I think it is time of the year to discuss some pond and turtle care. Turtles in proper conditions do better outside. Temperate species of turtles do better with a period of hibernation. For northern animals, seasonal change is a part of natural way of life. Part of this discussion will revolve around the physical parameters of water. We all think water is just water but water responds to seasonal changes as do the animals that live in it.
WHAT HAPPENS TO WATER AS THE SEASONS CHANGE
We will start with fall season. As fall arrives and temperatures decline, water gets heavier, meaning more dense. This change of temperature at the surface causes the surface water to cool and results in surface water sinking to the bottom. The change is called the fall turnover. Cool water falls and warmer water rises to the surface. Once the water temperature hits 40 degrees from top to bottom, the process is complete. 40 degree water is at its densest and therefore at the bottom of the pond. As the water cool further toward 32 degrees, however, it rises to the surface. Once the air temperature hits 32 degrees the freezing process will begin at the surface. Meanwhile the warmer 40 degree water stays at the bottom keeping the pond open and habitable. This physical change of water is why life exists on Earth.
SPRING AND SUMMER MANAGEMENT
In the spring we have another turnover. As the water heats up a complete turnover happens again when the temperature hits 40 degrees. Every avid fisherman knows about thermoclines caused by water density changes and spring and fall turnover. In the summer the surface water gets very heated and often too hot for aquatic animals. The water density changes keep cooler water under the surface and animals will congregate to their preferred temperatures. This is called thermoregulation and all animals that can move use this physical characteristic of water to maintain health. During very, very hot weather a lot of water turnover can actually kill animals, especially amphibians and fish, so it is best not to aerate when temperatures are over 80 to 85. Aerate in the evening when temperatures go below 80 during these times of stress.
The aquatic turtle depends on this physical change in the water to survive in the winter. Without this change, fish, aquatic turtles and amphibians as we know them today would not exist.
KEEPING OXYGEN IN THE WATER DURING FREEZE UP
Turtles require oxygen in the water during the winter to survive. Once the pond freezes over for a period of time the oxygen level will decrease. The speed of the loss of oxygen in the water column depends on the amount of organic material in the pond. Organics cause an oxygen demand and that is why it is important to clean the pond in September to keep as much organic material from decomposing within the pond as possible. In order to keep the pond from going anaerobic we need to keep the pond open to some extent to allow oxygen to penetrate the water. For starters you need a pond heater to keep some of the area open and allow for some oxygen exchange.
When running a fountain or bubbler during substantial cold spells where the daytime temperature doesn’t get above 40 and the temperature dips under 32 degrees can cause supercooling and the pond can freeze all the way to the bottom. The shallower the pond the faster this happens.
A SIMPLE FACT TO REMEMBER
Do not run your fountain or bubbler when the temperature is below 40 degrees. My suggestion: turn on the fountain and/or bubbler when air temperatures are 40 and above and turn off the water flow when air temperature creep below 40. This increases oxygenation in the pond and protects your water column temperature. Increases in oxygen from top to bottom substantially improves the environment for your fish, turtles and amphibians.
A FINAL WARNING
If air temperature stays below 32 throughout the day for days at a time this is when you run the chance of a total freeze-up, especially in shallow ponds of 2 ft. or less. Running the bubbler or fountain during these cold spells turns over the warmer water from the bottom. This supercools the water and causes the pond to freeze to the bottom very quickly. In short, this spells is a disaster. Your heater becomes a life saver at this point in the winter. Do not aerate from the bottom at that time. In Pittsburgh we have been lucky the past few years in that we have not experienced any prolonged cold spells, but these extreme weather patterns will eventually catch up to us. One final recap: when the air temperature hits 40 degrees or above, use your fountain or bubbler to turn water over and reoxygenate the water to saturation. When the temperature dips below that magical 40-degree temp, turn off the bubbler and let nature sustain the life in your pond. Your pond animals will be very happy you did.