372 J.E. Hobbieetal. 



Chironomid burrows may also allow oxygen to penetrate into the 

 anaerobic zone of the sediments. Some species actually pump water 

 through their burrow; other workers have seen a distinct effect of the 

 burrows on sediment pH and Eh (Edwards 1958, Davis 1974). 



The activities of the macrobenthic organisms may also influence 

 sediment respiration rates by decreasing the size of the detritus particles. 

 Small particles have a much higher bacterial biomass and respiration rate 

 than do large particles (Fenchel 1969, Hargrave 1972). At our research site 

 the highest rates of respiration occurred in ponds with the finest of 

 sediments (X, J, D). 



MICROBENTHOS* 



Introduction 



The general objectives of the pond research, to investigate nutrient 

 cycling and energy flow, led us to approaches that precluded analyses of 

 components of the ecosystem which may well be controlling the 

 microbenthos. Thus, scant attention was paid to predation and 

 competition, to name only two mechanisms. In addition, the microbenthos 

 is a complex but non-functional grouping that in itself includes a large 

 number of species and several complicated food webs. One example is the 

 ciliates, which were studied in some detail but not necessarily because of 

 their importance. It is also true that no one has ever before attempted to 

 analyze the controls of any aquatic microbenthic community so we cannot 

 even make comparisons or gain insights from other studies. 



The sediments of aquatic environments usually sustain a varied and 

 rich microfauna. These animals include protozoans as well as such 

 micrometazoans as turbellarians, nematodes, and crustaceans. Few 

 aquatic studies examine the microbenthos and little is known of its role in 

 the ecosystem. Because of the importance of sediment processes in these 

 tundra ponds, we have attempted to quantify the numbers and production 

 of the microbenthos. A full report on this work is given in Fenchel (1975); 

 data for 1971 and 1972 come from Dillon and Hobbs (1973). 



Methods 



During 1971 and 1972, samples from the sediment of Pond B were 

 fixed in Schaudinn's fluid and diluted, and then subsamples were counted. 

 In 1973, four cores (0.65-cm diameter) were collected to a depth of 6 cm 



*T. Fenchel 



