Turbidity Information Sheet Background Turbidity is the cloudiness of water and is the result of suspended material in the water. This suspended material decreases the ability of light to pass through and this can limit plant growth.
This in turn affects the fish and invertebrate communities
which feed on and live in the plants. organisms, plant material and chemicals.
Turbidity may be caused by silt, microHowever, the most frequent causes of
turbidity in rivers and other water bodies are algae and inorganic material from soil weathering and erosion.
Effects of Turbidity High levels of turbidity have a two-fold effect on water:-
a) It loses its ability to support a large variety and number of aquatic organisms. Where there is less light penetrating the water, there will be less photosynthesis occurring and this reduces the level of oxygen in the water.
b) The water becomes warmer because any suspended material absorbs heat from the sun. This also decreases the amount of oxygen dissolved in water.
Controlling Turbidity Certain catchment management practices such as the retention of vegetation along streams, farming practices such as contouring and stubble retention and the effective treatment of effluent from sewage works can reduce turbidity levels.
Measuring Turbidity Turbidity is normally measured by an instrument called a Nephelometer.
This
instrument determines the scattering of light and is measured in standard Nephelometric Turbidity Units (NTU).
Normal levels of turbidity can vary from less
than 1 in clear pristine streams to very much greater than 200 NTU in murky rivers after flood events.
Turbidity Tube Instructions This method should be followed if using a Turbidity Tube.
Equipment Water column turbidity assessor Sample container
Method 1. Shake sample vigorously before examination. 2. Gradually pour the water sample into the water column while looking vertically down into the assessor. Hold the assessor out of direct sunlight at this stage.
3. Stop pouring at the point where the black mark on the bottom of the assessor is just visible.
4. Note the reading from the scale on the side of the assessor. 5. If the reading is above 200, dilute the sample 1: 1 with clear water. Multiply the result by 2 to give the turbidity.
If the result is still above 200, repeat the 1: 1
dilution and multiply the reading by 4.
Checklist •
Try to take turbidity readings in the same light each time.
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Add your water sample to the tube until you feel that you have the true reading. Record the reading and then add a little more sample and reread the tube.
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If the turbidity is less than 8 (water can fill the tube and the lines are still visible), either record the test as
