roy, Granite Springs, and Crystal Lake Reservoirs. Rob Roy was always cooler, probably due to it's higher elevation. In Rob Roy, the temperature in the epilimnion reached a maximum of 16.7°C. In Granite Springs and Crystal Lake, the maximum temperature in the epilimnion was several degrees warmer--26.6°C in Granite Springs and 21.1°C in Crystal Lake. The hypolimnion in Rob Roy remained between 5 to 10°C. By September 1998, the temperature in the hypolimnion was greater than 15°C in both Granite Springs and Crystal Lake. This difference may be a result of the large inflow and outflow in Granite Springs and Crystal Lake caused by water-supply withdrawals. Granite Springs and Crystal Lake showed similar thermal changes over time. Both were unstratified in May, developed strong stratification by mid-July, and the stratification dissipated by early fall.
The phytoplankton community changed progressively downstream in the four reservoirs. The average biomass and density of phytoplankton were smallest in Rob Roy, and the concentrations generally were progressively larger in Lake Owen, Granite Springs, and Crystal Lake. The composition of the phytoplankton community also changed downstream. Many of the species found in Rob Roy and Lake Owen are associated with oligotrophic, nutrient-poor conditions. In contrast, many of the species found in Granite Springs and Crystal Lake are associated with mesotrophic or eutrophic conditions. The total number of taxa identified also changed progressively downstream: Rob Roy, 29 taxa; Lake Owen, 37 taxa; Granite Springs, 41 taxa; and Crystal Lake, 42 taxa.
The reservoirs showed increases in concentrations of dissolved solids in the direction of water flow between the reservoirs. Dissolved-solids concentrations in the two lower reservoirs, Granite Springs and Crystal Lake, were more than twice the dissolved-solids concentrations in the upper two reservoirs, Rob Roy and Lake Owen. The water type in all four reservoirs was calcium bicarbonate. Silica, as dissolved SiO2, increased with depth in all four reservoirs. Major-ion concentrations were present in about the same proportion in all four reservoirs. Concentrations of dissolved iron and manganese were elevated in the bottom samples as compared to the surface samples in all three reservoirs (figs. 10 and 11).
Bottom sediment was examined because sediment particles can act as sites for ion exchange between aquatic and solid phases. Differences in the reservoir sediment samples were most apparent when concentrations of trace elements were examined. Concentrations of selected trace elements from Rob Roy and Lake Owen are more like the crustal average than concentrations in either diabase or granitic rocks. In contrast, the concentrations from Granite Springs and Crystal Lake more closely resemble concentrations present in granitic rocks.
Averett, R.C., Emmett, W.W., and Peterson, D.A., 1993, The phytoplankton of Fremont Lake, Wyoming: U.S. Geological Survey Water-Resources Investigations Report 92-4071, 64 p.
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Houston, R.S., and Orback, C.J., 1976, Geologic Map of the Lake Owen Quadrangle, Albany County, Wyoming: U.S. Geological Survey Geologic Quadrangle
Map GQ-1304, 1 sheet, scale 1:24,000.
Love, J.D., and Christensen, A.C., 1985, Geologic Map of Wyoming: U.S. Geological Survey, 3 sheets, scale 1:500,000.
McGauhey, P.H., 1968, Engineering Management of Water Quality: New York, McGraw-Hill Book Co., 295 p.
Mason, Brian, 1966, Principles of Geochemistry (3d ed.): New York, John Wiley & Sons, Inc., 329 p.
Moore, J.W., 1989, Balancing the Needs of Water Use: New York, Springer-Verlag, 267 p.
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Powell, S.T., 1964, Quality of Water, in Chow, V.T. (ed.), Handbook of Applied Hydrology: New York, McGraw-Hill Book Co., Section 19, 37 p.
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_____1978, How to know the freshwater algae: Pictured key nature series (3d ed.): Dubuque, Iowa, Wm. C. Brown Company Publishers, 348 p.
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[Table of Contents] [Abstract]
[Introduction]
[Rob Roy Reservoir]
[Lake Owen]
[Granite Springs
Reservoir] [Crystal Lake Reservoir]
[Summary]
[Appendix A]
[Appendix B]
