Question

Transparency of water is measured by

• A. Secchi disc
• B. Salinometer
• C. Hydrometer
• D. Anemometer

Hint:

The Secchi disc is a simple and effective tool used in aquaculture ponds to monitor plankton density. A Secchi depth of 30 to 40 cm generally indicates a healthy plankton bloom.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Water transparency or clarity is an important water quality parameter in aquaculture and limnology.
It reflects the amount of suspended particles, organic matter, and plankton (turbidity) in the water, which affects how deep sunlight can penetrate to support photosynthesis.

Step 2: Detailed Explanation:
Let us review the functions of the listed water quality and environmental monitoring instruments:
- Secchi disc:
Invented by Angelo Secchi in 1865, this is a circular disc (typically 20 or 30 cm in diameter) divided into alternating black and white quadrants.
It is lowered into the water on a graduated rope until it is no longer visible from the surface.
The depth at which it disappears (the Secchi depth) is recorded.
The disc is then raised until it reappears, and this depth is also recorded.
The average of these two depths is the Secchi disk transparency, which is a standard measure of water clarity.
- Salinometer:
An instrument used to measure the salinity of water, usually by measuring its electrical conductivity.
- Hydrometer:
An instrument used to measure the specific gravity (relative density) of liquids, which can also be used to estimate salinity in marine aquaria.
- Anemometer:
An instrument used to measure wind speed and direction in meteorological stations.
Therefore, the Secchi disc is the correct tool for measuring water transparency.

Step 3: Final Answer:
The Secchi disc is used to measure water transparency.
Thus, the correct choice is (A).