Diurnal mixing in the water column… under ice.An investigation of the movement of organic detritus through the water column over one day in an seasonally ice covered lake in Evergreen, Colorado.

By John MotleyWinter EcologySpring of 2012

Outline of presentation:• Introduction:

• The Necessity of Movement• Stability Under the Ice• The Question

• Methods: • Site Selection and Sample Site Conditions • Sampling Process • Lab Procedures

• Results:• There is Movement!• Hypothesis for Movement

• Discussion Questions??? • Conclusion• Notes• Literature Cited

The Necessity of Movement• Redistribution of nutrients is essential for life • Movement requires energy• Energy from the sun drives all forcings• Diurnal movements of organisms coincides with

changing levels of solar radiation• But, in winter this energy is limited

Stability Under the Ice

• Formation of Ice sheet• Reduction in fluxes • Solar radiation diminished • Density and temperature stratify

lake• But life still exist and functions

through out the winter.

The Question

•Is there a diurnal movement of organisms through the water column???•To find this out I went to an ice covered reservoir.

Site Selection• Evergreen Lake in Evergreen, Colorado• Collection allowed. Safe ice conditions. Accessible. Exact site pointed out by arrow.

Sample Site Conditions

• Managed by Evergreen Parks and Recreation for fishing and boating in the summer and open to ice fishing and skating in the winter. Known as a productive lake with good fishing. • 4.5 m deep at sample location• Water clear with hints of greenish brown• Secchi Depth: 205 cm• Air temp. Max 0 degrees C, Min -11 degrees C• Ice depth 35 cm • Snow depth 30 cm• Slight breeze from NW

Sampling Process • 1 gallon samples were collected 4 time through out the day• 12 pm, 5 pm, 8 pm, 3 am.

• At 4 depths: 1 m, 2 m, 3 m, 4 m.• Samples where then filtered in the field with a 10 micron

gauged sleeve, reducing sample to 250 mL. • Ethel alcohol was used to preserve samples and keep them

from freezing• Samples were then stored in a cool and analyzed the next day.

Lab Procedures • Filtered 50 mL of each of the 16 sample. • Analyzed samples for zooplankton• Compared organic particulate in filtered samples to determine

movement through water column.

12:00 17:00 20:00 03:00

There is Movement!

• As the graph shows, there is movement of the organic particulate that was collected in the samples over the span of one day.

•But why?

Hypotheses for Movement

• Viner states that thermal stability will dictate phytoplankton's distribution through the water column as light penetration is related to density.• But this water is not completely stable, and with snow and ice

cover there is little solar radiation reaches the water. • Bengtsson declares that mixing in ice covered lakes is caused

by through-flow currents, oscillation of the ice cover and by convective heat flows from sediments or from solar radiation penetrating the ice. • I am suggesting that it may be two of Bengtsson’s theories.

• Through-flow currents and convective heat flows from solar radiation and possibly from heat flows from the sediments.

Reflections• Most likely:• Through-flow currents from near by tributaries• Adds sediment through transport

• Highest sediment levels after full day of sunshine

• Could be:• Large section cleared off for ice skating. • Distributes solar radiation unevenly across the lake

• Causes movement by heating some sections of the lake preferentially.

• Probably not:• Thermal heating from sediments• Decomposers in sediment causing releasing heat

• Mixing sediments into the water column

Discussion Question???• If through-flow is the cause of movement, how might

movement be site specific?• What role might the ice rinks play in primary production

during the winter?• Does regularly fissured ice (from ice fishing) impact lake

stratification, chemistry, or light inputs?• What impacts might the near by golf course have during the

winter?• Why does there appear to be so little productivity in Evergreen

Lake in the winter?• How might this experiment be improved?

Conclusion• This brief exploration into movement through the water

column draws new questions to explore. With better equipment and more data, a more concrete understanding of this movement under the ice is possible.

• The thermal gradients play a large role in distribution of aquatic life, but this study shows that even with substantial ice cover there is movement beneath the ice even with substantial snow cover.

• There is little literature on the biological functions that occur in winter under seasonally covered lakes and this field is exciting to explore.

Notes• Nutrient movement is a requirement for all levels of life from the circulation through ecosystems to the transfer in

and out of a single cell organism all. Our world is a closed system, where energy and nutrients are cycled from one organism to the next. But this cycling requires some type of energy or forcing to initiate movement. The sun being the initial driver. In the summer lake surfaces are exposed to both sunlight and wind provide direct energy through out the water column as well as mix the water column and redistributing nutrients. As phytoplankton rely on the sun as their energy source the move through the water column to obtain optimal light. But during the winter months light levels are lower and these processes slow if not stop completely. In turn life must adjust to this new energy limited system.

• 1. Formation of the ice sheet occurs after the fall mixing when water temperature becomes homogenous through out lake and freezing begins to occur at the lake surface. In alpine lakes this ice sheet seals the lake from the atmosphere. This causes a 2) reduction of fluxes essentially ceasing mixing by wind and 3) diminishes the solar radiation that enters the water column. In this new more stable condition 4) water density and temperature stratify the lake and keep movement of organism in the water column relatively stable. And this leads me to my question.

• In hindsight a more secluded lake could have limited some of the variables (golf course and ice rinks).• Initial experiment idea was to find out if solar and lunar radiation had any correlation to zooplankton movement

through water column over the course of one day. • Sampling process would have been facilitated by a Hydro Lab. • Samples taken at 4m depth had too much sediment in them for true analysis and as such were disregarded. • Despite being aided by Dr. Sarah Spalding, I could find no zooplankton in any of the samples taken. But I noticed a

strange trend of movement of organic material through the water column over the day with its peek coloration at 5 pm. I found this odd as it did not correlate with the time when the lake would be receiving peak solar radiation. And developed some hypothesis after exploring some other studies.

• In future tests I would like to use a Hydro lab to get exact reading on temperature, oxygen levels, pH and electrolysis. Using just the Van Dorn does give a visual interpretation of what is occurring beneath the ice but having more, and various types of data could have given me a better idea of what was inducing the movement of sediments.

• Finding so little life in this heavily fished lake seemed odd. More research should be done to understand what is sustaining its fish population.

• Another interesting study would be to see what effect the adjacent golf course has on the lakes chemistry.

References Cited • Boylen, Charles W. and Brock, Tomas D. “Bacterial

Decomposition Processes in Lake Wingra Sediments During Winter” Limnology and Oceanography , Vol. 18, No. 4 (Jul., 1973), pp. 628-634. Published by: American Society of Limnology and Oceanography. Found on Febuary 22, 2012 at http://www.jstor.org/stable/2834356

• Viner, A. B. “Thermal Stability and Phytoplankton Distribution.”Hydrobiologia,Volume 125, Number 1, 47-69, 1996. Kluwer Academic Publishers. Found on Feb 22, 2012 at http://www.springerlink.com/content/0018-8158/125/1/• Assisted by Sarah Spalding of the INSTAR lab.