TWIN LAKES

An aerial view of the whole lake from the northeast

Photo.
Photo: J. F. LaBounty  
 

A. LOCATION

Colorado, USA.
39:5N, 106:0W; 2,804 m above sea level.

B. DESCRIPTION

Twin Lakes are located on the eastern slope of the Rocky Mountains in western North America. They lie at an altitude of 2,804 m above mean sea level, in the Montane Life Zone of Colorado. Twin Lakes are a pair of connected lakes which were originally formed by the morainal damming of Lake Creek by a Pleistocene glacier. This creek, a small tributary of the Arkansas River, was the main source of inflow to the lakes in their natural state.
The Lake Creek watershed is relatively small, with an area of only 238 km2. While the lakes themselves lie in deposits of glacial till, Lake Creek drains mainly the crystalline rocks and eroded ore bodies of the eastern slope of the Sawatch Range, along the Continental Divide. Consequently, the deeper sediments of both lakes, which are composed of a fine glacial rock flour, have accumulated large quantities of heavy metals, including iron, manganese, copper, zinc, lead, and cadmium.
The climate here is cool and semi-arid. Twin Lakes are dimictic, with an ice cover usually lasting from early December to early May in an average year. Maximum ice thickness ranges from about 60 cm, in an average year, to a meter or more during severe winters. Summer thermal stratification normally reaches its maximum in August, with surface water temperatures in the range of 15¡¦to 18¡¦, and bottom temperatures of about 9¡¦.
Upper Twin Lakes had a normal surface elevation nearly 2 m higher than the lower lake, and the natural fluctuation of surface elevation in each lake probably did not exceed 0.6 m annually. The normal surface area of the upper lake was about 220 ha, with a corresponding maximum depth of about 25 m. Lower Twin Lakes was larger in surface area, about 610 ha, but more shallow, with a maximum depth of about 23 m. Both lakes were probably oligotrophic, but they harbored diverse zooplankton and fish communities. One species of native trout was described as being endemic to Twin Lakes.
Permanent settlement began in this area in the late 1870's, and almost immediately the settlers began changing the ecology of Twin Lakes through the introduction of exotic species, and by modifications of the hydraulic regime, which were aimed at converting the lakes into water-supply reservoirs for irrigation and mining.
Since the turn of the century, a series of hydraulic engineering works had converted Twin Lakes into a pair of connected reservoirs. First, the natural outlet of the lower lake was dammed, and a deeper, gated outlet was constructed about 1 km to the north. This arrangement allowed a potential vertical fluctuation of 7.8 m in the water surface elevation of the lower lake. Next, the stream connecting the lake was dredged into a channel that allowed the two bodies of water to fluctuate essentially as one. Finally, a tunnel was constructed under the Continental Divide to divert water from the western slope into Lake Creek. This transmountain diversion increased the total annual discharge of Lake Creek by an average of 42%. It is important to note here that this additional inflow was all added during the irrigation season, which extends from approximately June through September. Thus, the extra flow had the effect of increasing and prolonging the natural runoff peak in Lake Creek.
The net result of these hydraulic changes was increased erosion in the inflow area of the upper lake. What had originally been a marshy meadow was now an eroded floodplain, and the resulting woody debris was deposited in the bottom of Upper Twin Lakes. During severe winters, with prolonged ice and snow cover, this allochthonous organic deposit exerted a biochemical oxygen demand that resulted in extreme hypolimnetic anoxia, with toxic metal releases from the sediments. Primary production in the upper lake was also limited by intense flushing and turbidity during the spring runoff period. In fact, the upper lake functioned as a settling basin and buffer for the lower lake (1).

C. PHYSICAL DIMENSIONS (3, 6)

     
    Basin Upper Lake Lower Lake*
    Surface area [km2] 3.8 7.4
    Volume [km3] 55 0.118
    Maximum depth [m] 30.2 29.3
    Mean depth [m] 14.5 16.0
    Normal range of annual water
    level fluctuation [m] 2.5-4.5
    Length of shoreline [km] 10.7 13.7
    Residence time [yr] 0.47
    Catchment area [km2] 238
    * This is after raising of lake levels behind new dam in October 1983.
 

