Measuring in the Field with the Secchi Disk
If you have a bridge or a boat to access a way into your body of water, build a Secchi disk and measure the depth of your body of water. This is a measure of how deep light can travel in the water or, on the other hand, the turbidity of the water.
1 Choose a testing site where the water is at least a few meters deep. It is preferable to use the shady side of a boat, bridge, or dock.
2 Put on protective gloves.
3 Gently lower the disk into the water until it is just no longer visible, and record its depth.
4 Now slowly raise the disk until it reappears. Record this depth.
5 Average the two depths. This is the "Secchi depth," or the depth to which light can penetrate the water.
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Steps in Building a Secchi Disk
1 Paint the round piece of wood or plastic white.
2 When dry, paint a big X on the top and then paint alternating quadrants black.
3 Make a hole through the center of the circle using the drill or knife. The hole should be about the size of the diameter of the tubing.
4 Place the tubing into the hole and glue it into place.
5 Secure the weight to one end of the long rope.
6 Run the rope through the tubing so that the weight is hanging from the bottom of the disk.
7 Mark 50-cm sections of the rope using a permanent marker. |
