Decomposers, Bacteria, and Microbenthos 385 



decomposition of detritus. Warmer temperatures would increase bacterial 

 growth but it is doubtful if the high rates could continue for very long 

 before the substrate (detritus) was used up. Therefore, temperature is a 

 control but the low temperatures help to keep the close balance between 

 input and decomposition. One stimulus to bacterial production is grazing 

 by animals. The mechanism for this effect is unknown but may be the 

 result of a constant removal, keeping the bacteria in an active growth stage. 

 Bacteria in these ponds are likely inactive for most of their existence. 

 This is an excellent life-strategy as it allows a large number of bacteria to 

 exist and to be ready to quickly take advantage of good growth conditions. 



Fungi 



A single measurement in 1978 showed 998 m of hyphae (gram dry 

 weight) " ^ at 1 to 2 cm of depth in the sediment of Pond C and 140 m at 

 6 to 7 cm. This is slightly lower than amounts in terrestrial soils at Barrow 

 and much less than amounts in forest soils. The total quantity of hyphae 

 in Pond C is 3500 mg C m ~", which is 70% of the total microbial carbon 

 (taking bacterial biomass as 1 500 mg C m " ^). 



Decomposition and Respiration 



Leaves of Carex were incubated in nylon mesh litterbags in the 

 ponds. Fresh green leaves lost nearly 40% of their weight during the 8- 

 week summer; half the loss occurred in the first week so was likely due to 

 leaching. Yellow leaves had died at the end of the previous summer and so 

 were already leached; they lost 25% of their weight over the summer. 

 Finally, brown leaves had been dead for at least one entire season; they lost 

 only 5% of their weight over the entire summer. Over the winter, the green 

 and yellow leaves did not change appreciably but the weakened brown 

 leaves broke up so that 60% was lost. 



Based on the litterbag measurements, a description of the 

 decomposition can be constructed. If 32 g C of Carex leaves enters the 

 pond at the beginning of the first summer, it will take 4 years to 

 decompose. The leaves start as 33% green and 67% yellow. By the end of 

 the first summer, 9.4 g C is lost (green loses 4 g and yellow loses 5.4 g). At 

 the start of the second summer, there is 22.7 g C present, all brown. At the 

 start of the third summer, there is 18.9 g C, and at the start of the fourth, 

 7.7 g C. Over the 4 years, most of the leaves are lost by mechanical 

 breakdown (18.8 g C), while 8.1 g C is lost by leaching as DOC and 5.2 g C 

 lost by hydrolysis (enzymatic breakdown). Our measurements were not 

 accurate enough to tell whether or not a small amount (5 or 10%) was 

 being preserved in the sediments. In addition to the 32 g C of Carex litter 



