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Durand, Loyal, Jr. (ed.) / Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume XXXI (1938)

Whitney, Lester V.
Microstratification of inland lakes,   pp. 155-173 ff. PDF (5.7 MB)

Page 155

 From the Limnological Laboratory of the Wisconsin Geological and Natural
History Survey. Notes and reports No. 68. 
 It has been known for a long time that inland lakes of sufficient depth
undergo a large scale thermal stratification in summer and winter. In summer,
a temperate lake stratifies into an epilimnion, a thermocline and a hypolimnion.
The epilimion consists of the upper water which is kept in active circulation
by the wind and which has practically a uniform temperature throughout. Immediately
below this stratum is the thermocline, which is characterized by a rapid
decrease in temperature. The rate of temperature change is sometimes as much
as 50 C. per meter or more. Below the thermocline is a body of relatively
more stagnant water known as the hypolimnion in which the temperature declines
gradually toward the bottom. These three strata usually show marked chemical
and biological differences. 
 In addition to this general thermal stratification of the water, there is
also a microstratification in the thermocline and hypolimnion. This microstratification
was discovered by means of the transparency meter shown in Figure 1. This
apparatus shows the relative transparency of the water at different depths;
readings were taken in 10 Wisconsin lakes in 1936 and this report is based
on the results obtained in these studies. 
 The transparency meter is similar to that used by Hans rettersson' in Gullman
Fjord in 1933 and 1934. Pettersson also measured the variation of density
with depth and obtained curves similar to those for temperature and density
of inland lakes. He took readings at much greater depths than is possible
on small inland lakes such as those in Wisconsin; readings are indicated
on his graphs about every meter where the transpar 
 * This investigation was supported by a grant from the Brittingham Trust
1 H. Pettersson. Jour. du Cons. 10 (1): 48. 1935. Also Rap. et Proc-Verb.
d. Reunion5 
101: 3-7. 1936. 

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