LIMNOLOGICAL OBSERVATIONS IN THE UPPER MISSISSIPPI. 
405 
Table 26 . — Plankton of the Mississippi River near New Boston, III., July 13, 1921. 
[•, very abundant; Q, abundant; ©, frequent; ©, scarce; O, very scarce; absent.] 
Sturgeon 
Bay. 
Main 
channel. 
Sturgeon 
Bay. 
Main 
channel. 
Volume, cubic centimeters per cubic me- 
ter of water 
5.0 
6.75 
Species— Continued. 
Triarthra longiseta E 
D 
Species: 
Anabsena spiroides K1 
o 
Brachionus backeri v. cluniorbicu- 
Iaris S 
0) 
Melosira crenulata K 
8 
8 
6 
pala v. amphiceros E 
<J 
O 
Cyclotella menenghiniana B 
Pleurosigma spenceri W. S 
Stephanodiscus niagarae E 
Scenedesmus quadricauda Breb 
Pediastrum duplex M 
Eudorina elegans E 
Platydorina caudata K 
Trachelmonas schauinslandii L 
pala v. dorcas f. spinosa W 
angularis caudatus B and D 
Notops clavulatus E 
8 
8 
l 20 
6 
Q A 
H 'g • | 
Asplanehna amphora H 
Sida crystallina O. F.M 
6 
s 
, n .o. l( . 
Cyclops sp 
Detritus 
8 
8 
8 
3 
o 
Sand , 
Euglena spirogyra E 
acus E 
1 Individuals per cubic meter of water. 
The composition and the amount of plankton in the river near Bur ling ton at 
the head of Lake Keokuk are the same as in the main channel at New Boston. 
Rock Island Rapids divide the river into two sections, different as regards their 
plankton contents. Below the rapids the Mississippi carries a little plankton; 
above the rapids the production of plankton in the river is about three times greater. 
This can easily be seen from an examination of Table 27, in which are presented 
the results of the observations made on August 11 and 12 at stations 50 and 51, 
the first of which is located 12 miles below the head of the rapids and the latter 27 
miles above the head of the rapids. 
Table 27. — The composition of the plankton of the Mississippi River at stations 50 and 51, August 11 and 12. 
[#, very abundant; 3, abundant; ©, frequent; 0, scarce; O, very scarce; absent.] 
Rock 
Island 
Rapids, 
station 50. 
Six miles 
above 
Clinton, 
station 51. 
Rapids, 
station 50. 
Six mile 
above 
Clinton, 
station 51. 
Volume of plankton, cubic centimeters 
per cubic meter of water 
Species: 
Clathrocystis aeruginosa H 
Anabsena flos-aquse Breb 
planktonica Brdb 
Melosira crenulata K 
Fragilaria crotonensis K 
Stephanodiscus niagarae E 
Actinastrum hantzc’nii Lag 
Scenedesmus quadricauda Brdb 
Pediastrum duplex M 
Staurastrum sp 
5.0 
15.7 
Species— C ontinued . 
Difflugia pyriformis P 
Arcella sp 
Brachionus angularis G 
Anursea cocblearis G 
cocblearis tecta G 
Daphnia longispina O. F. M 
Bosmina longirostris O. F. M. 
Dia] ’ 
Copej 
Nauplii. 
Detritus 
1 Individuals per cubic meter of water. 
Although the composition of the plankton taken at the two stations was 
essentially the same, there was considerable difference in the quantity of organisms, 
especially of the diatoms and copepods, which were abundant in the river above the 
rapids and scarce below the rapids. The composition of the plankton in the upper 
part of the river was almost the same as at station 51. The amount of plankton, 
however, increased progressively up the river and near Prairie du Chien, Wis., 182 
miles above, was about twice as great as at Clinton (station 51), reaching 32 cm. 3 per 
