Measurement of Transparency in Water

Transparency of the water is measured as the measure of turbidity. Turbidity of the water restricts the light penetration. It affects the primary productivity and distribution of organisms such as phytoplankton and fishes in the water column. Some organisms use their vision to find their food. They are interfered by the high turbidity.  Two types of turbidity are available in water such as organic turbidity and inorganic turbidity.

                              Organic turbidity is caused by dead organic materials (detritus), phytoplankton and zooplankton. Organic turbidity is considered as an index of primary productivity because higher the organic turbidity means higher number of photosynthetic organisms. So it increases the primary productivity. But since the photosynthetic organism tend to be retain near the surface in order grab maximum sunlight they restricts the depth which available for themselves to live.

                         Inorganic turbidity is caused by suspended clay and slit particles. It reduces the light penetration through the water column. Therefore eventually altogether both organic turbidity and inorganic turbidity decreases the light penetration and reduces the space available for the life.

                         Turbidity is measured by using two method such as sechi disk and seston weight method.

Sechi disk

                       It is a disk with 20cm diameter. It is dived into four quarts with altering black and white. The disk is lowered into the water aid in a thin rope. The depth where the white color quarts disappear is measured as the sechi depth. 

Disadvantages:

1)    It is not measured organic turbidity and inorganic turbidity separately. It gives reading of combination of organic turbidity and inorganic turbidity.

2)    Readings are user dependent because visibility changes person to person.

3)    Readings are influenced by external environmental factors such as solar intensity and waves.

4)    If it does not shrink straight, it does not give accurate readings. A weight is hanged to the bottom surface to direct the disk to shrink directly.

Seston method

                         It supports to measure organic turbidity and inorganic turbidity both in quantity and quality. The procedure is done as follows.

·        The weight of nitrocellulose paper is weighed. (w1)

·        Known volume of water is filtrated through the filter paper.

·        The filtrate is dried at 80°c in an oven for 24 hours. Then weight of fitter paper and residue is weighed. (w2)

·        Total seston weight= (w1-w2)

·        The filter paper and residue is burned in a Muffle Furnace at 450°-500°C for 12 hours.

·        Then weight of residue after burning is weighed.(w3)

·        Inorganic turbidity= w3

·        Organic turbidity= (w1-w2)-w3

Advantages:

1)    Readings are not influenced by eternal environmental factors.

2)    Organic turbidity and inorganic turbidity can be measured separately.

Disadvantages:

1)    Errors are possible due to the instruments.