which in turn determines 'Hght penetration. The amount of carbon 

 dioxide ( not indicated as such on the chart ) is regulated by a num- 

 ber of factors shown in this chart. Carbon dioxide plays an important 

 role, of course, because of its relationship to photosynthesis and 

 hence to the amount of plant life. 



As has been pointed out by Chandler ( 1944 ) all these factors fall 

 into three groups or classes : edaphic, morphometric, and climatic. In 

 this paper he relates seasonal pulses and annual variations in the 

 quantity and quality of the phytoplankton to some of these factors. 

 He found the most important to be turbidity, solar radiation, and 

 temperature. 



CHLOROPHYLL AS AN INDEX OF 

 PRODUCTION 



It is sufficient to say that chlorophyll in water plants, as in land 

 plants, is the all-important agent and initiator in a series of physical- 

 chemical changes which culminate in and are responsible for the 

 fauna. In this connection, mention should be made here of the pos- 

 sible use of chlorophyll measurements as indirect, if not direct, in- 

 dices of potential productivity. 



An approach to such an evaluation of production has been de- 

 scribed by Kozminski (1938). He secured acetone extractions of 

 chlorophyll from the phytoplankton at different lake levels and then 

 made quantitative readings by measuring the absorption of light 

 waves 6200-6800 A in length. By this photometric method he was 

 able to secure an index of phytoplankton production in terms of the 

 amount of chlorophyll at different lake levels. By plotting the chlor- 

 ophyll (expressed in Mg./M^) against depth in meters a useful in- 

 dex of the amount of phytoplankton at different levels is obtained. 

 Then when the curves from various lakes are compared an evalua- 

 tion of respective productivity potentials is established on the basis 

 of the available chlorophyll. ( See Fig. 8. ) 



It is interesting to correlate these readings (Fig. 8) with the qual- 

 ity of the phytoplankton and limnological characteristics. In Scaf- 

 fold Lake, Wisconsin, for example, there is shown to be very great 

 absorption of light in photometric tests, especially between 2 and 8 

 meters, and we find a very dense flora of nannoplankters. At the time 

 observations were made, the lake had a peculiar bluish-tan color from 

 a tremendous population of the chlorobacteriacean Pelogloea bacil- 

 lifera. This is a colonial organism with minute cells rather loosely 

 held in soft mucilage. In a plankton net, the aggregates usually 

 break up and only individual cells or small clumps appear when the 



[36] 



