LINDBERGH LAKE WATER QUALITY UPDATE
Prepared for Gail Harris, Lindbergh Lake Homeowners Association
Prepared by Ken Knudson, KNK Aquatic Ecology
August 26, 2003
With the assistance of Jeff Wolf, water samples were collected at three
stations on Lindbergh Lake, as well as on the Swan River above and below the
lake, on August 19, 2002. The attached tables summarize the results of the
analyses of these samples as well as the results from samples collected during
six other Augusts between 1989 and 1997. For further explanation of the
parameters discussed below, as well as the locations of the sampling stations,
please refer to the August 1994 Lindbergh Lake Report.
Table 1 shows water temperatures at 10-foot depth intervals at the three
stations on Lindbergh Lake. Generally speaking, the lake’s water temperatures
were somewhat cooler at all depths from 1993-2002 compared to 1989-1992.
For example, the surface water temperature at Station 2 during August 1989
(21.3  C or 70.3 F) was nearly 4 C or 7 F warmer compared to August 2002
(17.4  C or 63.3 F). Even in the deepest portions of the lake, temperatures were
roughly 2 C or 3.5 F warmer during 1989 compared to 1997 or 2002. The cause
of this apparent cooling trend is difficult to pinpoint, since lake water
temperatures are influenced by a myriad of factors, including air temperature, the
timing and amount of runoff, solar radiation, amount of spring and summer
precipitation and the frequency of wind and cloud cover. However, all of these
potential influences on Lindbergh Lake’s long-term temperature regime are more
likely global in scale rather than being related to any activities in the lake’s
watershed.
Dissolved oxygen concentrations at 10-foot depth intervals are shown on
Table 2. Trout growth rates become marginal when dissolved oxygen
concentrations drop below 7.0 milligrams per liter (mg/l). As can be seen on
Table 2, the depth at which trout growth was marginal in Lindbergh Lake ranged
from 110 feet in 1991 and 1995 to only 80 feet in 2002. The concentration of
dissolved oxygen in mountain lakes is influenced primarily by oxygen production
(or photosynthesis) by algae and other aquatic plants during daylight hours, and
oxygen uptake (or respiration) by the algae, bacteria, fish and other lake
organisms. The dissolved oxygen concentration that would be present in a lake
at a given elevation and temperature without the presence of any plant or animal
activity is called the saturation concentration. The values for the percentage
saturation of dissolved oxygen on Table 3 were derived by dividing the dissolved
oxygen concentrations in Table 1 by the saturation concentrations at the
elevation of Lindbergh Lake and the temperatures in Table 2. Saturation values
greater than 100% indicate oxygen production, while values less than 100%
indicate higher levels of respiration compared to production. Oxygen production
rates were fairly constant in the upper 30 feet of the lake throughout the period
from 1989-2002. However, moderate oxygen deficits, as indicated by dissolved
oxygen saturation values less than 70%, were present at depths as shallow as
60 feet for the first time in 2002.
Throughout the study period, concentrations of nutrients that stimulate the
growth of algae were very low at all the sampling stations. In fact, concentrations
of ortho phosphorus and nitrate nitrogen, the two most bioavailable forms of
aquatic nutrients, were not even detected in nearly three-quarters of the
laboratory analyses conducted on samples from the lake’s surface and from the
Swan River above and below the lake (Table 4). As is typical of mountain lakes
during summer, the highest concentrations of nutrients were found at the bottom
of Lindbergh Lake during all the years. Even at this deep-water station, however,
the highest total phosphorus concentration (0.029 mg/l) and the highest nitrate
nitrogen concentration (0.04 mg/l) were still less than half the levels that are
necessary to cause nuisance densities or “blooms” of algae. Such blooms are
the greatest threat to the crystal-clear water clarity of Lindbergh Lake.
Based on the results of the parameters analyzed during this study, the
overall water quality of Lindbergh Lake remained very good during the period
from 1989 through 2003. However, the increased incidence of dissolved oxygen
concentrations less than 7.0 mg/l and dissolved oxygen saturation values less
2
than 70% during recent years, suggest that a slight deterioration of the lake’s
water quality could be occurring. It would be prudent to sample Lindbergh Lake
again in August 2004 or 2005 to help determine if this deterioration is stabilizing
or worsening.
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August 26, 2003
Invoice No. 14.01
Gail Harris
Lindbergh Lake Homeowners Association
FIELD WORK AND REPORT PREPARATION FOR LINDBERGH LAKE
WATER QUALITY STUDY.
LABOR
K. Knudson - Travel
Field
Office
5.0 hr @ $55/hr
6.0 hr @ $55/hr
8.0 hr @ $55/hr
Subtotal Labor
$275.00
330.00
440.00
$1,045.00
OTHER DIRECT COSTS
Nutrient Analyses
(Energy Labs)
Mileage
258 mi. @ $0.365/mile
Subtotal ODC
$300.00
94.17
$394.17
Total Due
$1,439.17
________________________________________________________________
Terms: Net 30 days
Finance Charge: 2.5% per month on past due account (30% APR)
PLEASE MAKE CHECK PAYABLE TO:
KNK AQUATIC
ECOLOGY
Taxpayer ID 81-0524928
Thank you.
________________________________________________________________
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