THE DIRTRIBUTIOX OF BACTERIA IN LAKES 



57 



follow closely the curve for total plankton, 

 but witli a lag whieli is greater in the case 

 of tiie i^late counts. There were three 

 plankton pulses — a spring and autumn 

 growtli of diatoms and a midsuunner growth 

 of blue-green algae. There are also three 

 peaks to the curves for bacteria. 



It was previously noted that periphytic 

 bacteria were more numerous on slides sus- 

 pended in the upper layers of Lake Alex- 

 ander during the period of blooming, i.e., 

 August. The data presented in Fig. 3 were 

 all colleeted from the surface. Table VIII 

 shows liotli vertical and seasonal variations 



fluctuations of llic pci-iphytic badci-ia in 

 Lake Mendota. It was previousl\- noted 

 that the summer stratification of this lake 

 is not sufficiently sharp to affect obviously 

 the vertical distribution of the bacteria. 

 Under the ice in winter the bactei-ia are 

 uniformly few in number until the bottom 

 meter is reached, where they show an amaz- 

 ing increase. Noted in three successive 

 observations, this must be significant. 

 After the ice went out and the lake warmed 

 up, the bacteria increased in number and 

 became rather uniformly distributed from 

 top to bottom. 



TABLE VIII 



Distribution of Periphytic Bacteria by Depth and Season, Lake Alexander.* 



Numbers of Bacteria Per sq. mii Per Day Deposited upon Submerged Slides. 



Dates Are Median Dates of Period of Immersion. 



1933 



* All observations at Station 1. 



at Station 1. It will be seen that, although 

 there are some anomalous counts, the verti- 

 cal distribution remains fairly uniform 

 throughout the year, except during August 

 Avhen distinctly higher counts occur at the 

 surface. It will be noted that at all levels 

 the counts are lower during early spring 

 and late autumn, when the temperature was 

 lower. 



Table IX shows seasonal fluctuations of 

 the periphytic bacteria at the various lit- 

 toral stations in Lake Alexander. It is 

 found that the bacteria do not fluctuate 

 with the seasons so extensively as do those 

 in the open water station. There is, how- 

 ever, a tendency for the bacteria to be de- 

 creased in numbers as the water cools in the 

 autumn. 



Table X shows both vertical and seasonal 



AYe have as yet no adequate data on sea- 

 sonal fluctuations of bacteria in the bottom 

 deposits. Williams and McCoy (1935) 

 noted only minor differences in samples 

 from Lake IMendota taken during the win- 

 ter and during the summer. Karsinkin and 

 Kusnetzow (1931), using a modification of 

 Winogradsky 's method for the direct micro- 

 scopic examination of soil, found that the 

 bacteria in the bottom deposit increased 

 progressively from May to September. The 

 author considers this method entirely unre- 

 liable as a quantitative procedure. Speran- 

 skaja (1935) found that the bottom deposits 

 of the Russian lakes increased in their con- 

 tent of nitrogen, sugar, hemicelluloses, and 

 cellulose in the autumn, and that these sub- 

 stances decreased during winter stagnation. 

 Kusnetzow and Kusnetzowa (1935) consid- 



