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Turbidity
(Adapted from The Streamwatch Manual – 3rd Edition)
Definition
Turbidity is a measure of the cloudiness or muddiness of water. The greater the amount of total suspended solids in the water, the higher the turbidity results. Turbidity is measured in Nephelometric Turbidity Units (NTU).
Why test turbidity?
High turbidity can reduce light penetration and smother organisms living in aquatic habitats. If light penetration is reduced significantly, plant growth may decrease, impacting on the organisms that are dependent on the plants for food or shelter. This can result in a reduced rate of photosynthesis by plants and a lesser quantity of oxygen being released into the water.
Very high levels of turbidity for a short period of time may not be significant however long-term high turbidity can reduce biodiversity. Suspended solids can suffocate aquatic organisms (by clogging or damaging gills), prevent proper egg or larval development and interfere with feeding activities.
Causes of turbidity can be soil washed off the surrounding land during heavy rainfall or floods, bank erosion, sediment from building site developments and erosion due to land clearing.
Equipment
- Jackson turbidity tube
- Sample bottle
Method
- Collect enough creek water to fill the turbidity tube in a large sample bottle.
- Find a well-shaded area and place the turbidity tube upright on the ground.
- Shake the sample bottle to mix the sample.
- Gradually pour the water into the turbidity tube until the three lines at the bottom of the tube are no longer clear.
- The turbidity is the number below the water level.
- Discard the sample water back into the creek.
- Record the result on the recording sheet.
Updated: 04 Jan 2012