352 J.E. Hobbieetal. 



TA BLE 8-6 Carbon Budget for Bacteria in Pond B, 1971, Based on Outputs 



% of total 

 g C m yr production 



Outputs 



1. Respiration 



2. Biomass change 



3. Loss to predation 



a. Chironomids 



b. Microbenthos 



4. Methane production 



Gross Production 22.5 100 



Inputs 



1. Total uptake of DOC^ 3.6 16 



2. Hydrolysis^ 18.9 4 



Estimated from total chironomid assimilation and assuming selective ingestion of algae 



over bacteria by a ratio of 2:1. 



Estimated from C kinetic data. 



Estimated by subtraction of total DOC uptake from total production. 



yr~' was produced by bacteria, benthic algae, and micro- and 

 macrobenthic animals. We have made measurements of the respiration of 

 the macrobenthic animals, which make up most of the biomass, and made 

 estimates of the respiration of the algae and of the microbenthos. Overall, 

 the estimate is 4.3 g CO2-C m""^ yr^ for the respiration of the benthic 

 animals plus the algae. The macrobenthos respired 1.5 g C, benthic algae 

 about 1.5 g C (about 10% of primary production), and microbenthos 

 about 1.4 [this is 14% of their biomass of around 100 mg C m"^ and is half 

 of their feeding rate of 28 mg C m~^ day"' (see Microbenthos)]. By 

 subtraction, therefore, the bacteria respired 9.4 g CO2-C m~ yr^ . This 

 appears to be a large quantity but the amount of CO2-C that left the entire 

 pond was estimated to be about 50gC m~^ yr ' (Coyne and Kelley 1974). 

 The remainder is likely root respiration (the sediment respiration 

 measurements were made in the pond center where there were no 

 macrophytes). 



The change in biomass of bacteria over the summer season was 9 g C 

 m ~ ^ yr " ' . Over 99% of this value was attributable to the benthic bacteria. 



Bacteria in the sediments are consumed by microbenthos and 

 chironomids. Fenchel (1975) has estimated the microbenthos (protozoan 

 and micrometazoan) predation in the tundra ponds as 20 mg C m "^ day 

 or 2.0 g C m~^ yr~^ on a seasonal (100 days) basis. Chironomid 

 assimilation of all food was previously noted as 325 mg Cm' day" 

 (Chapter 7). Yet the measured feeding rates were only 7.5 cc sediment 

 m~^ day"'. This 7.5 cc contains only about 1.5 mg bacterial C and 0.75 



