The Soils and Their Nutrients 



239 



1500 



o 



c 1000 



4. 



X 



o 



Barrow, Alaska 



— Predicted Values 

 ■— Field Measurement 



FIGURE 7-10. Comparison of simulated and measured rates of 

 nitrogen fixation at Barrow and at Kevo, Finland. (Bunnell and 

 Alexander, unpubl.) 



perature at which recovery is taking place (Kallio and Alexander, un- 

 publ., Kallio 1973). Rates of nitrogen fixation per unit of ground surface 

 measured for arctic lichens are somewhat higher than those measured in 

 other Biomes (Stewart 1969). 



Inputs of Nitrogen and Phosphorus by Precipitation 



Snowfall includes approximately 30% of the total nitrogen supplied 

 by precipitation. Ammonium is the predominant form of nitrogen found 

 in snowfall (Dugdale and Toetz 1961), aUhough organic nitrogen has not 

 been measured. The fraction of the inorganic nitrogen present as nitrate 



