54 



PROBLEMS OF LAKE BIOLOGY 



tails and sedges. Station 3 is a similar lit- 

 toral station, but somewhat different in 

 character. Here the bottom is carpeted 

 with Cliara, and wild rice is the dominant 

 emergent plant. The bottom here is almost 

 pure marl. Station 4 is a shallow sheltered 

 lagoon so choked with aquatic plants (pond 

 lilies, Potamogetons, Elodea, Myrioplnjlluni, 

 etc.) that a boat is pushed through with dif- 

 ficulty. Station 5 was chosen as transi- 

 tional between the sheltered littoral stations 

 and the open lake. Here the water is about 

 2 meters deep. The bottom is covered by 

 CeratophyUnm, but there are no emergent 

 plants. Station 6 was chosen as an exposed 

 littoral station. Here the bottom is made 

 of boulders covered with CladopJiora and 

 Rivularia. 



TABLE VI 



Horizontal Distribution of Bacteria in Lake 

 Alexander. 



* Bacteria per square mm per day deposited upon 

 submerged slides. 



t Bacteria per cc of surface water. 



t Bacteria per cc of bottom deposit, from surface 

 of bottom. 



Table VI shows the results of counts of 

 bacteria from these seven stations. In most 

 of the shallow water stations slides were 

 submerged only at the surface. For com- 

 parison, therefore, only surface data from 

 the other stations are presented, and the 

 results of plate counts are also based only 

 on surface samples. The table presents the 

 averages of a number of observations made 

 from May to October, inclusive. 



A study of this table shows, first, a fairly 

 close parallelism between the three sets of 

 data ; the shoreward distribution of bacteria 

 in the water, or in the mud, or growing upon 



submerged surfaces, appears to be affected 

 in the same way. It will be noted that the 

 three protected littoral stations with abun- 

 dant aquatic plants show very high counts, 

 especially of periphj'tic bacteria. The ex- 

 posed littoral station (6) shows counts only 

 slightly higher than the open water stations. 

 The transitional station (5) resembles the 

 open lake as regards the peripliytic bacteria, 

 but is similar to the sheltered bays as re- 

 gards the plate counts. 



Probably the most important factor de- 

 termining the shoreward distribution of the 

 bacteria is the occurrence of aquatic plants. 

 Where these are abundant, bacteria are nu- 

 merous. Mere shallowness of the water is 

 not an important factor. It is probable 

 that the increase of bacteria in the vicinity 

 of larger aquatic plants is due to larger 

 amounts of dissolved organic matter in the 

 water, derived from these plants. And it 

 is probable that the surface provided by 

 these plants is also a factor. The marked 

 increase in the bacteria of the bottom de- 

 posit in the sheltered littoral stations is also 

 due to the larger amount of organic matter 

 provided by the rooted plants. The bottom 

 deposit in these stations is a coarse, fibrous 

 material made up largely of plant remains. 



Table I shows the results of the transect 

 made in 1934. The shore at Station A is 

 a wave-swept sandy beach. Beginning at a 

 depth of about one meter, there occur some 

 rooted plants which increase in size and 

 abundance with increased depth. These 

 are mainlj- Potamogetons, but towards 

 deeper water there occurs an extensive bed 

 of Ccratophijllum. This probably extends 

 to a depth of 6 or 7 meters. 



Stations were established at each one 

 meter contour line, and slides were fastened 

 at each meter of depth. The results are a 

 little irregular, but certain tendencies are 

 apparent. The bacteria were deposited on 

 the slides in larger numbers at or near the 

 surface throughout the deeper part of the 

 lake. This is again to be attributed to the 

 occurrence of floating blue-green algae. The 

 lake was blooming during the period of ob- 

 servation. Further, the bacteria are more 

 abundant on the slides suspended in the 



