Transparency

Why are we concerned?Five volunteers stand on the banks of a forested stream and use transparency tubes to assess water clarity.

  • The transparency of water describes the depth to which light can penetrate the water. An increase in turbidity (suspended or “free-floating” solids in the water) decreases the transparency of the water.
  • The transmission of light into a body of water is extremely important since the sun is the primary source of energy for life in the stream.
  • Tracking water transparency, like monitoring your blood pressure on a regular basis, tells us about the general health of a stream.

 

The background science

Free-floating particles of soil, algae, and other organic and inorganic material can lower the transparency of water in a stream. Although small-- particles range in size from microscopic to about the thickness of a pencil lead-- their presence greatly impacts stream health. More free-floating particles result in greater turbidity and decreased transparency, which makes it difficult for sunlight to penetrate the water. Without enough sunlight, photosynthesis cannot occur, ultimately hindering the growth of aquatic plants and the production of dissolved oxygen. The water also becomes warmer because suspended particles absorb heat.

These suspended particles also interfere with the ability of fish to see and capture their prey. Sediment deposited on stream bottoms can smother fish eggs and clog the spaces between rocks where insects like to live, which in turn can lead to fewer fish that depend on insects as food. Finally, sediment may carry pollutants such as phosphorous and petroleum products. These pollutants degrade the quality of flowing water as well as downstream lakes or reservoirs.

Sources of turbidity include:

  • erosion from fields and construction sites
  • urban runoff from rainstorms and melting snow
  • eroding stream banks
  • large number of bottom feeders (such as carp) which stir up bottom sediments
  • excessive algal growth

 

We don’t directly measure how many suspended particles are in the water. Instead, we measure the transparency, which takes into account both the color of the water and the presence of suspended particles.

All streams have background turbidity, which is the base level that fish and aquatic life have adapted to over time. What causes problems in any stream or river are unusual concentrations—specifically increases—of suspended particles and the length of time the water stays abnormally turbid. The longer the water remains at unusually high values, the greater effect it has on fish and other aquatic life. Fish in particular become very stressed in waters that remain highly turbid for a long time. Signs of stress include increased respiration rate, reduced growth and feeding rates, delayed hatching and in severe cases, death. Fish eggs are ten times more sensitive to turbidity than adult fish.

 

lined paper More information is available in the fact sheet "Transparency:  A Water Clarity Measure" Links to an external site..

 

Think you've got it?

Click "Next" to learn about Dissolved Oxygen. We'll check your transparency and dissolved oxygen knowledge together in the next quiz.