106 R. T. Prentki et al. 



TABLE 4-1 1 Concentration of Inorganic Nitrogen Compounds 

 in Summer Precipitation at Barrow, A laska 



Date NH3 NO3 NO2 



Rain (Dugdale and Toetz 1961) 



*Data are expressed as fig N liter ^ . 



Budget 



The additions and losses of nitrogen to a pond are the sum of nitrogen 

 fixation, nitrogen added in summer rainfall, nitrogen added in spring 

 runoff, and nitrogen lost in denitrification. 



The inorganic nitrogen in the summer precipitation at Barrow has 

 been measured by three different projects (Table 4-1 1). We have also made 

 several measurements of DON that average 60 ^g N liter '. During the 

 summer of 1971, the precipitation was 4.1 cm. Taking the overall means 

 from Table 4-1 1 and the DON value, the total input in rain of dissolved 

 inorganic nitrogen (or DIN) was 1 1 .5 mg N m "^ yr " ', while the input of 

 DON was 2.46 mg N m^^ yr^- The ammonia concentrations, which 

 make up 91% of the total DIN input in rain, are similar to those reported 

 by Junge (1958) for various locations within the U.S. In contrast, 

 precipitation at the Hubbard Brook Experimental Forest, New 

 Hampshire, contained nitrate as the most abundant DIN form (76-87% of 

 the total DIN)(Fisher et al. 1968). The nitrate in rain was 50 times higher 

 at Hubbard Brook than at Barrow and the rainfall was 10 times higher. 

 The net result was that the input at Hubbard Brook was 880 mg N in 1964- 

 65 and 2090 mg N m "Mn 1965-66. 



Another possible source of nitrogen is from seepage of water from the 

 pond drainage basin. This is potentially important as there is a high 

 concentration of DON in the tundra soil. However, as discussed in 

 Chapter 3, the drop in water level matches the evaporative water loss fairly 

 well and other experiments indicate that there is very little percolation or 