D. PHYSIOGRAPHIC FEATURES

D1 GEOGRAPHICAL
Sketch map: Fig. NAM-21-01.
Names of main islands: None.
Number of outflowing rivers and channels (name): 1 (Lake Creek).
D2 CLIMATIC
Climatic data at Station 3*, 1982 (1, 2) 
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann.
-7.8 - - - 5.2 9.7 13.4 13.3 9.0 2.4 -3.1 -5.9 2.3
Precipitation [mm]
     
    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann.
    34 - - - - - 69 - - - - - 469
     
* Lower Lake.
Solar radiation [MJ m-2 day-1](1, 2)
     
    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann.
    10.0 - - - 28.2 27.3 26.6 26.8 21.4 21.5 - - 11.8
     

    Fig. NAM-21-01
    Sketch map (2).
 

Water temperature [deg C](2)
Station 4*, 1982
[m]

     
    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann.
    1 - - - - 7.2 8.0 11.4 14.7 12.5 7.2 4.7 -
    13 - - - - 6.9 6.8 7.5 8.4 9.0 7.8 5.3 -
     
* Upper Lake.
Station 2*, 1982
[m]
     
    Depth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    1 - - - - 7.4 9.4 13.9 15.4 N.A. 8.8 5.6 -
    13 - - - - 6.5 8.9 10.1 11.0 11.7 8.9 5.2 -
     
* Lower Lake.

    Fig. NAM-21-02
    Temperature isopleths for Station 4 in Upper Lake during 1982 (2).
 

Freezing period: Early December-early May. 

E. LAKE WATER QUALITY

E1 TRANSPARENCY [m](3)
Station 4*1, 1972-1975
     
    Depth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S*2 - - - - - - 1.9 4.1 6.5 - - -
    E*3 - - - - - 4.3 5.1 7.3 9.7 11.2 11.2 -
     
*1 Upper Lake. *2 Secchi depth. *3 Euphotic depth.
Station 2*, 1972-1975
     
    Depth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S - - - - - 3.5 4.6 4.2 5.0 3.5 4.0 -
    E - - - - 9.1 8.2 9.8 9.9 11.0 9.8 - -
     
* Lower Lake.
E2 pH (2)
Station 4*, 1982
[m]
     
    Depth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    1 - - - - 6.83 6.74 6.64 6.98 6.92 6.81 7.12 -
    13 - - - - 6.84 6.48 6.37 6.37 6.34 6.74 6.9 -
     
* Upper Lake.
Station 2*, 1982
[m]
     
    Depth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    1 - - - - 6.7 7.45 7.60 7.87 7.42 7.12 7.0 -
    13 - - - - 6.9 6.97 6.68 6.65 6.55 7.16 7.35 -
    * Lower Lake.
E4 DO [mg l-1]: Fig. NAM-21-03 and 04.

    Fig. NAM-21-03
    Dissolved oxygen isopleth for Station 4 in Upper Lake during 1982 (2).
 

    Fig. NAM-21-04
    Dissolved oxygen isopleths for Station 2 in Lower Lake during 1982 (2).
 

E6 CHLOROPHYLL CONCENTRATION [micro g l-1](2)
Upper Lake, 1982
[m]

     
    Depth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.1 - - - - - - 0.49 - - - 5.26 -
    1.0 - - - - - - - - - - - -
    3.0 2.79 - 2.10 - - 0.96 - - - 3.43 - -
    5.0 1.49 2.00 - 2.35 - 1.24 - - 2.45 2.67 4.45 -
    9.0 - - - 2.19 1.92 - 0.97 1.43 1.70 - - -
     
Lower Lake, 1982
[m]
     
