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By mid-April, the greatest show on earth will have begun as the earth warms. Bird migrations are in full swing, the winter sleepers are awake and nature's life cycle has begun again.
Winter has finally lost its grip in the mountains of Northern Pennsylvania and it appears spring is here to stay. We could still see snow flurries, but they won't last long on the ground. Although ice can form along the edges of ponds, the thawing process has been complete since the end of February.
The process that a pond goes through as it thaws out in the spring is amazing. As the sun's rays become stronger the snow melts, the ice remains on the ponds. The temperature becomes warmer, and the ice starts to melt along the shoreline and then, the shallow parts of the pond. This is because the earth collects and holds the heat better than the water, and this warmer earth is nearer the surface, with less water to heat.
Sometimes a pond's ice will melt quickly, causing the pond to open in days. However, there are times when the ice is melting and we have cold weather, causing the pond to refreeze. This new ice is a thin crust and quickly disappears as the temperatures rise.
A strange occurrence could happen after the ice finally leaves the pond -- the water in the pond turns upside down. This is not something that can be seen because it is a very slow process. The spring turnover can only be observed by delicate instruments.
The turnover is the most important event that takes place in any pond or lake throughout the year. If it were not for this spring turnover, the living animals of the pond might never awaken from their winter's sleep.
Although water is lighter when it becomes solid, water from melted ice is heavier than the ordinary cold water at the bottom of the pond. As a result, the heavier water from the melted ice settles toward the bottom of the pond. When this heavier water settles, the cold water from the bottom of the pond tends to rise towards the surface, which is the cause of the spring turnover.
The melting ice immediately begins to take oxygen from the air, and as the water sinks towards the bottom, oxygen is carried along. During the winter, the ice covering the pond stops any oxygen from entering the water, and by the time spring comes, the pond is almost depleted of oxygen. If it were not for the new oxygen being carried to the bottom of the pond, the animals, which are hibernating in the mud of the pond's bottom, might not awaken.
The spring winds speed up this turnover by creating currents in the water and rippling and splashing the water in the air, where it can quickly take in a lot of oxygen.
One might think that the colder water sinking to the bottom of the pond would keep the animals in hibernation but it's the new supply of oxygen that awakens these animals.
As the cold-water sinks to the bottom, the sun warms the water on top, which in turn allows the water insects to become active again. The backswimmers, water striders and water beetles are some of the first active insects to appear after the ice melts. They are in search of food, such as tiny plants, animals and protozoa.
There are millions of these creatures, which in turn are eaten by water fleas and their relatives. Have you ever looked at a pond where the water appears to be off-color? Many times, water fleas are the reason for the water appearing to change to a yellowish or greenish color.
Tiny plants called desmids and diatoms are food for the strange creatures of the pond. The pond's animal life depends upon these little plants, which are so small they must be seen under a microscope.
Then one evening as the sun begins to set and the shadows lengthen over the pond, the first calls of the spring peepers can be heard. Their calling is one of the harbingers of spring and a sound that means the countryside will soon be turning green. For the next two months, the calling of the peepers will ring out across the land.
The pond water will soon be warm enough to have the turtles stirring. They pull themselves from the mud and swim to the surface. If they are lucky, they will find a log floating in the water and begin basking in the sun on the log. The old log sticks out of the water in the middle of the pond, providing a safe place to rest in the sun.
We begin to see several turtles sunning themselves on the same log. If they cannot find a log, they will sun themselves along the shore. The sunlight heats the turtles' cold blood and the turtles become warm. They will soon enjoy their first meal since last fall.
The turtles arriving earliest on the basking log are the males. After awakening, the males build the strength needed to plod around and engage in battle with other male turtles. The strongest males claim the choice spots on the paths that female turtles will travel as they move to their traditional nesting areas. This turtle spring will soon be in full swing.
Bill Bower is a retired Pennsylvania Game Commission Wildlife Officer. Read his blog and listen to his podcasts on the outdoors at www.onemaningreen.com.