Factors that Affect Productivity in Wintering Lakes: An Analysis of Lake Zones and Snow Depth Kristen Kernan Winter 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
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 6.3 ug/l • Chlorophyll was fairly uniform from Limnetic to Littoral • Increasing lake depth at limnetic site showed a decrease in chlorophyll by .3ug/l 6.2 ug/l 6.0 ug/l Littoral: 1 meter Limnetic: 1 meter Limnetic: 3 meters
Results: Snow Depth Comparison 8.2 ug/l 6.2 ug/l • Higher amounts of chlorophyll at littoral site with half centimeter of snow Littoral 30cm Littoral .05 cm
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.