Secchi disk

The Secchi disk is a system developed by the Italian polymath Jesuit Father Angelo Secchi and in the 19th century and still in use today Limnological auxiliary device for the rapid and simple determination of visual depth in a body of water.

The Secchi disk is a generally circular sheet-metal disk of about 25-50 cm in diameter. It is black in four sectors and painted white. On the back below the midpoint of a weight is attached. At the top of a wire is fastened with a length in the label center. At this rope this disc is lowered into a horizontal position in the water and thus being watched until her visual disappearance. The depth of disappearance is read at the graduation of the rope and registered as a " visual depth " or " Secchi depth " zs.

This view depth is, inter alia, to estimate the depth of the trophogenic zone in a lake or in general to characterize the turbidity and coloration of a water body, in particular by planktonic organisms or by mineral opacities used. In about twice the depth of visibility often is the limit of the positive balance achieved photosynthesis ( assimilation > dissimilation ).

• Limnology
• Biological test method