PROGRESS IN- BIOLOGICAL, INQUIRIES, 19 3 585 



plan to take up more intensive work on a few lakes which represent the various 

 types that have been found in the district. 



In 1930 as in 1929 a large amount of work was done with the pyrlimnom- 

 eter on the relation between solar radiation anil the lakes. A new line of 

 study was entered upon, namely the composition of the energy spectrum as 

 determined l)y the use of light filters. It was found that in this way accurate 

 and detailed knowledge can be secured of the distribution of the radiation at 

 different depths in lakes, to the several regions of the spectrum. Since at 

 depths of 1 meter, and over, practically only visible radiation remains, this 

 study is concerned with the quantitative distribution of light in the lakes. 

 It is possible to ascertain not only the quantity of light present at any depth 

 within the competence of the instrument, but also the percentage of the quan- 

 tity that is present, ^as, say a yellow light, or from the region of the spectrum 

 between 5000-6000 A. It is exi^ected that this study will serve as a basis for 

 the investigation in lakes of the relations between light and the growth of 

 algae — the fundamental food supply of lakes. 



Work was continued on the studies of 1929 relating to the transmission of 

 total radiation also as well as that of the several colors. The season was very 

 favorable for these studies. Fifty-one lakes were visited, many of them sev- 

 eral times, and 74 series of observations were made which included more than 

 9,700 readings of the pyrlimnometer. 



Determinations of hydrogen-ion concentration, carbon dioxide, dissolved 

 oxygen, oxygen consumed, and calcium were made on 239 different lakes during 

 the summer. The dry organic matter in the centrifuge plankton was deter- 

 mined on 252 samples and 139 samples of water were evaporated in order 

 to obtain residues for further chemical analyses. 



A wide variation in organic and mineral content was found in the various 

 lakes ; the dry residues ranged from a minimum of 13 to a maximum of 116 

 milligrams per liter of water. Likewise there was a wide range in the con- 

 ductivity of the water, varying from 8.5 to 115 when expressed in terms of the 

 reciprocal of the megohms resistance. The color of the water in these lakes 

 varied from none to a maximum of 240 based on the U. S. G. S. standards of 

 the platinum-cobalt scale. This wide variation in color causes a correspond- 

 ingly wide variation in the rate of absorption of the sun's energy by the waters 

 of the various lakes. 



The hydrogen-ion concentration ranged from pH 4.8 to 8.6 ; the lowest values 

 were found in the very soft water lakes and the highest ones in the lakes with 

 considerable amounts of fixed carbon dioxide and with abundant growths of 

 phytoplankton. The fixed carbon dioxide ranged from 0.7 to 31 milligrams 

 per liter of water ; the smallest amounts were noted in lakes that have neither 

 an inlet nor an outlet. 



The dissolved oxygen in the surface water varied from 5.8 to 10.6 milligrams 

 per liter ; the smaller quantities of oxygen were found in lakes that possessed 

 boglike conditions while the larger amounts came from lakes supporting an 

 abundant growth of phytoplankton. 



The oxygen consumed, as determined by the permanganate method, ranged 

 from aljout 1 milligram to 26 milligrams per liter of surface water. It was 

 usually somewhat lower in the bottom than in the surface water of the deeper 

 lakes. This determination gives a general idea of the amount of organic matter 

 present in a readily oxidizable condition in the water. There is a certain 

 degree of correlation between the quantity of oxygen consumed and the amount 

 of vegetable coloring matter in the water. 



The quantitative studies of the iron showed that only a small amount is 

 present in the surface water. The quantities ranged from a trace to 0.26 mil- 

 ligram per liter of water in the various lakes. Larger amounts were found 

 in the lower water of the deeper lakes in some cases, especially where the 

 dissolved oxygen all disappeared from the lower stratum in summer. 



The quantity of calcium in the surface water varied from a minimum of 

 a little less than 0.2 milligram per liter to a maximum of 20 milligrams, a 

 hundredfold difference. The lakes that have neither an inlet nor an outlet 

 possess the smallest amounts. The quantity of calcium is approximately 50 

 per cent as much as that of the fixed carbon dioxide, more especially when the 

 fixed carbon dioxide is 5 milligrams per liter or more. 



Several thousand specimens of the aquatic Mollusca have been collected in 

 this lake district during 1929 and 1930. A taxonomic report on the various 

 species and their distribution in that region is almost completed. One of the 



