HOW IS IT MEASURED?

Dissolved Oxygen is most easily measured using a dissolved oxygen meter (it can also be measured by adding a series of chemical reagents to a water sample). The meter has a probe that is connected to a display screen with a long cord. The probe is lowered vertically down into the lake. The probe has a very sensitive membrane which can detect changes in dissolved oxygen levels. It sends this information to the display screen.

In this picture, we can see all of the parts of the meter. In the lake scientist's right hand is the probe, the cord is wrapped the big black spool resting on his knee, and the display screen is in his left hand.

Dissolved oxygen readings are generally taken at every meter of depth. The readings are recorded on a field data sheet and can then be used to produce a dissolved oxygen profile, a graph of how oxygen levels are changing with depth. Readings are compared against other sample dates to tell whether conditions are staying the same or changing for some reason. Dissolved oxygen meters also provide measurements of water temperature.