LIMNOLOGICAL OBSERVATIONS IN THE UPPER MISSISSIPPI, 
395 
Table 21. — Mean amount of plankton and mean number of Copepoda and Cladocera in cross sections of 
Lake Pepin, August to September, 1921 . 
Station number. 
Distance 
from the 
head of 
the lake. 
Copepoda, 
mean num- 
ber per 
cubic 
meter. 
Cladocera, 
mean num- 
ber per 
cubic 
meter. 
Mean vol- 
ume of 
plankton, 
cubic cen- 
timeters 
per cubic 
meter. 
96 to 98 
0 
3, 000 
600 
16.5 
88 to 90 
1.5 
11,200 
600 
9 
84 to 86 
3 
42,000 
4,300 
16 
81 to 83 
4.75 
9,000 
1,500 
16 
78 to 80 
6 
19,000 
500 
15 
71 to 73 
9 
13, 000 
500 
15.1 
74 to 76 
13.5 
34,000 
700 
16.2 
58 to 60 
15 
22,000 
1,000 
22.6 
62 to 64 
18.5 
60,000 
1,100 
23.5 
65 to 67 
20.5 
35,000 
400 
21.3 
68 to 70 
22.25 
30, 000 
120 
22.2 
101 to 103 
24.5 
20,000 
200 
18.5 
Fig. 17— Distribution of Crustacea in Lake Pepin. (The mean content of plankton and the mean numbers of Copepoda and 
Cladocera in cross sections of Lake Pepin, August-September, 1921, from head of lake down to the foot. Stations 96-98 are 
located at the inflow of the Mississippi River; stations 101-103 at the outflow of the lake. Heavy line, — , represents 
the mean volume of plankton per cubic meter of water; plain line, , number of Copepoda per cubic meter of water; 
dotted line, , number of Cladocera per cubic meter of water. The figures on the lines are the averages computed from 
the data of three stations on the given cross section of the lake. The serial numbers of stations are given under the abscissae. 
Scale: One division of the abscissa— 1 mile; one division of the ordinata— 5 cm. 3 of plankton for heavy line, 10,000 individ- 
uals of Copepoda for plain line, and 1,000 individuals of Cladocera for dotted line.) 
