46 J. E. Hobbie 



feces are deposited in the troughs and in this way the nutrients from many 

 habitats are actually concentrated in the troughs. This concentration may 

 contribute to the higher soil nutrients (especially phosphorus) found in the 

 troughs which in turn may contribute to the higher rates of production and 

 decomposition found in these areas. 



Some of the same hypotheses came out of a study of the entire 

 nitrogen budget (Barsdate and Alexander 1975). Nitrogen fixation was the 

 most important input; precipitation was only one-third as great (Figure 2- 

 8). The outputs were very small, with denitrification and runoff of organics 

 and ammonia the major losses. Most of the input (65%) was stored. Thus, 

 the system conserves its nitrogen (nitrogen appears to accumulate), and 

 microorganisms (here, nitrogen-fixing algae) are important in controlling 

 flux rates of nutrients and may well control the entire production rate. 



In conclusion, the terrestrial ecosystem of the tundra is rich in total 

 nutrients and energy but poor in amounts actually available and 

 circulating. The activity of decomposers regulates the system. 



SUMMARY 



The Tundra Biome was one of five ecosystems studied in the U.S. 

 unddV the International Biological Program. Both a terrestrial and an 

 aquatic study were carried out at Barrow, Alaska, with the goals of 

 developing an understanding of the ecology through measurements of the 

 flux of carbon, nitrogen, and phosphorus through the ecosystem. 

 Mathematical modeling was one of the tools to be used; the needs of this 

 effort meant that much experimental work had to be carried out to define 

 the interrelationships of the processes with an environment and to define 

 the controls that were operating. In the aquatic project, whole ponds were 

 fertilized with phosphate and nitrogen and one pond was treated with 

 crude oil. 



Past studies of arctic lakes and ponds have been largely descriptive. 

 Only the present study, several previous studies at Barrow, and a 

 Canadian IBP study have dealt with the dynamics of the ecosystems. 

 Arctic lakes and ponds seldom warm above lO'C, are usually unstratified 

 during the summer, and are covered with a 1- to 2-m-thick ice sheet for 9 

 to 10 months of the year. Ponds and shallow lakes usually freeze solid. 

 Because much of the total water in lakes and ponds is meltwater from 

 snow, the concentration of ions is low. There is some interaction with the 

 soil so that areas that have calcareous bedrock will contain streams and 

 lakes with relatively high ionic content, but the permafrost prevents much 

 movement of water in and out of the soils. As a result of the low quantities 

 of ions, and of the relative purity of the precipitation, the nutrient 

 concentrations are low and the lakes and ponds are oligotrophic. 



