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, 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 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 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): 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): Print. Marchand, Peter J. Life in the cold: an introduction to winter ecology. Hanover, NH: University Press of New England, Print.