A Little Bit More
It’s important to point out that just because a pond or lake is frozen over doesn’t mean there WILL be a winterkill, however it can happen if conditions meet certain criteria. Some of the factors that influence winter kill are the depth of the body of water, the amount of vegetation present, whether there is any inflow of water from other sources, the length of the ice cover, and the snow cover on the ice.
Winterkill Criteria
Winter Severity
The thickness of ice (the thicker it is, the less light penetrates) is a major factor and the amount of snow cover (4 inches of wet snow can totally eliminate sunlight) are two major factors in winterkill. Once much or all of the sunlight is eliminated, plants can no longer produce oxygen.
Water Volume
The greater the volume of water, the less likelihood that oxygen levels will drop to lethal levels.
Plant Decomposition
Lakes and ponds that have little plant growth will have little decomposition to rob the water of oxygen. Those lakes and ponds with a great deal of plant growth, especially if little or no sunlight reaches these plants for an extended period, will experience a much greater likelihood of oxygen depletion.
Animal Biomass
It stands to reason that in bodies of water with a great deal of animal life, there will be a greater demand for oxygen during the winter months and therefore a greater chance of oxygen depletion.
Although this sounds as though wintertime is fraught with many winterkills, it’s surprisingly uncommon. Of course, when it does occur, it can be quite upsetting for those living nearby.
Activities
Science – Making Oxygen!
Objectives: Direct observation of oxygen production
Materials: Aquarium plant, quart jar, water
There are all kinds of demonstrations in science; some work well, some work so-so, and some are really impressive. I think this particular one is especially impressive and especially important for students to see. And one of the nicest parts about this is that it is so simple to do, it requires no special knowledge or skill.
- Go to a local pet store and tell them you need a small piece of a vigorous, floating water plant (Cabomba (Fanwort) or Anachris (Elodea) are two good ones) for an experiment. Bring your plant home and place in a clear quart jar with tap water.
- Place your jar in a warm and sunny location (south-facing windowsill will work best)
- Keep an eye on your mini-aquarium and on a sunny day with the sun hitting your mini-aquarium, you should be able to see tiny bubbles rising from the plant. These bubbles are oxygen bubbles being released from the plant as it photosynthesizes.
We’ve all heard about photosynthesis but few of us have seen it. I think once the students see this demonstration, photosynthesis won’t just be something they learned about, because they’ve actually seen it happening!
Key Concepts
Behavior and Regulation, Environmental Issues
Questions
Do you have a question for a naturalist? Go ahead and ask!
It's easy -- just fill out this form, submit your question and you'll receive an answer shortly.