102 R. T. Prentki et al. 



a second in late July and early August. There was an additional maximum 

 of ammonia in the melt water from the snow pack. In 1971, the NH3-N 

 was above 100 ^g liter ' from 2 to 5 June and reached 204 ^g liter ' on 5 

 June. It is likely that the NH3 in the snow is easily mobilized by the first 

 water that begins to move through the melting snow (Barsdate and 

 Alexander 1971). The nitrite concentrations are insignificant at all times. 



Most of the nitrogen in Ponds B and C was present as organic 

 nitrogen. In fact, taking mean values for 1970 and 1971, the dissolved 

 organic N (DON) was 89% of the total and the particulate organic N 

 (PON) was 6.8%, about 2 times the concentrations of the dissolved 

 inorganic N. The range of concentration of DON was 800 to 1,400 Mg 

 liter " ' while the PON levels ranged from 30.7 to 1 59.9 ^lg liter " ^ . 



There have been only a few measurements of nitrogen compounds in 

 other arctic waters and these are difficult to compare with the ponds 

 because of the usual build-up of nitrate and ammonia beneath the ice of 

 lakes that do not freeze to the bottom. For example, nearby Ikroavik Lake 

 contained 1,625 ^g NH3-N liter"' and 8.3 ng NO3-N liter ' on 14 June 

 (1970) when the ice still covered the lake. By August, when the lake was ice- 

 free, the surface water contained only 14 ^g NH3-N and 0.0 ^lg NO3-N 

 liter ' which is similar to the ponds at that time of year. Char Lake, in the 

 Canadian Arctic, contained less than 1 to 30 ^g NO3-N and less than 2 ng 

 NH3-N liter ' (Schindler et al. 1974). Particulate nitrogen was higher 

 (mean of 100 Mg PON liter " ' samples) in Ikroavik Lake than in the ponds 

 and Char Lake had 7 to 27 ^g PON liter'. Dissolved organic nitrogen in 

 Ikroavik Lake was similar in concentration (996 ^g N liter ' average for 

 14 samples) to the ponds while values in Char Lake were much lower. 

 Schindler et al. (1974) found an average total dissolved N of 75 ng liter ' 

 so DON is likely around 60 ^g- 



Sediments 



Pond sediments typically contain high amounts of dissolved organic 

 nitrogen (DON) and ammonia but low concentrations of nitrate. For 

 example, in the 4 to 12 cm level of the sediments of Pond J ( 1 1 July 1971), 

 the interstitial water contained 5.6 mg DON liter"'. On 19 June 1971 the 

 1 to 5 cm level of the sediments contained 1 .3 mg DON liter ~ ' . During the 

 winter months, interstitial ammonia concentrations as high as 7 mg 

 NH3-N liter"' were found in the surface 6 cm, but these high values are 

 greatly reduced during the summer in the areas of the beds of rooted 

 aquatic plants. For example, on 20 July 1973 the upper 8 cm of sediments 

 contained only 14 to 75 ng NH3-N liter"' in the Carex and Arctophila 

 beds but from 700 to 2730 Mg N between the beds and in the pond center 

 (Table 4-9). The quantities of NO3-N liter ' in the interstitial water 



