The earliest recordings of measuring the clarity of water was by the
German naturalist Adelbert von Chamisso during a Russian expedition in
1815–1818. The Secchi disk was invented in 1865 by Pietro Angelo Secchi
who described the method of lowering a white disk into the water until
it disappeared from sight. A citizen science program using Secchi disks
has been set up by Dr Richard Kirby of Plymouth University.
The Secchi disk is a 30cm white round disk. We made ours out of plastic
using the laser cutter in the tech department of my school: Rednock
School. It is attached to a weight and tape measure.
We drop the Secchi disk into the water and if everything goes
accordingly, it will go straight down until it has disappeared. This is
called the Secchi depth and shows the clarity (transparency) of the
water and can be used to suggest the amount of plankton in the sea
surrounding the area of the Secchi disk reading.
I’ve done two readings so far, one in Dundas Harbour and one in the
middle of the ice in Admiralty Inlet.
Dundas Harbour has lots of silt in its waters as many streams and a
glacier run into it. Well, the glacier has actually receded from the
water line, but as it is a bay, it is expected to be more opaque. That
first reading we got 6.9m. We use an app to record the readings and sea
temperature and any photographs of the area. The second reading was done
in the ice and also a relatively large channel so the waters were
constantly moving. That reading was 11m which suggested that water was a
lot clearer.
