356 J.E. Hobbieetal. 



decomposition of organic matter in the ponds must also be in a rough 

 steady state at the present time. An increase in temperature would increase 

 the decomposition rate and upset this balance so that eventually the 

 process would run out of substrates. Again, the low temperatures are a 

 control but the rate of supply is the most important control. Another bit of 

 evidence for this comes from the study of Morgan and Kalff (1972) on 

 Char Lake, an unpolluted arctic lake, and on nearby Meretta Lake, which 

 receives sewage. Despite the similar water temperatures, the bacterial 

 activity was much higher in Meretta than in Char Lake. 



Another control that has been suggested is animal grazing. Hargrave 

 (1970) reported that bacterial activity in grazed systems was generally 

 higher than activity in ungrazed systems. Some experiments carried out at 

 Barrow with Carex for a substrate indicated that phosphorus cycled much 

 more rapidly in microcosms where protozoans were present than in 

 microcosms without protozoans (Barsdate et al. 1974). In a different 

 study, Fenchel (1977) found that barley straw decomposed more 

 completely (80%) when protozoa were present than when bacteria alone 

 were present (20%). The phosphorus experiments showed that the 

 enhancement of activity did not come from release of PO4 by the animals. 

 Although other nutrients could have affected the microbes, it is more 

 likely that the grazing removed inactive cells and somehow kept the 

 population active. Thus, the "grazing effect" does occur in the Barrow 

 ponds but to an unknown degree. 



FUNGI 



Hyphal Length and Biomass 



The species and biomass of the fungi in the terrestrial soils at Barrow 

 were intensively studied during the IBP project (Bunnell et al. 1980). Most 

 of the fungal biomass was hyphae; these were measured by direct counts 

 with the light microscope. The average amounts of hyphae ranged from 

 496 to 1445 meters per gram dry weight of soil. Although this appears to 

 be a large amount, woodland soils usually contain about 7000 m (gdw) 

 Most of the hyphae in the Barrow soils are in the top 7 cm and their total 

 mass is around 4 g m ^ Bunnell et al. (1980) point out that 75% of the 

 microbial biomass in this habitat is bacterial. 



The amount of hyphae in the pond sediments was measured on 29 

 July 1978 by Gary A. Laursen (personal communication) with the same 

 techniques used in the terrestrial study. He found that sediments of Pond 

 Omega (Miller et al. 1978) contained 1662 m (gdw) "' at 1-2 cm and 296 m 

 (gdw)"' at 6-7 cm. Sediments in Pond C contained 998 m and 140 m 

 (gdw) " ' at the same depths. 



