Macrobenthos 



327 



1973. Thus, individuals in North Meadow Lake were the smallest at 7 mm, 

 those in North Meadow Pond the largest at an estimated 20 mm. Animals 

 from several small, shallow inland ponds near Ikroavik Lake on 26 July, 

 1973, were very large for that date, 16 to 18 mm. 



The size of the animals when they first appear on the surface of the 

 sediments and the maximum size attained during the summer vary 

 inversely with the depth and volume of the pond or lake. Accordingly, 

 North Meadow Lake was 100+ cm deep; Pond A, 25 cm; North Meadow 

 Pond, 10 cm; and Ikroavik Lake Ponds, 6 to 10 cm. The reason for this 

 relationship is that the temperature on warm sunny days is higher in 

 shallow ponds than in deeper ponds and lakes. For example, the 

 cumulative degree hours above 10°C in 1972 in Pond C, which is 

 equivalent to Pond A, was 2.4 times greater than the degree hours in 

 North Meadow Lake by September (Figure 7-13). Similarly, Stross and 

 Kangas (1969) measured twice as many degree days in a trough pond (0.5 

 m maximum depth) as in Imikpuk Lake (maximum depth 2.8 m). 



The greatest differences in temperature in various habitats occurred 

 in early summer when insolation was highest. At this time, most of the 

 light energy received at the lake surface is reflected or goes to melting ice 

 (Figure 2-4). The ponds, in contrast to the lakes, thaw early because of 

 their thin ice cover and become warmer much sooner than the lakes. Thus, 

 Lepidurus in shallow ponds have an earlier hatching date and, depending 

 upon June temperatures, a faster initial growth rate than in lakes. 



V 70- 



E 



o 



N 

 O 



o 

 (T 



c 

 o 



Ml 



30 



35 



5 10 15 20 25 



Organism Total Length, mm 



FIGURE 7-14. Respiration of Lepidurus arcticus at 

 four temperatures. 



