Tell Me Why?

When ice covers a pond or lake, it prevents oxygen exchange at the water surface with the atmosphere. However, this is not a problem where oxygen availability is concern as long as light shines through (penetrates) the ice to aquatic plants in the water. Aquatic plants provide oxygen through photosynthesis that is dissolved into the water that fish needs to survive.

If a heavy amount of snow accumulates on the ice, the amount of light penetrating through the ice will be reduced. This will result in less light reaching aquatic plants below the ice which is needed to carry out photosynthesis thus, causing the plant to die and be broken down by bacteria. These bacteria (called aerobic bacteria) will then use up the oxygen and cause a drastic drop in dissolved Oxygen in the water. When this winter oxygen depletion occurs, marine life such as fish that depend on oxygen will die because oxygen concentrations become too low for the fish to survive. That is, the demand for oxygen exceeds the supply. As fish and other marine life die, their bodies decompose and use up even more oxygen, and the depletion of oxygen gets even worse. This is called Winterkill. Winterkill occurs during especially long, harsh winters. Drought also can cause a similar fate by reducing the volume of water in the lake. This means with the less water content present, the less there will be an oxygen rich environment to support life.

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Labels: Animals, Biology, Science