    Depth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.1 3.55 - - - - - - - - 4.65 6.22 -
    1.0 - - 2.05 - - - - - - - - -
    3.0 2.41 2.37 3.04 - - 2.93 - - - - - -
    5.0 - 2.33 - - - 3.07 - 3.03 - 5.61 6.87 -
    9.0 - - - 2.75 3.73 - 2.76 3.46 3.55 - - -
    15.0 - - - 2.77 3.24 2.66 - - - - 6.71 -
     
Chlorophyll a [mg m-2]
Upper Lake, 1982
[m]
     
    Depth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    31.95  31.83  31.11 35.59  34.72  15.77  10.08  24.83 32.30  45.37  70.73  -
     
Lower Lake, 1982
[m]
     
    Depth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    44.16 36.69  37.69 42.65  55.78 44.74 42.34 53.20 55.06 76.79  99.74  -
     
E7 NITROGEN CONCENTRATION (2)
NO3-N [mg l-1]
Upper Lake, 1982
[m]
     
    Depth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S*1 .038 - - - .060 - .032 - - .048 - -
    M*2 .038 - - - .090 - .038 - - .048 - -
    B*3 .042 - - - .010 - .056 - - .048 - -
     
*1 Surface. *2 Middle. *3 Bottom.
Lower Lake, 1982
[m]
     
    Depth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S <.001 - - - .020 - .010 - - .010 - -
    M <.001  - - - .021 - .015 - - .010 - -
    B .004 - - - .068 - .041 - - .010 - -

     

    Fig. NAM-21-05 NO3-N concentration in Twin Lakes and Lake Creek during 1982 (2).

    Fig. NAM-21-06
    Mean nitrate concentration (1).
 

E8 PHOSPHORUS CONCENTRATION (2)
Total-P [mg l-1]
Upper Lake, 1982
[m]

     
    Depth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S*1 .003 - - - <.001 - <.001 - - <.001  - -
    M*2 .004 - - - <.001  - <.001 - - <.001  - -
    B*3 .002 - - - <.001  - <.001 - - <.001  - -
    *1 Surface. *2 Middle. *3 Bottom.
Lower Lake, 1982
[m]
     
    Depth Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    S .004 - - - .005 - .003 - - <.001  - -
    M .021 - - - <.001 - .002 - - <.001  - -
    B .006 - - - <.001  - .001 - - <.001  - -
     

    Fig. NAM-21-07
    Total-P concentration in Twin Lakes and Lake Creek during 1982 (2).
 

    Fig. NAM-21-08
    Mean total phosphorus concentration (1).
 

E10 PAST TRENDS: Fig. NAM-21-09 and 10.

    Fig. NAM-21-09
    Annual inflow volume (1).
 

    Fig. NAM-21-10
    Thermal stratification (l).
 
 

F. BIOLOGICAL FEATURES

F1 FLORA
Emerged macrophytes: None.
Floating macrophytes: None.
Submerged macrophytes (4, 7)
Potamogeton amplifolius, P. praelongus, Chara globularis, Chara sp., Nitella opaca, Elodea sp.
Phytoplankton (5)
1976
Chysophyta (Dinobryon cylindricum, Mallomonas elongata, M. pseudocoronata), Chlorophyta (Dictyosphaerium pulchellum, Sphaerocystis schroeteri, Staurastrum longiradiatum), Bacillariophyta (Asterionella formosa, Synedra amphicephala, S. delicatissima, S. radians, S. ulna var. danica, Tabellaria flocculosa), Cyanophyta (Oscillatoria amphibia, O. tenuis).
F2 FAUNA
Zooplankton (5)
1974-1982
Cladocera (Daphnia pulex*, D. rosea*, Bosmina longirostris*), Copepoda (Diaptomus judayi*, D. connexus*, Cyclops bicuspidatus thomasi*), Rotifera (Kellicottia longispina*, Keratella cochlearis*, Polyarthra sp., Brachionus sp.), Mysidacea (Mysis relicta).
* Organisms examined for species identification.
Benthos
Chironomidae, Oligochaeta. Pisidium casertanum, P. pauperculum. Mysis rest on the bottom during daylight hours and are sometimes captured in benthic dredges. but they move into the water column to feed at night. They are more zooplankton than benthos.
Fish (4)
Salvelinus namaycush*, Salmo gairdneri*, S. trutta, S. clarki, Catostomus commersoni, C. catostomus, Oncorhynchus nerka.
* Important for sport-fishing.
F3 PRIMARY PRODUCTION RATE [mg C m-2 hr-1](2)
Determined by 14C technique
Upper Lake, 1982
Net production
     
