in numbers at Station 2^2 was due largely to the greens and blue- 

 greens, for in many cases, particularly in 1930, diatoms were more 

 numerous at Station 2514. Except for two dates in 1929, the plankton 

 was more abundant at Station 250 than at Station 25U. The total 

 counts at Station 25U were consistently higher than the averages for 

 the Island Section on comparable dates (Tables $1 and S3) » 



General Stateinent . The most outstanding feature of the 

 phytoplankton of the Maumee Bay Section is the great abundance as 

 compared with the Island Section. A second notable featui-e is the 

 decline in" abundance with increased distance from Maumee River, 

 A third is the dominance of blue-green algae over greens, and of 

 greens over diatoms, in 1930, when the most adequate data were ob- 

 tained. Exceptions to all of these statements may be found in 

 individual samples, but they appear to be true in general. 



It seems probable to the writers that two factors are of 

 especial importance in causing the great abundance of phytoplankton 

 in this region, namely, depth of water, and abundance of nutritive 

 materials in the water. It is well known that shallow bodies of 

 water, in general, produce rfcre plankton per unit volume of water 

 than deep bodies of water of the same region. It is likely, then, 

 that Maumee Bay was more densely populated with plankton than the 

 Island Section even before man influenced the character of the water. 

 It has been shown in the chapter on chemistry (p. lOU) that the 

 water of Maumee Bay contains much more nitrogen than the water of 

 the open lake. Likewise it contains more free carbon dioxide and 

 calcium bicarbonate. Without doubt the algae have increased greatly 

 as a result of this added supply of raw material for food manufacture. 



Scanty depth and high concentration of nutritive material 

 will account for the great production of phytoplankton in Maumee Bay, 

 and the same factors are involved in the diminution of production 

 with increased distance from the river. Since the depth increases and 

 concentration of nutritive material decreases with greater distance 

 from the river, a decline in abundance of phytoplankton is to be 

 expected. 



The average abundance of algae in the three stations in 

 Maumee Bay in 1930 is represented graphically in Figure 18, Curves for 

 albuminoid and free ammonia are included in the graph to show the 

 relationship between concentration of nitrogen in these forms and the 

 abundance of algae. Curves for nitrite and nitrate are not shown 

 because their concentration is not a measure of the amount available for 

 plant use (see page 176) ,<^ Figure 18 shows strikingly the marked re- 

 duction of the ammonias and green and blue-green algae with increasing 



188 



