It is evident from these results that chemical conditions under 

 the ice as late as the first week in February were far from any point 

 which could be regarded as unfavorable to life in the water. The winter 

 of 19?9-1930 was somewhat abnormal in that the months of November and 

 December, 1929, and January, 1930, were slightly colder than normal, 

 while February, 1930, was decidedly warmer than normal. As a result the 

 ice formed a few days earlier, and disappeared many days earlier 

 than usual. Judging by the rather incomplete information given in the 

 Snow and Ice Bulletins of the United States Weather Bureau, ice formed 

 on the lake about December iS and disappeared about February 2k, so that 

 the samples were taken when the closed period was three fourths com- 

 pleted. It seems improbable that the chemical conditions changed 

 radically in the few days remaining before disappearance of the ice. 



The chemical data obtained under the ice in February, 1930 

 leave a number of questions regarding pollution unanswered. During the 

 sunmer of the same year, it was found that marked oxygen withdrawals 

 were liiTiLted to relatively small areas near the mouths of Maumee and 

 Raisin Rivers, With reduced opportunity for recovery by aeration and 

 photo-synthesis under the ice, a general outward extension of these 

 areas would be expected. However, the results at Station B, one mile from 

 the mouth bf River Raisin, indicate^ that the extension of this 

 region was not great, and probably the same was true for Maumee Bay, 

 although Station D is too far from the river to be of value as an index, 

 As far as the data go, they indicate that chemical conditions under the 

 ice were little, if any, less favorable than those prevailing during the 

 open period. Normally, navigation is closed in this general region for 

 a period of 90 days, or almost three weeks longer than in the winter of 

 1929-30. Whether a closed period of that length or longer would be 

 accompanied by a large reduction in oxygen at the stations sampled re- 

 mains open to some question. It seems unlikely that the actual amount 

 of oxygen would be reduced below the amount present during the summer, 

 although the per cent of saturation might be reduced considerably. On 

 the whole the data do not indicate the need for revision of the con- 

 clusions regarding pollution based on the samples taken in the surrmer. 



Evidence of poisons in the water 



Industrial centers, such as Detroit and Toledo, are sources of 

 large amounts of trade wastes which enter the tributary streams and 

 finally reach Lake Erie, In this investigation, no attempt was made to 

 analyse the water for any of the large number of substances of poisonous 

 nature which might be present. Obviously the magnitude of such a task 

 precluded the possibility of doing it justice in a general survey of this 

 kind. It may be assumed that poisonous substances are present in the 

 water; the question to be decided is whether they are present in suffi- 

 cient concentration to injure or kill the plants and animals in the lake. 

 The answer to this question must be given largel^'^ on the basis of in- 

 direct evidence, 



137 



