Decomposers, Bacteria, and Microbenthos 369 



TABLE 8-13 Percentage Change in Dark CO^'C Flux in Sediment Cores 

 from Pond A—B Enriched with Inorganic Phosphorus, Ace- 

 tate, or Glucose During 1972, 1973 



The number in parenthesis is the number of replicates. 

 Sediment core mixed; therefore, substrate uniformly distributed. 



Wetzel et al. (1972) by Rich (1970), and by Hargrave (1969). In this same 

 work on Marion Lake, Hargrave found that temperature accounted for 

 71% of the annual variation in oxygen uptake. 



Nutrients 



In these ponds the availability of phosphorus and of labile organic 

 compounds appears to restrict microbial decomposition. This was 

 determined by adding nutrients to the water above the sediments in core 

 tubes; the respiration rates were measured after 4-hr incubations. Most of 

 the experiments involved the addition of phosphate (Table 8-13) which 

 usually increased respiration. Acetate also increased respiration 

 significantly but the variance was high. The results were surprising in view 

 of the large quantities of phosphorus and organic carbon that are present 

 in sediments. However, mere presence does not mean that the nutrients are 

 available. Other workers have also concluded that low levels of nutrients 

 limit decomposition (Waksman et al. 1933, Waksman and Renn 1936, 

 Ryhanen 1968). 



Effect of Animals 



In a number of experiments in other systems, the presence of animals 

 appeared to stimulate benthic respiration. To test if this occurred in the 

 ponds, an 18-day experiment was set up in which the equivalent of 7600 



