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.