Dr. Ray L. Winstead
Professor of Biology, Indiana University of
A pond is a small, shallow body of fresh, standing water in which relatively quiet
water and extensive plant growth throughout are common characteristics. The basic
difference between a pond and a lake is depth. A pond is shallow with light penetrating
to the bottom throughout the pond. A lake has a deeper area where light does not
penetrate to the bottom in sufficient intensity to support photosynthesis by plants. A
pond may be formed by Humans, be formed naturally (e.g., a cut-off from a stream), or be a
remnant of a previously existing lake.
Water Movements: Water movements in ponds are minimal because of the small areas
involved and, in many, protection from the wind by the surrounding environment.
Stagnation of the water in the bottom levels is common.
Temperature: Because of the shallow depth and large expanse of surface as compared
with volume, pond waters tend to follow the general trends of temperature of the
surrounding air. However, variation in the temperature is not as extreme as in the air.
Aquatic organisms usually have narrow ranges of tolerance for temperature, so any unusual
change in temperature in a pond will alter the community of organisms present.
Turbidity: Turbidity refers to the condition of a body of water that contains
suspended material such as clay or silt particles, small dead organisms or their parts, or
small living plants and animals. Turbidity varies greatly in different ponds depending
upon local conditions. Ponds with mucky or clay bottoms maintain, more or less
permanently, a layer of cloudy water just above the bottom. Ponds with sandy or gravel
bottoms have lower turbidity. Turbidity within a pond may change rapidly due to rains.
Light: The shallow depths of ponds usually allow enough light so that plants occupy
the entire bottom, as well as large populations of phytoplankton at all levels. Luxuriant
growths of plants in (older) ponds shade the underlying water.
Oxygen Content: Oxygen content varies according to the local conditions (e.g.,
depth, protection from the wind). Over sandy bottoms of younger ponds abundant dissolved
oxygen prevails. Water over vegetation has a moderate amount of dissolved oxygen at least
during the day. In older ponds the lowermost water has an oxygen supply during the spring
months, but during the summer the water is devoid of oxygen. Oxygen supply in the water
goes down at night. Aquatic animals have narrow ranges of tolerance for oxygen and are
very sensitive to reduced oxygen. Therefore, organic pollution, which reduces oxygen
levels because of increased bacteria activity, is especially damaging.
Plants: Well-developed pond vegetation tends to be arranged in zones more or less
parallel to the shore line. In general, these are usually the marginal zone of emergent
plants, the zone of floating plants, and the zone of submerged plants. In older and more
productive ponds, algal growths often become conspicuous.
Animals: Insects usually are the most abundant and have the greatest diversity of
species. Of the other invertebrates, the protozoa, rotifers, crustaceans, and snails are
most important. Among the vertebrates, amphibians (e.g., frogs) are considered by some as
the most important group. Fish may be reduced to minor densities (except in larger,
permanent ponds) compared to lakes. Pond animals, particularly those of temporary ponds,
are largely composed of species which may have a part of their life cycles out of water
(e.g., flying insects). Surface-film animals and those that come out to the surface for
breathing are often abundant. The diversity of pond animals is very variable and may
change greatly from year to year. Many organisms are benthic, i.e., bottom dwellers.
Succession: In general, the trend is for the pond to fill from materials washing in
from the surrounding land and eventually become a terrestrial environment. The
characteristics of a pond depend a great deal on its age.
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