Site C. This is a small shallow tundra pool that is floored with a layer of fine-grained, water- 

 sorted particles with an abundance of vegetative detritus. Both emergent and floating aquatic 

 plant species were present. 



Site D. This is another small tundra pool very close to site C, but supportinj^ an entirely 

 different set of aquatic plant species. This pond has a very prominent blue-green ilgal mat on the 

 bottom. 



Site C. This is a characteristic alpine site weU above the shrub tundra. The soil is rich with 

 humus and moisture, but here and there it is interrupted by natural disturbances producing very 

 different habitats and therefore supporting a variety of tundra plant species. There is very little 

 overlap of species distribution between this site and those below. 



Site F. This is a kettle pond which is now shallow and probably dependent upon surface 

 runoff to maintain even its present level. The upper portion of its steep sides is covered with the 

 same species as compose the surrounding tundra. The lower area supports an entirely different 

 assemblage. The floor of the kettle has emergent and submerged aquatic plant species. 



Plants in each study site were tagged, herbarium specimens taken, in situ photographs taken, 

 and sketches prepared. The plants were then removed and set up for nitrogen fixation testing as 

 described in the Barrow section of the report. Acetylene-reduction was the principal method used, 

 with back-up nitrc^en fixation tests using nitrogen-15. Pond water samples were tested both 

 unconcentrated and concentrated through a 10-micron screen in a plankton concentrata. Incubation 

 was carried out under conditions closely approximating natural. A fuU range of blanks and controls 

 was included. Representative lichens from each site were collected and tested similarly for nitrogen 

 fixation. 



The results shown on table XLVIII indicate nitrogen fixing activity associated with a variety 

 of plants. Table XLIX is a list of plants showing no acelylene reduction activity. Several lichens, 

 all belonging to groups with blue-green algae as the algal phycobiot, appear to be major contributors 

 to the nitrogen budget. Blue-green algae from the tundra and tundra ponds are also extremely active 

 nitrogen fixers. Oxytopis, a legume, also showed high rates of acetylene reduction. Dryas in site 

 A also reduced acetylene, althoi^h the rate was low. On a unit biomass basis, the lichens and 

 blue-green algae are by far the most effective, when the relatively small plant size tested is taken 

 into account. 



The ubiquity of nitrogen fixation at pond site C and the low rates suggest that perhaps blue- 

 green algae attached to the plants in small numbers may be responsible. The results of the nitrogen 

 15 work will help in interpreting these results. The high sensitivity of the acetylene reduction 

 method results in positive results where small numbers of contaminants are included in the sample. 

 On the otherhand, the frequent appearance of Carex sp. in connection with positive results requires 

 further investigation. Similarly, the positive results associated with Sparganium miniumu at 

 site D are surprising. 



Analysis of these results on a site by site basis suggests that nitrogen fixation is important 

 on exposed wind-strained ridges, where soil buildup is very limited (site A). A lower, well-vege- 

 tated area (site B) had fewer nitrogen fixing components. However, even in such an area, the 

 extent of nitrogen fixation of lichen cover under the taller vegetation could be considerable. In 

 the aquatic environments, nitrogen fixation appears to he an important input. 



At this point, it is not possible to estimate the percentage of the daily nitrogen input with 

 tundra plants supplied by nitrogen fixation. The information obtained during tliis summer suggests 

 that it is a very significant proportion in some of the environments. Since blue-green algae steadily 

 release ammonia and aganic nitrogen compounds within the environment, these at least may provide 

 the nitrogen source for other contiguous plants. 



119 



