It is easy to tell the time of year in a pond. Spring is the season of birth. Plants bloom. Eggs hatch. Turtles and frogs wriggle out from the shallow bottom after a long winter's nap. The water's surface ripples with aquatic insect larvae chasing each other. Male red-winged blackbirds arrive to stake their claims to the cattails. Tiny spring peepers twang for mates all night long. They only become silent when raccoons appear at the water's edge, their yellow eyes glowing in the dark.
By summer, some of the residents of the pond have started to move out. Salamanders and frogs which breathed with gills in the spring have grown into air-breathing adults. Mosquito larvae started life hanging out at the surface of the pond. Now their new wings carry them away from the water. The males will drink plant nectar. The females will drink blood and only return to the pond to lay their eggs.
Water striders tiptoe across the calm water. Turtles climb on top of each other to gain the sunniest spot on a floating log. A moose stands knee-deep in water, munching on pondweeds and water lilies. A green blanket of algae coats the surface of the pond. Most of the oxygen in the water is provided by the plants, a leftover of their making energy from the sun. Fish like large-mouth bass, perch, and brown bullhead use the oxygen by pumping water over their gills. The bass may grow to be as much as two feet long. Frogs, other fish, and even baby muskrats may become part of its food chain. The brown bullhead patrols the bottom of the pond in search of food. It is aided by its chin "whiskers"--barbels--that feel and taste whatever is on the bottom.
The crisp fall air chills the pond. Summer's birds are replaced by migrating geese and ducks. Small mammals feed hungrily on berries to build up fat for the cold season ahead. Many animals will not see the winter. They lay their eggs and die.
Gradually ice creeps out from the shore until one day the whole pond turns to glass. The frogs and turtles have retreated into the mud. Beavers and muskrats spend the stormiest days in their lodges. Cold-blooded fish aren't bothered by the winter. They just move more slowly, waiting for the spring to awaken the pond world.
Pond in a classroom
Place an inch of mud and then an inch of gravel at the bottom of an aquarium. Add rooted and floating pond plants and a few decayed leaves. Place in a window out of direct sunlight. Allow pond water to sit in an open container for a day or two and then gradually add to aquarium through a strainer to avoid disturbing plants or gravel. Collect 2 or 3 water insects, tadpoles, crayfish or snails with a homemade dip net: tape a 6-inch strainer to a broom handle.