LIMNOLOGICAL STUDIES OF KARLUK LAKE 
415 
Table 7 shows the results of the temperature readings on Thumb and O’Malley 
Lakes. The surface temperatures of these two lakes did not differ greatly from those 
of Karluk Lake on corresponding dates; the maximum difference was noted in 1929 
when the surface water of O’Malley Lake had a temperature of 16° C. (60.8° F.) 
on July 10 and that of Karluk Lake was 13.2° C. (55.8° F.) on July 9. The maxi- 
mum difference between surface and bottom temperatures in Thumb Lake was 
4.2° C. on July 11, 1929, and a difference of 4° C. was noted in O’Malley Lake on 
July 10, 1929. 
Table 7. — Summer temperatures of Thumb and O’Malley Lakes 
[The readings are indicated in degrees centigrade] 
CHEMISTRY OF LAKES 
Table 8 shows the results of the chemical analyses that were made on the waters 
of Karluk, Thumb, and O’Malley Lakes during July and August, 1927. In Karluk 
Lake the hydrogen-ion concentration ranged from pH 8.6 at the surface to pH 7.0 
at a depth of 120 meters. In Thumb Lake the hydrogen-ion readings were some- 
what lower, ranging from pH 8.2 at the surface to pH 6.8 at the bottom, while in 
O’Malley Lake the readings were still lower, being pH 8.0 at the surface and pH 6.6 
at the bottom. 
In Karluk Lake the free carbon dioxide amounted to 1 milligram per liter of water 
at the surface and to 3.5 to 4 milligrams at the bottom. In both Thumb and O’Malley 
Lakes the free carbon-dioxide content was somewhat larger in the bottom water than 
in the main basin of Karluk Lake, but the quantity found in the lower water of the 
Thumb Basin of Karluk Lake on August 2, 1927, was a little greater than that in the 
lower water of Thumb Lake. The fixed or bound carbon dioxide in Karluk Lake 
varied between 9 and 10 milligrams per liter of water and O’Malley Lake had the 
same amount; the quantity was a little larger in Thumb Lake, namely 11 to 12 
milligrams per liter. This relatively small quantity of fixed carbon dioxide indicates 
that these waters contain correspondingly small amounts of carbonates in solution, 
and this comparatively small carbonate content is due to the fact that the country 
rock of this drainage basin consists chiefly of slate. 
