One of the striking features of the lata from stations other than 

 Station 2U9 is the small amount of nitrogen as nitrite and nitrate. At 

 Station 25o, where free and albuminoid ammonia werr many times higher than 

 in the Island Section, nitrite was only slightly higher, and nitrate was 

 lower. This finding is contrary to exr^ectation. In general, surface waters 

 contaminated by sewage have a high concentration of nitrite and nitrate as 

 well as of free and abluminoid ammonia. This general rule does not hold for 

 fresh sewaj^e itself, because time is required for nitrifying bacteria to 

 change the free ammonia to niftrite and nitrate. Mason (1917> page 58) gave 

 some figures on fresh sev/age at Troy, New York. Although free and albuminoid 

 ammonia were high, there was no nitrate and only a trace of nitrite in the 

 sewage. Low nitrite and nitrate at Station 2^0 cannot be explained entirely 

 by lack of time for their formation, because at Station 2l49j in the river, 

 nitrite wa'^ very high, and nitrate was higher than at Station 250. Moreover, 

 the stations farther out from the river showed little nitrite and nitrate in 

 the presence of abundant decomposing organic irntter. A possible explanation 

 for low nitrite and nitrate at Station 250 is that the denitrifying bacteria 

 were unusually active in Maumee Bay, but there is no reason for assuming that 

 they were more active than the nitrifiers. Lack of oxygen for the process o.' 

 nitrification probably was not an important factor, for only at Station 2li9 

 was oxygen consistently low, and nitrite and nitrate were more abundant there 

 than at the stations well supplied with oxygen. 



The most probable explanation is one which involves the abundance of 

 phytoplankton in Maumee Bay. On the dates in 1930 for which data are availablCj 

 phytoplankton was more abundant at Station 2$0 than at Stations 252 and 25U, 

 and the mean abundance at these last two stations was about six times as great 

 as in the Island Section (Table 62). The principal factor involved in the 

 great production of phytoolankton at Station 250 is believed to be the high con- 

 centration of nutritive materials in the .water of the river, ijhen the water 

 of Maumee River enters Maumee B^y it contains an abundance of nitrogen avail- 

 able to plants. Free a-imonia is particularly abundant because it is a natural 

 constituent of sewage, while nitrite and nitrate must be forined from it by 

 the action of nitrifying bacteria. However, it is safe to assume that nitrite 

 and nitrate are formed in large quantities. Presumably the algae sieze upon 

 the abundant nutritive materials and increase to such great numbers that they 

 are able to remove almost all of the nitrite and nitrate as soon as these 

 compounds are formed. Free ammonia remains relatively high, possibly because 

 it i 3 formed more rapidly than nitrite and nitrate, or possibly because it is 

 less readily utilized by the algae. In either case, it seems probable that 

 utilization of the great excess of ammonia permits the maintenance of algae 

 in sufficiently large numbers to keep nitrite and nitrate at low concentra- 

 tion, in spite of the fact that these compounds are formed in large amounts. 

 Accoriling to this view, if it were not for the extra stimulation to growth 

 afforded by the free ammonia, nitrite and nitrate would be much more concen- 

 trated at Station '25c than in the Island Section. 



The results at Stations 252 and 2514, are in accord, on the i>/hole, with 

 the explanation presented , above. Table 33 and Figure 18 shows that at Sta- 

 tion 252 there was much less free and albuminoid ammonia than at Station 250, 

 and hence less nutritive material, both ore-formed and potential, for the 



109 



