Imagine you are looking at a pond. What do you see? Many would say water, plants, fish, maybe a few frogs. But there is much more to a pond ecosystem than just meets the eye. In the spring, a pond is an area teeming with life, while during the winter, everything seems to go still. So what exactly is happening just below the surface?
During the winter, it may seem like everything in a pond has been put on hold. This is partially true, as activity is slowed greatly during this season. Turtles and frogs have retreated into the cozy warmth of the mud. Insects are no longer skimming across the surface. The metabolism of organisms in the pond as well as the amount of photosynthesis that is taking place is greatly decreased during the winter. This is an important adaptation as both food and sunlight are in short supply. In areas where ice is able to form on a pond, several changes occur. Since ice is less dense than liquid water, ice will form at the top of the pond and will even provide insulation for the water underneath. Just below this icy layer, life still exists, but in a much more lulled state. The ice prevents a lot of sunlight from reaching the bottom, and with shorter daylight hours, very little photosynthesis takes place. The layer of ice also prevents normal gas exchange within a pond from occurring. Without access to the atmosphere, there will be much less dissolved oxygen. Luckily, colder water holds more oxygen, and pond animals are adapted to use much less oxygen in the winter than they would in the summer. This is what makes a winter pond seem so tranquil, as the pond organisms are trying to use as little energy as possible. Although everything is still during the winter, the pond organisms are getting ready for a season that is anything but still.
As the air temperature warms and the ice cracks and thaws the pond seems to spring to life again. During this season, the pond is open to normal gas exchange processes and the dissolved oxygen content begins to increase. The pond is also opened up to more sunlight, which leads to a cascade of life processes beginning again. The first sign of the affects of spring in the pond is that the pond will become murky. This is due to bacterial and phytoplankton blooms. Then the decomposers of the pond will begin breaking down dead matter and releasing important nutrients into the body of water. With the presence of sunlight, ammonia, and carbon dioxide now readily available, algae will begin growing. This is an important food source for herbivorous micro- and macro-organisms. Amphibians are drawn back to the water source from which they are born, and soon the calls of frogs and toads will ring out from the edges of the pond as they begin their reproduction cycle. The fish and aquatic invertebrates will also come to life after their long resting season. Spring is the season of new life and action in a pond.
Photo credit: Macroscopic Solutions
During the summer, the pond becomes calm again. Turtles bask lazily in the sun, as fish catch insects on the surface of the water. Frogs and salamanders are entering their adult stages and leaving the water, as aquatic invertebrates go through metamorphosis and sprout wings. Most of the oxygen that is now in the water is provided by the abundant plant life soaking in the sun. Insect catching birds soar across the water in search of their next meal. During hot summer days, water temperature may increase greatly. Fish will retreat to the depths of the pond in search of cooler temperatures. Amphibians rely on bushes and other plant coverage on the edge of ponds for shade from the sun. The summer provides a warm resting period for the pond after a long season of activity and reproduction.
This is a season of change, not just in the trees, but in the pond as well. It is a time of transition, where the pond ecosystem is getting ready for the still, cold winter. As the pond's temperature decreases, it will absorb more oxygen. This is a cue for the organisms in the pond to use less oxygen and energy. Fish will produce less ammonia so that it doesn't get trapped under the ice during the winter. In place of the summer birds, geese and ducks will migrate in. The berries that were produced in the end of summer will be picked clean by small mammals preparing for winter. This is a season of preparation, so that each species is able to survive a harsh winter.
A pond is constantly going through changes, as life circulates in and out of the ecosystem. Everything that lives there depends on the water. Each small change in the water means a change for every life form living there. The pond ecosystem is an exciting and fascinating example of the ebb and flow of life throughout the seasons.