342 J. E. Hobbieetal. 



0400 0800 



Time, hr 

 1200 1600 2000 



2400 



FIGURE 8-2. Numbers of bacteria at various depths 

 over 24 hours in the plankton of Pond A on 24 July 

 1973. 



biomass; the maximum quantity was 2.6 g C m "^ and the average was half 

 that (assuming 5-cm depth of sediment). 



Comparison of these values for cell density and biomass with other 

 studies is difficult because of the variety of methods that have been used. 

 The most common methods currently in use are plate count procedures 

 and direct counts utilizing one of a variety of stains. Platecount techniques 

 do not work for the determination of numbers and biomass; for example, 

 Francisco (1970) reported a ratio of direct to plate counts ranging from 21 

 to 8900 with no apparent explanation for the differences. There are also 

 smaller differences among the various direct count techniques but recent! 

 improvements in the microscope systems and in the membrane filter, have 

 led to agreement among a number of techniques with fluorescent dyes 

 (acridine orange, FITC) and methods based on the scanning electron 

 microscope (Bowden 1977) and lipopolysaccharide content of the bacterial 

 cell wall (Watson et al. 1977). 



The numbers of bacteria found in the tundra ponds agree with other 

 measurements made in temperate waters with acridine orange (Table 8-2) 

 but are higher than numbers collected with other methods, such as the 

 phase contrast plus erythrosin dye. The difference is caused by better 

 visibility with acridine orange or FITC that allows very small bacteria to 

 be seen. As already noted, the high numbers in the ponds are caused, in 

 part, by resuspension from the sediments. Even so, there are always high 

 numbers of bacteria in both eutrophic and oligotrophic waters. The range 



