Physics 75 



levels fall throughout the summer and there is no runoff after late June. 

 However, during the wet summer of 1973 the ponds filled again in mid- 

 August and then there were 7 days of runoff. 



Most of the surface of the watershed is standing water for most of the 

 summer. Therefore, the evaporation and evapotranspiration is maximal 

 and the summer precipitation remains in the ponds. The result is that only 

 37% of the annual precipitation leaves as runoff. This is low compared 

 with the 52% measured in a small nearby watershed with well-developed 

 streams or compared with the 70 to 85% measured in other arctic 

 watersheds. The evaporation measured in a 25-cm-deep, 1.21-m-diameter 

 pan at the edge of the pond was 26.6 cm in 1972 and 17.4 cm in 1973. By 

 our calculations, the water level increase should have been 1 .9 cm but there 

 was no actual change in the level. 



The light extinction coefficients ranged from 6.75 to 2.1 in the ponds 

 which means that 26 to 66% of the surface light reaches 20 cm. The strong 

 absorption of light is caused mostly by the humic compounds dissolved in 

 the water. In the sediments, all of the light was absorbed in the top 3 mm. 



Water currents in the ponds increased during periods of higher than 

 normal winds but overall the currents were low. In part, this is caused by 

 the rapid decrease of wind speed close to the pond surface. Also, the short 

 fetch did not allow waves to build to any size. On a number of dates, the 

 wind, measured at a height of 9 m, continued throughout the night but 

 there was no surface water current at all due to an inversion. 



