The rate of erosion in this channel has been observed on the ground and photogrammetrically 

 since the late 1940's, At that time the stream's base level was lowered as a result of dredging the 

 lagoon into which the stream flows. This, plus several other man-made alterations in the drainage 

 basin, has resulted in accelerated erosion of the channel as the stream seeks a new base level, 

 Headward erosion of the headwall in the period 1964 to 1970 amounted to 125 m (Fig. 3). 



As a result of practically no summer runoff, the rapid erosion of the Footprint Creek headwall 

 was restricted to the period of spring runoff. During 1970, erosion was approximately 10 m of head- 

 wall movement. Of this amount, 3 to 4 m occurred after spring runoff as slumping of the undercut 

 headwall. The entire period of spring breakup, runoff, and erosion at this headwall was obtained 

 on color, time-lapse movie and is available from USA CRREL. This movie shows interesting 

 seasonal and diurnal features of the early summer runoff and erosion. 



On 12 July 1970, at the end of the spring runoff period six stations were sampled along Foot- 

 print Creek, three above and three below the headwall (Fig. 3). Particulate solids, turbidity (in 

 Jackson Turbidity Units), pH, alkalinity, other chemical data along with '*C primary productivity 

 and chlorophyll contents were determined and are presented in Table XXIX. 



Substantial quantities of dissolved and particulate substances are introduced into the water at 

 the headwall. In large part, these substances leave the water a relatively short distance downstream 

 from the principal site of disturbance. Planktonic and benthic primary productivities are severely 

 depressed at the headwall but rise to unusually high values further downstream. 



The thermokarst pond G lies in an area of upland tundra with well-developed high-center poly- 

 gonized ground lying about 500 m west of the IBP pond site 7. A tracked vehicle trail which was 

 used extensively in the early 1960's follows the troughs of the polygons up onto the higher ground. 

 At the transition from low to high ground, ice-wedge melting was induced by the track disturbance 

 and pond G was formed. The margins of this pond are unstable, and continuing erosion results in 

 a distinct turbidity in the water. 



While it was not possible to initiate a comprehensive study of pond G, it was sampled twice 

 during the 1970 field season on 11 July and 28 August. On the first sampling date, the water was 

 thermally stratified, probably due to clear sky conditions and low wind velocity in combination with 

 high water color and turbidity, factors which tend to restrict heating to the uppermost layers. From 

 the available data, it appears that the phosphoms nutrients are quite abundant and tliat plankton 

 primary productivity is depressed in comparison with undisturbed tundra ponds. 



73 



