432 BULLETIN OF THE BUREAU OF FISHERIES 
Table 14. — Number of phytoplankton organisms per liter of water at various depths in hand centrifuge 
catches taken in Karluk Lake, station 2, and in Thumb Lake in 1927 
Organisms 
Karluk Lake, Aug. 8 
Thumb Lake 
Aug. 3 
Aug. 12 
0 
5 
10 
15 
25 
40 
0 
10 
0 
5 
10 
Green algse: 
Ankistrodesmus 
Meters 
Meters 
Meters 
Meters 
Meters 
Meters 
Meters 
Meters 
Meters 
Meters 
70, 560 
105, 843 
Meters 
Chlamydomonas 
70, 560 
211, 685 
17, 640 
23, 520 
70, 560 
70, 560 
70, 560 
211, 685 
70, 560 
Staurastrum..- 
Scenedesmus 
105, 825 
23, 520 
Diatoms: 
Asterionella 
141, 123 
211, 685 
23, 520 
Amphora _ 
17, 640 
23, 520 
70, 560 
23, 520 
Cyclotella 
70, 560 
70, 560 
Fragilaria__ _ 
141, 123 
776, 178 
141, 123 
35^ 280 
423, 370 
Melosira. 
70,560 
23, 520 
35, 280 
917, 300 
917, 300 
70, 560 
Navicula 
Synedra 1 
35, 280 
17, 640 
70, 560 
35, 280 
94, 082 
70, 560 
35, 280 
Stephanodiscus 
70, 560 
Tabellaria 
70, 560 
The net catches taken in Thumb Lake on August 3, 1927, contained no green 
algae, but the diatoms numbered 985,000 per liter of water. The surface and bot- 
tom centrifuge catches taken on this date gave an average of 70,500 green algae and 
1,377,000 diatoms per liter; the diatoms, therefore, were less than twice as numerous 
in the centrifuge catches as in the net material. In the net and centrifuge catches 
taken in Thumb Lake on August 12, 1927, the average number of diatoms in the 
former was 889,000 per liter and in the latter 788,000 per liter; in this case the net 
catches yielded a larger number of diatoms than the centrifuge samples. 
Net and centrifuge samples taken in Lake Mendota at Madison, Wis., over a 
period of two and a half years showed that the latter yielded on the average about 
five times as much dry organic matter as the former; at certain times the organic 
matter in the centrifuge plankton was about the same in quantity as that in the net 
plankton, but at other times it amounted to about twenty-five times as much as 
that in the net plankton. 
SUMMARY 
1. The area, maximum and mean depth, volume, temperature, and heat budget 
of Karluk Lake are given. 
2. The chemical results show that the surface water was alkaline (pH 8.6) and 
that at 125 meters was neutral (pH 7); the water contained an abundance of dis- 
solved oxygen at all depths during the summer, hence it belongs to the oligotrophic 
type of lakes; the water contained only 9 to 10 milligrams of fixed or bound carbon 
dioxide per liter. 
3. The soluble phosphorus in Karluk Lake varied from 0.002 milligram in the 
surface water to 0.018 milligram per liter in the lower water; the organic phosphorus 
ranged from 0.003 to 0.028 milligram per liter in the surface water and from 0.012 
to 0.014 milligram per liter in the lower water. 
4. The titratable silica ranged from 0 to 0.6 milligram per liter. 
5. Very little 'ammonia nitrogen was found in the surface water of Karluk Lake, 
but 0.12 milligram per liter was present in the bottom sample from station 2. Prac- 
tically no nitrite nitrogen was present. The nitrate nitrogen ranged from 0.012 
milligram in the surface water to 0.052 milligram per liter in the bottom water. 
