their most probable positions. No data are available for the area near 

 the mouth of Ottawa River. The areas included in the zones of pollution 

 as shown in Figure 23 are as follows: heavy pollution, 2h.9 square kilo- 

 meters (9.6 square miles); moderate pollution, 12.9 square kilometers 

 (5.C square miles); light pollution, 39.1 square kilometers (l5.1 square 

 miles). The total area of polluted bottom in the Maumee Bay Section 

 was therefore 76.9 square kilometers (29.7 square miles). In view of 

 the fact that the shoreward extensions of the zone-limits are not based 

 on data, no importance should be attached to the decimals in the figures 

 given above. 



River Raisin Section 



Station 117 



The only regular station established in this section was 

 Station 117, located 2 miles ESE l/8 E of Monroe Light. The bottom at 

 this point is composed of sand, with a small amount of gravel and 

 organic debris. The results obtained in 1929 and 1930 are shown in Table 91. 

 It may be seen that no organism or group of organisms was particularly 

 abundant in either year. In 1929 the average count of Tubificidae was 

 21 per square meter, while in 1930 the average count was lOU per square 

 meter. The mayfly larvae were rare in both years, but especially so in 

 1930, Their rarity is readily explained by the type of bottom; hence it 

 cannot be taken as an index of the presence of pollution. Using the 

 tubificid worms as the only index organisms, and applying the criteria 

 of pollution as set forth in the introduction to this chapter, it is 

 evident that this station should be assigned to the zone of clean bottom 

 for 1929 and to the zone of light pollution for 1930, 



In seeking an explanation for a similar difference in the data 

 of the two years at Station 25U, it was noted that the organisms were not 

 uniformly distributed. However, at Station 117 there is no channel to 

 confine organic debris derived from the river and give rise to unusually 

 large differences in distribution of the organisms. The difference in 

 the data of the two years probably resulted from actual shifting of the 

 organic debris. The bottom is composed of sand and there is little 

 opportunity for intimate mixing of the organic matter with the bottom 

 deposits as in the case of mud bottom. Thus the accumulations of debris 

 lying on the sand would be cJisturbed and moved about by currents and 

 large waves. If it is true that there is a more or less constant 

 shifting of the bottom materials, it is obvious that a few samples taken 

 at one station would give a very incomplete picture of the situation with 

 regard to pollution in this general area. For that reason, a considerable 



282 



