306 M. Butler etal. 



Sediments in stands of plants along the shore support a fauna similar 

 to that in peaty sediments in pond centers, but in addition have a number 

 of Orthocladiinae {Psectrocladius, Cricotopus). Larval samples along 

 transects in Pond J in 1971 showed a trend toward smaller sizes at the 

 edges. Chironomids in the Carex beds averaged 0.14 mg dry weight, with a 

 range of 0.06 to 0.26 mg, while those in the center ranged from 0.23 to 0.58 

 mg and had a mean of 0.46. Qualitative samples in 1975 indicated that size 

 differences corresponded to species differences, with many Cricotopus, 

 Psectrocladius, Corynoneura and Tanytarsini in the shallows but many 

 large Chironomus in the pond center. 



The boundary between aquatic and semiterrestrial marsh habitats is 

 sometimes sharp, as when the pond bank is slightly undercut by erosion, 

 but more often the shallows grade smoothly into wet tundra which is 

 submerged just after snow melt but dries early in the summer. By the end 

 of summer in dry years, the shallower ponds dry out completely and the 

 sediments crack. In most years the Carex stands are no longer in standing 

 water by freezeup time. Emergence traps placed near the edges of Carex 

 beds caught a greater proportion of Orthocladiinae in the genera 

 Limnophyes , Pseudosmittia, Lapposmittia, and Metriocnemus, all 

 suggestive of semiterrestrial habitats. 



Species 



All quantitative estimates of benthic populations were made in pond 

 centers, where the most important species by biomass or production were 

 those in the genus Chironomus. C. hyperboreus, reported to be dominant 

 in arctic and subarctic ponds (Andersen 1946; Lindegaard and Jonasson 

 1975), occurred in the area but was rare in the larger ponds at Barrow. It 

 appeared to be most common in the smaller ice-wedge ponds and in 

 flooded grassy areas which dried out in late summer. 



The most common Chironomus in the ponds was reared in the 

 laboratory and many adults were available for comparison, but the range 

 of morphological features did not match any known species precisely. C 

 pilicornis (Townes) was described from Barrow material, and was nearest 

 the dominant Chironomus in pond centers, so we have used that name 

 here. Details of size, the shape of the superior volsella and antennal ratios 

 differed between Chironomus collected in early and late July, and 

 emergence periods were distinct for the two forms. Larval chromosomes 

 have not been compared so we do not know whether these two are distinct 

 from each other, or whether one or two new species is involved. The other 

 common species of Chironomus, C riparius, was identifiable as larvae and 

 adults. 



Tanytarsus gregarius gr. sp. 2 is definitely a new species. The male 

 genitalia place it in the T. gregarius group (Reiss and Fittkau 1971), but its 



