Evaluation of Historical Sediment Deposition 



core also were visible in the same relative 

 location in other cores collected from the same 

 lake. Since no banding was observed in cores 

 collected from Swan Lake, visual cross-com- 

 parisons between cores was not possible. 



It is important to note that the present analy- 

 ses were not designed for quantitative estab- 

 lishment of whole-lake sediment budgets over 

 the last 150 years. Thus the study results should 

 not be used to estimate the total sediment load- 

 ing to the study lakes over the period of record. 

 Such analyses would require analyses of a 

 number of cores collected from various parts of 

 each lake. Rather, the present analysis simply 

 utilized the stable deep-lake sediments as a 

 continuous monitor of relative changes in depo- 

 sition of fine sediment from the watershed to the 

 lake environment. Thus, the absolute sedimen- 

 tation rates are of less interest that the relative 

 change in these rates over time. 



Results and Discussion 



Whitefish Lake 



The Whitefish Lake catchment has been 

 subject to a number of land disturbance activi- 

 ties (both man-induced and natural) which may 

 have influenced the sedimentation rate in this 

 lake. I assembled a history of major land distur- 

 bance activities in the catchment, including 

 natural and human-related activities. These 

 various activities will be chronologically com- 

 pared with the lake sedimentation rates for 

 evaluation of potential causal relationships. 



Natural Disturbances 



There were four years in which fires burned 

 500 acres or more in the watershed during the 



period of record. The greatest acreage burned 

 in 1910, when 5562 acres burned, representing 

 6.7% of the total watershed area. 



Data collected in this study do not show 

 evidence of large changes in lake sedimentation 

 following any of these fires (Figure B-1). The 

 sedimentation rate did increase during the time 

 interval of the 1910 fire, and some of this in- 

 crease may have been attributed to fire. How- 

 ever, human land activities (described later) 

 also occurred in the basin at this time; thus 

 specific fire effects are difficult to discern. 

 Moreover, no obvious ash layer was visible in 

 the lake core around 1910. The mean sedimen- 

 tation rates shown in Figure B-1 were in the 

 midst of decade-long periods of decline during 

 the time period of two other fires (1919, 1937). 

 Sedimentation rates increased slightly during 

 the period of the 1926 fires; however, extensive 

 human disturbance of the watershed commenc- 

 ing in the late 1920s complicates determination 

 of actual cause and effect. Nevertheless, a thin 

 layer of black ash is clearly visible in the sedi- 

 ment core at a depth corresponding to the time 

 period around 1926. (See photo in complete 

 report.) This distinct ash layer undoubtedly 

 resulted from transport of ash from the 1926 

 fires into the lake (either from the air or via 

 streams). One of the 1926 fires, called the 

 Hellroaring Fire, burned down to the shore of 

 Whitefish Lake, and extended up into the 

 Whitefish Range into the area that subsequently 

 became the Big Mountain Ski Resort. Nonethe- 

 less, changes in the sediment record resulting 

 from the 1926 fire appear short-lived, and of 

 small magnitude, compared to other distur- 

 bance events described later. 



Flooding is another natural disturbance 

 activity which may influence lake sedimenta- 

 tion rates. It is well known that over the course 

 of a given year, the of majority sediments car- 

 ried by Rocky Mountain streams are trans- 

 ported during spring run-off. Thus during 



Flathead Basin Cooperative Program Final Report 



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