Secchi disk

Productivity Trophic status Mean total P. M-g/L Mean annual chlorophyll, pg/L Oxygen concentration, as % of saturation Secchi disk depth, m... 

Berman, T., WaHine, P. D., SchneUer, A., Rotherberg, J., and Townsend, D. W. (1985). Secchi disk depth record A claim for the eastern Mediterranean. Limnol. Oceanogr. 30, 447-448. 

The depth in water to which a Secchi disk (a 20 cm diameter disk with alternating black and white quadrants) can be seen from the surface. Secchi disk depth is an easy measurement of water transparency. 

Trophic state can be measured directly via indicators of phytoplankton biomass and nutrient concentrations or indirectly by measuring water transparency (Table 1). Water transparency can be an accurate indicator of phytoplankton productivity, even though it is affected by nonbio-logical particles suspended in the water column. Secchi disk depth is the oldest, simplest, and quickest quantitative measure of water clarity. A Secchi disk is a black and white disk that is... 

Figure 4 Changes in Lake Washington water quality in relation to sewage diversion, (a) Mean (July-August) lake surface (epilimnetic) chlorophyll a concentration, (b) Mean (July-August) Secchi disk depth. The vertical lines show the range, (c) Bars = annual mean of total phosphorus in the epilimnion. Circles = mean (January-March) bio-available phosphorus (phosphate) concentrations in the epilimnion. (d) Relative amount of sewage as indicated by the capacity of the treatment plants emptying into the lake, maximum taken as 100% (reproduced by permission of American Society of Limnology and Oceanography from Nutrients and Eutrophication, 1972, pp. 172-193).

Figure 6 Mean annual primary productivity and mean monthly Secchi disk depth over time in Lake Tahoe (reproduced hy permission of Backhuys Puhhshers from The Great Lakes of the World (GLOW) Food-web, Health...

The extinction coefficient 17 may be calculated from measurements of I made by a light meter. The Secchi disk is another time-honored device for estimating light penetration in a lake. In 1865, P. A. Secchi developed this method, which was subsequently used aboard the papal yacht, S. S. L immacolata Concezione. The Secchi disk is about 20 cm in diameter, col-... 

In situ turbidity determinations using a Secchi disk are related to, but do not strictly correspond to suspended solids determinations [15]. The disk is a circular plate of about 20 cm in diameter made of sheet steel or other metal, and is painted with alternating black and white quadrants on its upper face. A rope or chain calibrated in meters is attached to the disk via an eyebolt at the center of the disk, so that the disk hangs horizontally. For a reading, the disk is lowered into the water until the black and white painted quadrants appear to be uniformly gray due to the turbidity of the water, and the depth at which this occurs is recorded. It is then lowered a few meters more and then... 

This section nses two well known equations [1-3] estimating Secchi Disk Transparency (SDT) nsing Satellite Imagery. Both of these equations are used to estimate the SDT for the given sample points. 

Predicting Water Quality by Relating Secchi-Disk Transparency and Chlorophyll a Measurements to Satelhte Imagery for Michigan Inland Lakes, August 2002. 

Historic data on Secchi disk depth in the northern Adriatic Sea in 1911 through the present, with few interruptions of data collection, provide a measure of water transparency that could be interpreted to depict surface water productivity. These data coupled with surface and bottom water dissolved oxygen content determined by Winkler titrations and nutrient loads outline the sequence of eutrophication in the northern Adriatic Sea. Similar historical data from other coastal areas around the world demonstrate a decrease in water clarity due to phytoplankton production in response to increased nutrient loads that are paralleled by declines in water column oxygen levels. 

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