Decomposers, Bacteria, and Microbenthos 341 



TABLE 8-1 Numbers of Bacteria at Different Depths in the Sediment 

 of Pond B, Subpond 6, on 7 August 1972 



Depth 



10^ '^ ceUs(gdry wt) ^ 



1 cm 



2 cm 



3 cm 



4 cm 



5 cm 



5.8 ±0.7 



3.3 ±0.7 

 2.5 ±0.2 



1.4 ±0.2 

 0.8 ±0.3 



variability from day to day, and even from hour to hour, in the numbers of 

 bacteria. This was caused by wind-driven currents that resuspended the 

 bacteria from the sediment up into the water column of these shallow 

 ponds. For example, on 24 July 1973 the bacteria in Pond A were sampled 

 over a 20-hr period (Figure 8-2) during which the wind increased until 

 early afternoon and then decreased through the rest of the sampling 

 period. Wind mixing of the water column and sediment resuspension did 

 appear to cause vertical movement of the bacteria (Figure 8-2). A similar 

 experiment on 12 to 13 August 1974, when the wind was steady, showed 

 little vertical movement over a 28-hr period (Hobbie and Rublee 1974). 



Carbon in the bacteria was calculated from cell counts using a 

 conversion factor of 0.87x 10"^ /ig C per cell (Ferguson and Rublee 1976). 

 Peak biomass in the water column was generally 5 mg C m '. As with cell 

 counts, sediment bacterial biomass was significantly higher than plankton 



7.0 



6.0 



5.0 



E 4.0 





2.0 



1.0 



Plankton) 

 Pond C 



20 

 Jun 



10 



20 



Jul 



7.0 



6.0 



5.0 



4.0 -5 



a> 



3.0 - 



V 



o 

 2.0 o 



- 1.0 



10 



Aug 



FIGURE 8-1. Numbers of bacteria in the sediment of Pond A and the 

 plankton of Pond C, 1973. 



