BIOLOGICAL SURVEY OF THE UPPER MISSISSIPPI RIVER 



147 



Table 6. — -Relative amounts of residue in bottom samples, expressed in cubic centimeters and per cent, 

 the nature of the residue, and the character of the predominating animals of the bottom fauna 



[S=shore; C=channcl] 



Station 



Sample, 

 cubic 

 centi- 

 meters, 

 before 

 straining 



Sample, 

 cubic 

 centi- 

 meters, 



after 

 straining 



Per 

 cent 



Nature of residue after the animals were re- 

 moved 



Predominating animals in bottom 

 samples 



1 









Clean, coarse sand 



Clean-water forms. 



Tubificidse and Campeloma rufum. 



Tubificidse. 



Tubificidse and bivalves. 

 Tubificidse. 

 Do. 



Clean-water forms. 

 Leeches. 



Leeches, Hyalella, and Tubificidse. 

 Hyalella. 



Aquatic insects (clean-water forms). 



2.. 



450 

 400 



290 

 300 



64 

 75 



Garbage _ _ - 



3 



Cinders; coarse garbage; chips of wood 



5 



Coarse organic debris; sand 



6 



310 

 200 

 250 

 400 

 200 



120 

 150 

 50 

 350 

 175 



38 

 75 

 20 

 87 



87 



Little organic debris; pieces of fat and gray sand_ 

 Organic dSbris 



7-C 



8 .... 



Aquatic plants; cinders; but mostly sand _ 



9 



Shells of bivalves 



9-S. _ 



Aquatic plants; broken-up leaves 



11-S 



Sand and aquatic plants 



14-S 



300 



230 



77 



Mostly coarse gravel; little organic debris... ... 







The sample taken near the right bank of the river, at station No. 1, showed 

 that each square yard of the bottom contained 252 Tubificidse, 36 midge larvae 

 (Chironomus — not the red midge), 36 dragon fly nymphs, 36 specimens of Hyalella 

 Tcnickerbockeri, and 108 individuals of Sphserium sp. ? (a small bivalve). The second 

 sample was taken in the channel near the left bank of the river. Here the substratum 

 consists of pure sand with a few scattered plants. In the channel the Tubificidae 

 are absent entirely. Midge larvae are more numerous (108 specimens per square 

 yard) here than near shore. A number (72 per square yard) of beetle larvae 

 (Elateridae) occur in the channel, but these are not aquatic. Associated with the 

 above forms were four species of animals known to prefer clean, running water. 

 These are Planaria, caddis fly larvae, larvae and pupae of the sand fly (Simulium sp. ?), 

 and May fly nymphs. The residue of the strained sample, after the removal of the 

 animals, consisted of pure sand. 



At station No. 2 the first mud sample was taken in the left branch of the channel 

 at the same place where the seine hauls for fish were made. The bottom here is fairly 

 clean and solid. The only animal taken in this sample was a midge larvae. The 

 second sample was taken some 50 yards below a sewer outlet in the right branch of 

 the river. The difference in these two samples demonstrates the effect of sewage 

 on bottom fauna quite clearly. In the first sample there were only 36 midge larvae 

 per square yard, but in the second there were 15,120 Tubificidae, 1,600 snails 

 {Campeloma rufum), and 54 bivalves (Sphserium notatum) per square yard. The 

 residue of the second sample, after straining and the removal of the organisms, con- 

 sisted of garbage. The results from this second sample are not representative of a 

 cross-section of the river at this place. In the channel of the right branch and along 

 the left branch of the river the bottom is fairly clean. However, as mentioned 

 before, it demonstrates the effect of sewage. 



No reference has been found in the literature to the tolerance of Campeloma 

 rufum in polluted waters, but the above data indicate that very likely it is one of 

 the more tolerant forms. Campeloma subsolidum is classed by Richardson (1925) 

 as one of the less tolerant snails. 



