Useful Links

Turbidity Gauge

The turbidity gauge is used to determine light penetration into water. This shows how clear the water is.

Lower the gauge into the water and measure how deep it gets before each segment is no longer visible. This indicates the depth to which light can penetrate. The rule of thumb is that plants can photosynthesise at depths 10 times greater than that at which the spots are no longer visible. Light allows photosynthesis to occur and oxygen to be produced.

Light penetration is affected by algae, suspended solids and dissolved nutrients.

(Note: If you want to use it more than once, encapsulate it or print it on waterproof plastic)

light meter

Secchi Disc

The original idea was invented by an Italian Admiral who lowered a dinner plate over the side of his ship to determine how clear the water was. To help visibility the plate was coloured with black and white quadrants.

This can be used in deeper water. Here the rule of thumb is that plants can still photosynthesise up to 3 times the distance measured before the disk becomes hidden by turbid water.

Secchi Disc

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