Decomposers, Bacteria, and Microbenthos 359 



vyater column, in the air, on the sediment surface, and in the sediment to 

 test the effect of mesh size and location. 



Loss of Weight from Macrophyte Detritus 



The green litter incubated under water lost the greatest amount of 

 weight, 37.5%, over the 8-week summer (Table 8-7). Over half of this loss, 

 20.8%, occurred during the first week. This early loss is similar in every 

 way to the initial leaching that takes place in tree leaves placed in water. 

 For example, Kaushik and Hynes (1971) measured some 15% loss in 

 Vlnus leaves after 4 days at 10°C. Much of this leached material is 

 carbohydrate and Chapin et al. (1975) have shown that much of this 

 soluble carbohydrate is retranslocated below ground when the Carex 

 begins to senesce. Thus the yellow leaves should have had less soluble 

 carbohydrate and, indeed, lost only 12.1% in the first week. The summer 

 weight loss from the yellow leaves was 25.5% or 13.4%,after the initial loss; 

 the post-initial loss was similar, therefore, to that from the green and 

 yellow leaves (13.4 vs. 16.7%). In contrast to the green and yellow leaves, 

 the brown leaves lost only 4.9% of their weight over the entire summer. 



From 8 to 58 weeks, which included the winter frozen period, the 

 green litter gained weight (Table 8-7). This gain (4.2% of original weight) 

 is not statistically significant, but the increase was likely due to microbial 

 and microfaunal colonization of the detritus and of the mesh. The yellow 

 fraction lost an additional 9.8% over this 58-week period, and the brown 

 litter lost a highly significant 54.7%. The large loss is presumably a result 

 of the winter freeze-thaw which physically broke up (triturated) the 

 weakened structural material. 



The yellow leaf detritus decomposed slower when buried in the 

 sediments than when placed on the sediments or submerged in the water 

 (Table 8-7); litterbags placed in air lost the least weight of all types (3 to 

 4% over 8 weeks). The leaves placed in 1-mm mesh bags had greater 

 weight loss than those in the 2{)-^im mesh bags, indicating that trituration 

 and subsequent loss may be a significant component of detrital 

 breakdown. Such a breakdown of litter is probably a result both of animal 

 foraging and of breakdown of microfibers by physical forces; the effect 

 would be greatest on the older material which was already weakened. 



Partitioning of Carbon Loss 



The decomposition processes of macrophytes may be separated into 

 leaching, hydrolysis, and trituration. While all of these are operating 

 simultaneously, different stages of decomposition may be characterized by 

 the dominance of a single process. Leaching, as discussed above, is 



