BIOLOGICAL SURVEY OF THE UPPER MISSISSIPPI RIVER 



149 



odor of the sample was distinctly foul and oily. The sample yielded 10,800 Tubificidse 

 and 85 specimens of Musculium near transversum and near truncatum per square yard. 



The sample from the Minnesota River (station No. 4) yielded 108 Tubificidse 

 per square yard. Besides the organisms, a few grains of coarse sand were left in the 

 strainer after the sample had been washed with tap water. 



The last of the extra samples (see p. 148) was taken just above the Jackson Street 

 Bridge, about one-half mile above station No. 5. A sample taken here on September 

 27 yielded 2,880 Tubificidse, 144 Chironomus larvse, and 36 leeches per square yard. 

 This sample was taken partly along shore and partly in the channel. 



At station No. 5 no bottom samples were obtained in the channel. The current 

 was rather swift in the channel, and with the prevailing high waters its bottom was 

 kept fairly clean from deposits. 



The first sample taken along shore at station No. 5 consisted (besides the animals 

 it contained) of coarse sand and a considerable amount of organic debris. The 

 sample yielded 144 midge larvse, 11,970 Tubificidse, and 1,620 bivalves per square 

 yard. The bivalves were made up of Musculium near transversum, M. near trun- 

 catum, and a few specimens of Pisidium. This is the first instance where these 

 bivalves occur in such large numbers. Both the worms and the bivalves are an 

 indication of pollution. 



The second sample at No. 5 was taken in a slough permanently connected with 

 the river. The reason for taking the sample in the slough was the fact that what 

 was shore when the first sample was taken (August 17) was now (September 15) 

 channel, and the bottom deposits had been carried away. This slough now formed 

 a part of the shore. One dredge haul here yielded a sample of 700 cubic centimeters, 

 200 cubic centimeters of which were strained. In addition to the fauna, the residue 

 of 50 cubic centimeters consisted of sand and Elodea. Each square yard of the 

 bottom here contained 3,240 midge larvse, 5,832 Tubificidse, and 1,157 leeches. 



The first bottom sample at station No. 6 was taken near shore in shallow, swiftly 

 flowing water. The sample showed that each square yard of the bottom contained 

 2,520 Tubificidse. The residue left after the sample had been washed consisted of 

 coarse sand. In September, two bottom samples were taken a little farther down- 

 stream, where the strength of the current was reduced greatly by wing dams. One 

 sample was taken near the left bank of the river and the other near the right bank. 

 The former yielded 75,400 Tubificidse per square yard and the latter 10,260. The 

 sample from the right bank contained several pieces of fat, a little organic debris, 

 and gray sand. 



The condition of the bottom at station No. 7 is the worst that was met below 

 Minneapolis. When the first visit to this station was made (August 18), gas bubbles 

 (nature of gas not known) were rising continually, not only along the shore but also 

 in the channel. From time to time large pieces of solid material came to the surface. 

 As mentioned above (p. 141), the current here is rather slack, and this facilitates the 

 settling out of the solid materials. The organic materials presumably ferment at 

 the bottom, partly, perhaps, under anserobic conditions. The gases resulting from 

 these fermentations undoubtedly are responsible for raising large masses of solids to 

 the surface. The bottom samples taken on August 18 consisted (besides the animals 

 they contained) entirely of organic debris. The sample had an extremely foul odor. 



