melting ice wedges and soils and tundra which are more wet. The degree of thawing and consequent 

 subsidence depends upon the amount and type of ice contained in the permafrost beneath the track. 

 Melting of ice wedges results in small ponds. If the track is on a slope or intercepts a drainage 

 channel, it is susceptible to erosion, as is dramatically indicated by the effects seen on the re- 

 search sites at Barrow. 



The study of an old track at site 3 was undertaken in an attempt to determine some of the 

 dynamic interactions which persist some time after the original disturbance. The track was occa- 

 sionaUy used in summers during the mid 1960's. Its features varied depending upon the type of micro- 

 relief and substrate it crossed. Some places were completely barren of vegetation and others 

 supported some of the most dense vegetative growth seen at Barrow. Characteristic of most of the 

 track, however, was an absence of standing dead vegetation and litter. Thus, it appears that the 

 turnover of nutrient in this situation must be high and presumably is unassociated with higher 

 activities and/ or populations of decomposing microorganisms. 



Three plots were established across the track, each showing different degrees of erosion and 

 wetness. Plot 306 was relatively dry and disturbance was least conspicuous. Plot 303 was 

 intermediate in wetness and slightly depressed. Plot 305 had considerable subsidence due to ground 

 ice melting and had surface water on it throughout the summer. Four points across the track were 

 sampled in each plot: in the track depression, on the mound between the two tracks, on the outer 

 edge of the track or bank, and at a control point several meters from the edge (Fig. 24, 25). 



Microrelief, soil morphology, plant and soil nutrients, primary production, thaw, soil moisture, 

 redox potentials and insect and microbial activities were measured at these plot points periodically 

 throughout the summer. The following reports the differences encountered within and between each 

 transect on the track. •^ 



Over the entire summer season, soil temperatures along the cross-sectional transects were, in 

 decreasing order, nround > depression > bank > control. The depth of thaw was more than double that 

 of the control beneath the weasel tracks and the intervening mound where the track crossed a wet 

 area (plot 305). Thaw differences in the drier plot 306 were neglibible and were intermediate across 

 plot 303. On the average, thaw along cross-sectional transects was, in decreasing order, 

 mound > depression > bank > control (Table XXVII). 



The average pH of solution extracted from the upper 10 cm of soil on 2 July was 7.1 in the 

 depressions, 7.0 in the nraunds, 6.9 in the banks, and 6.5 in the controls. In general, soil solution 

 pH of plot 305 control was about neutral (6.8 to 7.1) while those of plot 303 and 306 controls were 

 slightly acid (5.8 to 6.7). Soil solution pH of the depressions and mounds of plots 303 and 306 

 was slightly less acid than that of the controls, but that of plot 305 had higher pH values in the 

 depressions and mound (7.4 to 8.1). The reasons for the high pH values of the latter are not evident 

 at this time. It is possible that bases were added to wetter depressed areas of the track by surface 

 water moving in from the surrounding area. 



Measurements of the redox potential corrected to pH 6.0 confirmed that plot 306 was the driest 

 plot and 305 the wettest plot. Redox values (Eh at pH 6.0) at plot 306 ranged from ^82 to +132; at 

 plot 303, from 146 to tlOO; and at plot 305, from -181 to +89. Thus the soil of plot 305 had the 

 greatest reducing conditions while that of plot 306 had the least. On the average, tlie greatest re- 

 ducing conditions were in the track depressions with little difference between the other three 

 locations. 



The respiration rate of soil taken from the center of the track was approximately twice the rate 

 of uncompacted soil on control areas at site 3. For example, the respiration rates of the to 2-cm 

 surface soil of the control and of the track were 10.5 and 23.8 n liter Oj/hr g dry soil wt, respectively, 

 on 3 July. There were fewer bacteria and fungi in the track soil than in the control. However, this 

 may simply reflect the fact that these microorganisms were more actively decomposing a smaller 



67 