    Ann.
    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec total
    2.9 1.8 2.7 2.1 5.4 2.4 0.6 3.6 4.0 2.8 2.0 - 12,825
     
Lower Lake, 1982
Net production
     
    Ann.
    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec total
    2.3 2.3 3.8 0.5 10.3 8.2 9.7 5.5 9.7 9.0 6.1 - 24,780
     
F4 BIOMASS (2)
Benthos
Upper Lake, 1982
     
    [No. m-2]* [g (dry wt.) m-2]*
    Chironomids 270 0.50
    Oligochaetes 1,585 0.33
    Pisidium spp. 54 0.03
    Mysis relicta 6 0.01
     
Lower Lake, 1982
     
    [No. m-2]* [g (dry wt.) m-2]*
    Chironomids 762 0.85
    Oligochaetes 536 0.11
    Pisidium spp. 651 0.64
    Mysis relicta 37 0.05
     
* 3 samples.

    Fig. NAM-21-11
    Special composition of phytoplankton population in Twin Lakes during 1982 (2).

 

    Fig. NAM-21-12
    Species composition of zooplankton population in Twin Lakes during 1982 (2).
 

F6 PAST TRENDS: Fig. NAM-21-13, 14, 15, 16, 17 and 18 (2).

    Fig. NAM-21-13
    Annual areal primary productivity rates for Upper Lake and Lower Lake.
 

    Fig. NAM-21-14
    Comparison of average plankton densities, 1979-1982.
 

    Fig. NAM-21-15
    Average abundance of four types of benthic organisms in Upper Lake, 1979-1982.
 

    Fig. NAM-21-16
    Average abundance of four types of benthic organisms in Lower Lake, 1979-1982.
 

    Fig. NAM-21-17
    Average dry mass of four types of benthic organisms in Upper Lake, 1979-1982.
 

    Fig. NAM-21-18
    Average dry mass of four types of benthic organisms in Lower Lake, 1979-1982.
 
 

G. SOCIO-ECONOMIC CONDITIONS (8)

G1 LAND USE IN THE CATCHMENT AREA
1989
     
    Area [km2] [%]
    Natural landscape
    Woody vegetation 118
    Herbaceous vegetation 19
    Swamp 5
    Alpine tundra-rock 94
    Residential area <2 <1
    Total 238 100
     
Types of important forest: Fir, pine, aspen and sagebrush.
Types of important herbaceous vegetation: Bunch grasses and sedges.
Types of the other important vegetation
Alpine vegetation (mat and cushion plants, dwarf willows).
Main kinds of crops: None.
Levels of fertilizer application on crop fields: None.
Trends of change in land use
Area immediately around lakes taken over as forest service managed camping and picnic areas. Private cabins and resort facilities removed. Some new cabins built in areas further away from lakes on private land.
G2 INDUSTRIES IN THE CATCHMENT AREA AND THE LAKE
1989: None.
G3 POPULATION IN THE CATCHMENT AREA
1989
     
    Population Major cities
    Population density [km-2] (population)
    Urban None
    Rural ca. 100-200* Twin Lakes
    Total
     
* Depending on season - more in summer.

