LIMNOLOGICAL STUDIES OF KARLUK LAKE 
423 
others. In the hard-water lakes of southeastern Wisconsin, the percentage of cal- 
cium shows a maximum of a little more than 17 per cent, while a bottom sample from 
one of the lakes at Lunz, Austria, yielded a little more than 38 per cent of calcium 
and one from Lake Balaton, Hungary, a little more than 37 per cent. 
The percentage of organic carbon is distinctly smaller in the bottom samples from 
the Alaskan lakes than in those obtained from the lakes of northeastern Wisconsin; 
in the latter samples the percentage of organic carbon varied from somewhat more 
than 10 to almost 39 per cent of the dry weight of the deposits. 
Table 11. — Chemical analyses of bottom deposits of Alaskan lakes 
[The samples were taken in 1927 with a small Ekman dredge, so that they represent only the upper 15 cm. of the deposits. The 
results of the analyses are given in percentages of the dry weight of the samples. Upon drying the various samples lost from 
1.43 to 5.19 per cent of moisture] 
Lake 
Date 
Depth 
SiOj 
FejOs 
AljOs 
Ca 
Mg 
PjOj 
so 4 
COi 
Org.C 
Karluk, station 1 
Aug. 13 . 
Aug. 8... 
Meters 
125 
60. 50 
4.93 
6.88 
1.62 
0.44 
1.06 
0. 69 
4. 58 
Karluk, The Thumb 
17 
73. 07 
3.36 
5. 65 
1.86 
.54 
L 37 
. 1.85 
. 70 
5. 34 
Do 
38 
63. 91 
5.45 
11.76 
2.60 
1. 50 
.65 
.44 
.52 
1.95 
Do 
-_.do.-_ . 
40 
66. 10 
7.00 
12.22 
2.05 
1.30 
.82 
.51 
.20 
4. 22 
Karluk, station 3 
July 19.. 
July 21.. 
50 
69.81 
6.05 
5.42 
2.96 
.90 
.92 
1.37 
.67 
5. 05 
Thumb Lake.. 
10 
60.00 
6. 42 
9. 65 
1.89 
1.07 
1.02 
1.78 
.20 
6. 56 
O’Malley Lake 
July 23.. 
12 
71.76 
4.32 
3. 75 
2.71 
.93 
1.35 
1.12 
.80 
8. 50 
PLANKTON DATA 
NET PLANKTON 
Catches of net plankton were obtained from Karluk, Thumb, and O’Malley 
Lakes at the same time that samples were taken for the chemical analyses, and at 
other times also. This plankton material was secured by means of the regular type 
of closing net that has been used in making catches on the Finger Lakes of New 
York, on a number of lakes in northwestern United States, and on various lakes in 
Wisconsin. This type of closing net has been fully described by Juday (1916) so 
that no further description is necessary at this time. The net has a relatively large 
straining surface of bolting cloth in proportion to its opening and numerous tests 
have shown that its coefficient lies between 1.8 and 2; that is, it strains approxi- 
mately half of the water in the column through which it is hauled. 
The plankton material obtained in these catches was enumerated by the usual 
method and the numbers found in each catch were multiplied by 2 in order to 
indicate the total number of organisms in the column through which the net passed. 
The results of these quantitative studies are given in Table 12 in which the average 
numbers of organisms per liter of water are indicated for the different series. No 
attempt was made to count the different species separately; the different forms were 
enumerated by genera, and the various genera were then combined into groups as 
shown in the table. 
The great variety of organisms found in the catches is shown by the following 
list of genera which are represented in the material. 
Cladocera: 
Alona. 
Bosmina. 
Chydorus. 
Daphnia. 
Holopedium. 
Copepoda: 
Cyclops. 
Diaptomus. 
Epischura. 
Rotifera: 
Anuraea. 
Rotifera — Continued. 
Asplanchna. 
Asplanchnopus. 
Brachionus. 
Conochilus. 
Conochiloides. 
Rotifera — Continued . 
Diplois. 
Diurella. 
Floscularia. 
Gastropus. 
Monostyla, 
