Secchi Disk

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Secchi disk

[′sek·ē ‚disk]
An opaque white disk used to measure the transparency or clarity of seawater by lowering the disk into the water horizontally and noting the greatest depth at which it can be visually detected.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Secchi Disk


an instrument for measuring water transparency in a body of water. A white disk 30 cm in diameter, it is held horizontally and lowered into the water on a rope until it is no longer visible. The depth, in meters, at which it ceases to be visible is taken as a measure of the water transparency. The disk is named after A. Secchi, who measured the transparency of sea water by this method in 1865.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
However, during the whole sampling period the Secchi disc depth measured was high, indicating that the euphotic zone always reached the sediment, favoring the germination of seeds in the diaspore bank.
Values for water temperature, dissolved oxygen, turbidity, pH, nitrite, nitrate, total nitrogen, total dissolved phosphorus, orthophosphate and total phosphorus, Secchi disc, photic zone, light attenuation coefficient (K) (m) values in September 2007, December 2007, March 2008 and June 2008 in the Carpina reservoir, northeastern Brazil.
Secchi disc transparency was the highest at station 1 with a mean value of 1.62[+ o -]0.32m obtained in March 2002.
Secchi disc transparency fluctuated between 73 and 157 cm.
A recent study also showed that the main basin of the reservoir had greater chl a concentrations (16 [micro]g [L.sup.-1]) and shallower Secchi disc readings (1.1 m [3.6 ft]) than the eutrophic criteria developed for natural lakes during the growing season (Wang et al., 1999).
At the rate of sedimentation established by current land use, both chl a concentrations and Secchi disc depths were projected to change considerably over the next century (Figure 3).
The parameters monitored were temperature, conductivity, settleable solids, flow volume, and turbidity (as measured by Secchi disc) (Table 1).
1993 1994 1995 1996 Temperature [degrees]C 10.9-16.0 9.6-10.6 8.6-12.2 14.1 Dissolved oxygen -- -- -- -- pH -- -- -- -- Secchi disc (cm) 5-20 -- -- 15 Settleable solids (mg/l) 5-25 10-20 <10 3 Conductivity ([micro]ohms) 185-190 249-255 177-184 228 TDS (Total dissolved solids) -- -- -- -- Flow (cfs) (Apr.-Sep.
Salinity (refractometer) and transparency (Secchi disc) were recorded daily; temperature and dissolved oxygen (YSI model 58) were recorded daily at 0600 and 1700 hours.
Secchi depth was estimated with a standard Secchi disc of 20 cm diameter.pH was measured in situ by a portable digital pH meter (Jenway 3200).Temperature was determined with a digital oxygen meter (Hanna 9024).
Transparency was determined by extinction method using the secchi disc by measuring the mean of the depths at which the secchi disc disappears and at which it reappears, dissolved oxygen was determined by Azide modification of the Winkler method, chemical oxygen demand was measured using the dichromate reaction method (Hach 2003), carbon dioxide and alkalinity were determined by titration (APHA 1995).