PROGRESS IN BIOLOGICAL INQUIRIES, 1931 471 



upon the problem of photosynthesis in these strata as well as in the deeper 

 water. In Crystal Lake, for example, abundant growths of the moss Drepano- 

 cladus aduncus var. (tquaticus are found on the bottom at depths of 18 to 21 

 meters, and similar growths of this plant are found in Weber Lake at depths 

 of 11 to 13.5 meters. Such growths of plant material at these depths raised 

 the question of the amount of solar energy present there for the process of 

 photosynthesis. A number of observations taken in different years and at dif- 

 ferent times during the summer show that from 1 to almost 4 per cent of the 

 solar energy that is delivered to tlie surface of the lake penetrates to a depth 

 of 20 meters in Crystal Lake, while nearly 2 per cent reaches a depth of 13 

 meters in Weber Lake. These amounts of energy seem to be suificient to enable 

 this moss to carry on photosynthesis and grow profusely at these depths in 

 spite of the fact that the summer temperature of the water varies from 7° to 

 12° C. at IS to 20 meters in Crystal Lake, and from a little less than 9° to 

 15° at 13 meters in Weber Lake in the different years. 



A stratum of water possessing an excess of dissolved oxygen was found in 

 Silver Lake on August 28, 1931, and this excess represented oxygen that had 

 been liberated in this region through the photosynthetic activities of the phyto- 

 plankton. The quantity of dissolved oxygen at 9 meters on this date was 

 13.2 milligrams per liter, which was equivalent to 127 per cent of saturation, 

 and there was also a slight excess at 10 meters. Solar-energy readings taken 

 during the summer showed that about 1^^ per cent of the amount of energy 

 delivered to the surface of the lake penetrated to a depth of 9 meters and 

 somewhat less than 1 per cent reached 10 meters. These results seem to indi- 

 cate that the phytoplanktou as well as the moss Drepanocladus are able to 

 carry on the process of photosynthesis in the lower strata of a lake when the 

 solar energy is reduced to about 1 per cent of the amount delivered to the 

 surface. 



Regular observations were made on the temperature and dissolved gases of 

 the six lakes selected for the fish studies. Dissolved oxygen determinations 

 were made for the purpose of obtaining some idea of the most suitable strata 

 for fishing operations in the various lakes ; this was true especially in Muskel- 

 lunge, Nebish, and Silver Lakes, where there is a paucity of oxygen in more 

 or less of the hypolimnion during the summer period of stratification. The 

 general results of such analyses have been incorporated in previous reports, 

 so they may be omitted here. 



Some chemical determinations were made on the waters from about a hun- 

 dred wells and springs situated in the vicinity of the various lakes. These 

 analyses were made for the purpose of obtaining a comparison between the 

 quantity and quality of the substances held in solution by the ground waters 

 and those found in the neighboring lake waters. The general results of these 

 analyses show that the ground water is " softer " than that of the neighboring 

 lake in some instances, in other cases the two are about the same, while in 

 still others the ground water is " harder " than the lake water. Further work 

 on this problem will be necessary before any definite conclusions regarding the 

 relationship between ground and lake waters in this district can be reached. 

 Residues from about a hundred wells and springs were secured during the 

 summer, and further analyses of them will be made at the first opportunity 

 for such work. 



The biological work consisted of (a) a quantitative study of the plankton 

 of the six selected lakes, (ft) a quantitative study of the bottom fauna of these 

 lakes, (c) a qualitative and quantitative study of the food eaten by the fish, 

 and (d) a study of the internal parasites of the fish. Material was also col- 

 lected for an in^'estigation of the rate of growth of the different species of fish 

 that are found in the various lakes. 



Muskellunge Lake yielded the largest average standing crop of plankton 

 organic matter and Clear Lake the smallest, 1.15 grams per cubic meter and 

 0.58 gram, respectively. The volume of Silver and Weber Lakes has been 

 determined, so that the average standing crop of the entire lake may be com- 

 puted for them. For Silver Lake the average amount of dry organic matter in 

 the standing crop of plankton was a little over 10,000 kilograms, which was 

 equivalent to somewhat more than 100,000 kilograms of living material ; the 

 dry weight represented 115 kilograms per hectare of surface, or 102 pounds 

 per acre, while the living weight was approximately ten times as large. 



128210—32 3 



