Turbidity


Definition:

Turbidity is the concentration of particles small enough to stay suspended in the water column of bayous, lakes, or bays. These particles can block out the sunlight and make it harder to see through the water.

 

Why does it cause pollution?

Turbidity by itself is not a pollutant, but it tells you how much sediment and organic matter are in the water. Sediment and organic matter are types of pollutants that cause turbidity.

Sediment and organic matter can block sunlight that would normally penetrate the water column. If most of the turbidity is from sediment, then it can give water the appearance of chocolate milk.

Highly turbid waters decrease the growth of photosynthetic algae and aquatic plants. These photosynthetic organisms serve as the base of the food web. Various animals eat the algae or aquatic plants and larger animals eat the smaller animals. If photosynthetic algae are present in only small quantities, then filter feeding organisms, like caddis flies in fresh water or copepods in saltwater, don't have enough food. Likewise, some fish and other animals find food in the water by using their sense of sight. Highly turbid waters keep fish from seeing their food, and like caddis flies and copepods, they don't eat. This is why turbidity can be a problem.

However, high turbidity can also be from algae blooms in the water. The algae reproduce and grow at high rates in the upper part of the water column. This blocks sunlight from reaching the lower part of the water column where aquatic plants grow. In addition, algae blooms can lead to low oxygen conditions and fish kills.

 

How does it get into water?

Sediment and organic matter that cause turbidity can get into water anytime plants are removed from the land. When plants are removed, then the plant roots no longer hold the sediment and organic matter together as soil. When it rains, anything that is not held by plant roots can get washed away. This stuff ends up in bayous, lakes and bays. If the sediment and organic matter is small enough, then it stays suspended in the water. Suspended means that it doesn’t sink making the water harder to see through, like chocolate milk.

After a while, some of the sediment and organic matter that causes turbidity settles to the bottom of the waterbody. Then, a boat passes, more rain falls, or a storm with high winds stirs up the water and resuspends the sediment and organic matter from the bottom. This process is called resuspension.

One other thing causes turbidity – plankton. Plankton are microscopic plants (including photosynthetic algae) and animals that live in the water. Just like the sediment and organic matter, plankton can block light with their bodies. When plankton die they become part of the organic matter that is suspended in the water. Like plants, plankton grow when there are sunlight and nutrients in the water. Nutrients in the water create more plankton and higher turbidity.

 

What land uses are the source of this type of pollution in the B-T Basin?

  • Resuspension
  • Urban Runoff
  • Natural Sources
  • Agriculture
  • Flow Alteration
  • Forestry
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