Dr. Ray L. Winstead
Professor of Biology, Indiana University of Pennsylvania

Pond Ecology


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.

PHYSICAL CONDITIONS

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.

BIOLOGICAL CONDITIONS

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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Dr. Ray L. Winstead
Direct e-mail Link: RWinstea@iup.edu