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In August 1938 the absorption of light was measured at various depths in the Okoboji Lakes by means of a photronic cell and a tungsten filament lamp which were mounted behind glass windows in separate metal housings so that a parallel beam of light passed through one half meter of water before striking the photronic cell. This apparatus could be lowered to any desired depth, and the transmission at that depth could be measured with a microammeter. This was converted to percentage transmission through one meter by comparison with a similar reading taken with the apparatus in air. After the formation of the thermocline in Lake West Okoboji the transmission per meter \Vas about 30 per cent for the upper 10 meters, rose sharply between 12 and 13 meters to 46 per cent, remained about constant to 17 meters, rose sharply to 74 per cent at 18 meters, then gradually to 81 per cent between 22 and 28 meters. Below 28 meters the transmission dropped to about 70 per cent. These data are being studied in relation to the distribution of plankton. The average transmission of Lake East Okoboji was about 0.0002% per meter and varied only slightly with depth.

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Proceedings of the Iowa Academy of Science





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© Copyright 1939 by the Iowa Academy of Science, Inc.



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