54 THE LIFE OF DEVILS LAKE 



analysis of the water and the determination of its inhabitants. A 

 few records of temperature and dissolved gases for 1918, indicate 

 very similar conditions to those of Main Lake (figs. 13-15). 



The deepest part of the lake (7.6 m. in 1918) is near the 

 southeastern end of the main body. Thence the lake gradually 

 shallows in both directions, while the western arm in 1918 did not 

 exceed a depth of 3 m. at any point. The bottom is covered with 

 an ooze, similar to that on the floor of Devils Lake. 



The chemical anah^sis and osmotic pressures are shown in table 

 3. There is a much greater amount of dissolved substances due to 

 the higher chlorine and sulphate content, with a correspondingly 

 greater osmotic pressure. A considerable part of the chlorine is 

 present as NaCl, as evidenced by the distinctly salty taste of the 

 water, which is lacking in Main Lake, or concealed by other in- 

 gredients. 



The same life zones occur as in Main Lake, and the constituent 

 organisms are similar. No extensive plancton studies have been 

 made and there are no coincident records from Main Lake for com- 

 parison. The few collections made in 1918 indicate, however, a 

 comparative scarcity of rotifers, a fairly average number of crust- 

 aceans and a considerable abundance of Nodularia and Chaetoceros. 

 The distribution of the latter is evidently local however, as it ap- 

 peared in large numbers (1000-1500 cells per cc.) at the eastern 

 end of the lake on July 10, 1918, while only from 20 to 40 cells 

 per cc. were present at the southwest end, about eight miles distant 

 the following day. 



The considerable abundance of Nodularia is of interest, as 

 this alga appears to increase with increasing salt content, at least 

 up to a certain limit. In East Lake also there was an enormous 

 amount of Nodularia present in 1913-14, correlated possibly with 

 the greater concentration of its water. But, on the other hand, no 

 increase of this alga has been detected in Main Lake since 1911, 

 while the concentration of its water has materially increased since 

 that time,* so that the reason for its abundance in East and Stump 

 Lakes is uncertain. 



LAKE A (pl. 9). 

 This small lake was cut off from the main body about 1885. 

 It is approximately 1.3 sq. km. in extent, with a maximum depth of 

 about 2.5 m. While there has been a marked drop in the level of 

 the lake since its isolation, it is, at present, fairly constant in level, 

 due undoubtedly to a small supply from springs. At one point a 

 very slight stream trickles into the lake, and there is probably some 

 underground seepage. Kun-off and rainfall can hardly be ade- 



*Cp. the charts of distribution of Nodularia in Main and East Lakes (pl. 15 and 

 fig. 20) with the chemical anals'ses (table 3.) 



