WHAT IS IT?

Transparency refers to how easily light penetrates through a substance. In a lake, we can think about transparency as how far light can penetrate down into the water. The layer of water into which enough sunlight can penetrate to support plant life is known as the photic zone. The photic zone is where plants (algae and other aquatic plants) are able to photosynthesize. Below the photic zone, there is not enough sunlight for most plants to photosynthesize. This photic zone is very important to the lake ecosystem because algae and aquatic plants form the base of the food chain in a lake. Plants also provide much of the dissolved oxygen to the lake. Consequently, changes in transparency can affect the entire lake system.

Illustration courtesy of Water on the Web

Changes in transparency can also affect animal species that are visual predators. How well they can see through the water will affect their ability to find food. Again, changes in one organism’s ability to play their part in the food web can effect the entire lake ecosystem.

The illustration to the left, courtesy of Water on the Web, is of a typical lake food web. It shows how members of the lake community interact.

Help with vocabulary:

piscivorous fish =
fish that eat other fish

planktivorous fish =
fish that eat zooplankton

To learn more about fish, go to the Fish & Angler section of the Lakes Guide.

To learn more about zooplankton, go to the Aquatic Plants & Animals section of the Lakes Guide.

The ability of light to penetrate into water decreases with depth because the light is absorbed or scattered by dissolved and particulate materials in the water. Examples of these materials include dissolved organic carbon (DOC) that can make water tea-colored. Much of the DOC in a lake comes from decomposing plants within the lake itself and in surrounding wetlands. For more information about color in lakes, see the Lake Color page of the Lakes Guide. Particles (suspended solids) in the water, such as sediment and algae, both scatter and absorb the light coming down through the water column.

Resources:

Bronmark, Christer and Lars-Anders Hansson. 1998. The Biology of Lakes and Ponds. New York. Oxford University Press.

Water on the Web