(11.7 square miles). The total area of polluted bottom in this section 

 in 1930 was therefore 32.8 square kilometers (12.6 square miles). 



Detroit River Section 



Regular Stations 



Only two regular stations were established in what has been 

 designated as the Detroit River Section. One of these is Station 126, 

 located very close to the outer end of the west or down-bound channel 

 as the latter was situated in the summer of 1929. Before sampling 

 was begun in 1930, dredging operations had extended the channel south- 

 ward about 6000 feet, but apparently had not disturbed the bottom at 

 Station 126, The bottom material at this station was composed principally 

 of mud, with an admixture of sand and organic deoris. Judging by 

 odor, and general appearance of the residue following washing, the 

 amount of decajang organic matter was much less here than at the mouths 

 of Maumee and Raisin Rivers. 



The results obtained from I6 Samples taken in 1929 and 

 5 samples taken in 1930 are shown in Table 96. It is obvious from 

 the number of Tubificidae and the absence of Hexagenia that this 

 station was lightly polluted in both years. In view of the fact that 

 in 1930 Station 25U (Toledo Harbor Light) had quite a number of 

 Kexagenia along with 5olj tubificids per square meter, it appears 

 probable that the absence of Hexagenia at Station 126 was due to the 

 presence of considerable sand rather than to the degree of pollution. 

 Comparing counts for the two years at Station 126, it will be noted 

 that the total number of individuals was greater in 1929 than in 1930, 

 This difference resulted from an apparent small increase in three of 

 the groups and a rather large increase in five of the groups represented. 

 In 1928, 8 samples were taken on two dates. The means for the two 

 dates were l50 Tubificidae and 182 Chironomidae per square meter. Only 

 a few other forms were taken. 



The second regular station is Station 13li, located 6 l/U miles 

 due west of Middle Sister Island, which places it 8 miles S. by E. from 

 Station 126. Here the bottom material was mud of the same appearance 

 and consistency as that found at the regular stations in the Island 

 Section. The results obtained from 12 samples in 1929 and 8 samples in 

 1930 are shovm in Table 96. There was no evidence of pollution at this 

 stationj the tubificid count was well below the number considered in- 

 dicative of pollution, and the mayfly count was high, especially in 

 1930, The general make-up of the bottom fauna was much like that of 



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