H. LAKE UTILIZATION (8)

H1 LAKE UTILIZATION
Source of water, sight-seeing and tourism (in summer 1988, 16,201 visited Mt. Elbert powerplant visitor's centre - summer only 3 months) and recreation (sport-fishing in summer and ice-fishing in winter).
H2 THE LAKE AS WATER RESOURCE
     
    Use rate [m3 day-1]
    Domestic &
    Industrial*1 100,482
    Irrigation 113,557/ha irrigated annually.
    Power plant*2  200 MW
     
*1 These 2 are lumped by the Bureau as "M & I" (municipal and industrial) water.
*2 Pumped-storage hydroelectric plant.

I. DETERIORATION OF LAKE ENVIRONMENTS AND HAZARDS (8)

I1 ENHANCED SILTATION Extent of damage: None.
I2 TOXIC CONTAMINATION Present status: None.
I3 EUTROPHICATION
Nitrogen and phosphorus loadings to the lake [kg day-1]
1984
     
    Sources Natural Total
    DIN 52.7 52.7
    T-P 6.8 6.8
     
Supplementary notes: Lake is oligotrophic.
I4 ACIDIFICATION
Extent of damage: None.
I5 OTHER HAZARDS
Potential for release of heavy metals from sediments during extreme winter anoxia - Fe, Mn, Cu, Zn, especially. Sediment accumulations are result of glacial action and erosion on natural ore bodies in the watershed.

J. WASTEWATER TREATMENTS (8)

J1 GENERATION OR POLLUTANTS IN THE CATCHMENT AREA
    a) Pristine lake environments.
 

K. IMPROVEMENT WORKS IN THE LAKE (8)

None.

L. DEVELOPMENT PLANS (8)

U.S. Forest Service manages area for camping, picnicking, hiking - outdoor recreation. Colorado Division of Wildlife manages sport.fishing of the lakes - mostly stocked rainbow trout (Salmo gairdneri) and self-sustaining lake trout (Salvelinus namaycush).

N. SOURCES OF DATA

  1. Questionnaire prepared by the editors with the support of Dr. J. F. LaBounty, Environmental Sciences Section, Bureau of Reclamation, United State Department of the Interior, Denver, Colorado, based on the following sources.
  2. Sartoris, J. J. (1988) Twin Lakes, Colorado, USA: Ecological studies of the effects of pumped-storage hydroelectric development on a pair of Montane Lakes. Report to the Third International Conference on the Conservation and Management of Lakes "Balaton '88", Keszthely, September 1988.
  3. LaBounty, J. F., Sartoris, J. J. & Lieberman, D. M. (1984) Effects of Operating Mt. Elbert Pumped-Storage Powerplant on Twin Lakes, Colorado: 1982 Report of Findings. U.S. Bureau of Reclamation, Denver, Colorado. Report No. REC-ERC-84-23.
  4. Sartoris, J. J., LaBounty, J. F. & Newkirk, H. D. (1977) Historical, Physical and Chemical Limnology of Twin Lakes, Colorado. U.S. Bureau of Reclamation, Denver, Colorado. Report No. REC-ERC-77-13.
  5. Gregg, R. E. (1976) Ecology of Mysis relicta in Twin Lakes, Colorado. U.S. Bureau of Reclamation, Denver, Colorado. Report No. REC-ERC-76-14.
  6. Lieberman, D. M. (1983) Common Plankton of Twin Lakes, Colorado. U.S. Bureau of Reclamation, Denver, Colorado. Report No. REC-ERC-82-21.
  7. LaBounty, J. F., Campbell, S. G. & Sartoris, J. J. (1985) Primary Productivity (14C) at Twin Lakes, Colorado: 1973-1981 Study Results. U.S. Bureau of Reclamation, Denver, Colorado. Report No. REC-ERC-85-8.
  8. LaBounty, J. F., Crysdale, R. A. & Eller, D. W (1976) Dive Studies at Twin Lakes, Colorado 1974-1975. U.S. Bureau of Reclamation, Denver, Colorado. Report No. REC-ERC-76-15.
  9. Sartoris, J. J. Personal communication.