Factors that Affect Productivity in Wintering Lakes: An Analysis of Lake Zones and Snow Depth
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Transcript of Factors that Affect Productivity in Wintering Lakes: An Analysis of Lake Zones and Snow Depth
Factors that Affect Productivity in Wintering Lakes: An Analysis of Lake Zones and Snow Depth
Kristen KernanWinter Ecology- Spring 2012
Relevant Terminology
• Productivity- Amount of photosynthesis occurring due to phytoplankton
• Limnetic Zone- Open surface water in a lake, well-lit, and can contain many aquatic organisms
• Littoral Zone- near shore area that can maintain aquatic plants
• Chlorophyll- a pigment present in phytoplankton used to absorb light for photosynthesis
Why Should I Care?• Phytoplankton remain active
during the winter and adjust to changing light conditions (Marchand, 1987)
• Lake productivity is related to nutrient content and affects the number of species found in a lake
• Light is a limiting factor in wintering lakes and snow coverage can make light penetration more difficult
Background
• Evergreen Lake in Evergreen, Colorado• Within the Bear Creak watershed and created
by damming Bear Creek in 1927• Elevation= 2,200.656 meters• Size= .1699 km^2
Bear Creek Watershed
Background (cont.)
• Heavily used for recreational purposes: ice skating, ice fishing, resides on the outskirts of a golf course
• Completely ice covered• Snow covered on ~90% of the lake except for
the area cleared for ice skating
Research Question and Hypotheses
• Question: Is the limnetic zone or the littoral zone more productive?– If the limnetic zone is less productive then levels
of chlorophyll will be higher in the littoral zone• Question: How is productivity affected by
snow coverage?– If productivity is affected by snow coverage then
sites with less snow will have higher levels of chlorophyll
Methods: Sample Collection• Samples were collected using a 2-liter Van Dorn and then stored in a cooler
to limit light exposure and temperature change– Limnetic
• Central Location• Depth= 4.1 meters• Ice Thickness=30 cm• Snow Depth= 35 cm• Samples were taken at 1meter and 3 meter depths
– Littoral 1• Near-shore site• Depth=1.5 meters• Ice thickness= 15 cm• Snow Depth= .5cm• Sample taken at 1 meter depth
– Littoral 2• Depth=1.5 meters• Ice thickness= 25 cm• Snow Depth= 35 cm• Sample taken at 1 meter depth
Methods: Filtration, Extraction, and Analysis of Chlorophyll
• Samples were filtered using a glass fiber and stored in a plastic test tube and kept in a freezer until extraction
• 10 mL of ethanol was placed in each test tube • Chlorophyll was extracted at 78 degrees Celsius
(the boiling point of ethanol)• Post extraction samples were filtered once more
and then ran on a spectrophotometer at wavelengths of 665nm and 750nm.
Results: Limnetic Vs. Littoral
5.8
5.9
6.0
6.1
6.2
6.3
6.4
Limnetic: 1 meter Limnetic: 2 meter Littoral: 1 meter
Chlorophyll in micrograms/liter: Limnetic vs. Lit -toral
Chlo
roph
yll (
ug/l
)
Limnetic: 1 meter
Limnetic: 3 meters
Littoral: 1
meter
6.3 ug/l
6.0 ug/l
6.2 ug/l
• Chlorophyll was fairly uniform from Limnetic to Littoral
• Increasing lake depth at limnetic site showed a decrease in chlorophyll by .3ug/l
Results: Snow Depth Comparison
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
Litt 30cm Litt 2mm
Chlorophyll in micrograms/liter Between Sites
Chlo
roph
yll (
ug/l
)
Littoral 30cm
Littoral .05 cm
6.2 ug/l
8.2 ug/l
• Higher amounts of chlorophyll at littoral site with half centimeter of snow
Discussion
• Rejection of hypothesis that littoral zone is more productive than limnetic zone in winter lakes– Chlorophyll at both locations about equal
• Acceptance of hypothesis concerning snow depths affect on productivity– More snow coverage=less algae=less photosynthesis
• Chlorophyll levels indicate the lake is on the low side of being Mesotrophic (Carlson R.E. and J. Simpson, 1996)– Some evidence suggesting that this may be a characteristic
of a wintering lake (French et al., 2007)
Discussion (cont.)
• Bear Creek Reservoir in comparison(Clayshulte 2010):– Same watershed– Lower elevation– Eutrophic lake– February of 2010 chlorophyll 14 ug/l– Has experienced algal blooms
Conclusion
• Near shore versus open water doesn’t appear to be much of a factor concerning chlorophyll in wintering lakes
• Snow depth has a larger impact on productivity due to the availability of light
• If given the opportunity to re-do project:– Couple data with hydrolab depth analysis– Pick a known eutrophic lake– Collected more samples
Literature Cited• Carlson R.E. and J. Simpson. “A Coordinator's Guide to Volunteer
Lake Monitoring Methods.” North American Lake Management Society. (1996):96 pp. Print.
• Clayshulte, Russell. “2010 Annual Report for the Water Quality Control Commission.” Bear Creek Watershed Association (2010): 1-38. Print
• French, Todd, and Ellen Petticrew. "Chlorophyll a seasonality in four shallow eutrophic lakes (northern British Columbia, Canada) and the critical roles of internal phosphorus loading and temperature." Hydrobiologia 575 (2007): 285-299. Print.
• Marchand, Peter J. Life in the cold: an introduction to winter ecology. Hanover, NH: University Press of New England, 1987. Print.