UTILIZATION OF SOLAR ENEROY BY AQUATIC ORGANISMS 



29 



meters. Althoii.uh there are a few inland 

 lakes whieli are as clear as typical coastal 

 waters, the majority of them are more tur- 

 bid.* In Midjie Lake, for example, the il- 

 himination has been reduced to 1 per cent 

 * A recent measurement in Crater Lake, Oregon, 

 (Hasler 1938) yielded a depth of 40 meters for the 

 visibility of the Seeehi disc. The clearest lake 

 which had been investigated previous to this obser- 

 vation was Crystal Lake, Wisconsin, in which the 

 Secchi disc was found to disappear at about 15 

 meters. The transparency of Crnter I^ake, there- 



of its surface value at 8 meters. The ex- 

 treme range of possible transparency in 

 natural waters is thus very great. 



In the various natural waters we find 

 tliat the relative rates of absorption of dif- 

 ferent parts of the spectrum are not the 

 same as those characterizing distiUcd water. 

 Tliis situation is brought about by the fact 

 that both the suspended and the dissolved 



fore, greatly exceeds that of any other lake in 

 which measurements have been made. 



PERCENTAGE OF SURFACE LIGHT 



Fig. 



-IIOO 



Comparison of the rates of penetration of the yellow-green component of daylight into nat- 

 ural waters (Photometer sensitive to wave lengths 500d-6000A). Curves show the relation between 

 depth and illumination expressed as a percentage of the light at the surface. The curves represent 

 the average value of the extinction coefficient for each series and no "surface loss" is included. 



