Pond and stream formation
The study of inland waters – ponds, lakes and streams – is called limnology. Ponds form as a result of potholes in glacial debris. These holes fill by seepage and runoff water from the surrounding land. Meadow-stream ponds also develop where a stream widens and the speed of its current drops sharply, or as cutoffs from old stream channels. Streams originate in lakes, springs or in surface runoff, draining the land and taking up elements as they flow along. Constant adjustments and changes in flow or in erosion rates allow the stream to maintain balance and equilibrium. Streams are thus very dynamic, ranging from tumbling brooks in spring to sluggish, meandering waters come late summer and autumn.
Ponds and Streams
Four different microhabitats coexist within a relatively small area formed by a pond or stream: the surface film, the open water, the bottom and the littoral habitat.
The surface film is a habitat for air-breathing, floating animals, and those animals that have special devices for walking on the surface without breaking through, such as water striders. Some beetles, water bugs and free-floating plants are adapted to living only on the upper side of the film. The larvae of some beetles, as well as stonefly and mayfly larvae, spend much time hanging on the underside of the film.
The sandy bottom is home to sponges, snails, earthworms and insects. Muddy bottoms house crayfish, the nymphs of mayflies, dragonflies and damselflies, as well as leeches and snails.
The littoral habitat can be divided into three zones. The emergent plant zone is closest to the shore, where grasses, sedges and rushes provide shelter for frogs, birds, mammals, algae, protozoans, worms, insects, snails and small fishes.
Algae form pond scums and the green hairy growths on submerged objects. Green algae are the most abundant pond algae. They occur as single cells, as round and flattened colonies, and as filaments. Algae is the base of the pond food pyramid. During photosynthesis, algae release oxygen, increasing the amount of oxygen dissolved in the water. However, the overabundance of decaying algae may deplete the oxygen, causing “summerkill” of aquatic plants and animals.
Ponds and streams provide nesting and feeding grounds for many different fish species. Lampreys are jawless fish that look similar to eels. These primitive fish have a skeleton of cartilage, unlike most other fish, which have a skeleton of bone.
Brown Bullheads, like other catfish, have a smooth, scaleless skin, and chin whiskers, or barbels, that aid them in finding food. They feed mostly at night or in opaque waters. Black Crappies are large, carnivorous sunfish that sometimes grow to four pounds, although they are usually one to two pounds. Another member of the sunfish family, the Bluegill, grows up to eight inches, feeding on insects, crustaceans and other small animals. A similar fish is the Pumpkinseed, which has a bright red spot on each gill cover.
Other Animal life
Amphibians, such as brook salamanders, newts and frogs, live in the vegetation surrounding ponds and streams. The moist skin of an amphibian can absorb both water and oxygen. Frogs have lungs in addition to their breathable skin. Like most amphibians, frogs begin their life cycle in the water, with their long-tailed larvae known as tadpoles or pollywogs.
Dragonflies are graceful insects that hunt for smaller bugs such as black flies as they fly around the pond. Immature dragonflies, or naiads, are waterbound and do not resemble adults. They are dull green or brown, which helps conceal them among pond plants or beneath a film of mud. The naiads undergo a series of molts, getting larger, until the familiar dragonfly form appears at the final molt.
Many bird species nest along ponds or streams and feed on aquatic plants or on fish and other animals. Common Loons spend the summer on inland waters, feeding mainly on fish. You can hear their distinctive song on summer nights. The Great Blue Heron is a long-legged wader with sharp bills for feeding on aquatic animals. Ospreys have a conspicuous bend in their wings in flight, as they dive for fish. Surface-feeding ducks, such as American Black Ducks, Green-winged Teals, Northern Pintails and Mallards feed mainly on aquatic plants and may “tip up” in deep water. Yellow Warblers nest in willow thickets, coming to the pond to drink and to hunt for insects.
Not a fish can leap or an insect fall on the pond but it is thus reported in circling dimples, in lines of beauty, as it were the constant welling up of its fountain, the gentle pulsing of its life, the heaving of its breast.
- Henry David Thoreau, Walden
by Ogden Nash
Behold the duck.
It does not cluck.
A cluck it lacks.
It is specially fond
Of a puddle or pond.
When it dines or sups,
It bottoms ups.
To a Little Brook
by Eugene Field
All up and down this reedy place
Where lives the brook,
We angled for the furtive dace;
The redwing-blackbird did his best
To make us think he ‘d built his nest
Hard by the stream, when, like as not,
He’d hung it in a secret spot
Far from the brook, the telltale brook!