LaMotte SECCHI DISK 1062 - Manual (Page 2)

SECCHI DISK
CODE 1062
The Secchi Disk is a white circular plastic plate, 20 cm in diameter that is
used to determine the turbidity or degree of visibility in natural water. The
Secchi Disk provides a very simple means of making transparency
determinations in natural waters. A measured line is attached to the
center of the disk by means of a special fitting that stabilizes the disk so
that it will be parallel to the water’s surface. Best results are obtained in
the shadow of a boat or dock. The best readings are usually obtained after
early morning and before late afternoon.
1.
Lower Secchi Disk (1062) into water until it just disappears. Read
depth from calibrated line.
2. Raise Secchi Disk until it just appears. Read depth from calibrated
line.
3. Add readings from Steps 1 and 2. Divide by 2. Record as Secchi Disk
Transparency.
Water that is clear has a high transparency. Transparency usually decreases
in the summer when plankton, silt and organic matter are more likely to
be prevalent. The most transparent lakes are usually seepage lakes since
the water is filtered before entering the lake, reducing silt bearing
influents. Drainage lakes carry more silt and therefore are less transparent.
For example, a drainage lake may be in a class of 1.0 to 1.4 m but a seepage
lake in the same area may give readings of 3.0 to 4.0 m. A high reading in
the class of 19 to 21m would indicate extreme clarity.
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2/07
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