The chemistry, mineralogy, and rates of transport of sediments in the ...

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and velocity (Fig . 1) . For these reasons, Group 3 rivers, and the
Mackenzie at Norman Wells, were excluded from most of the regression
analyses . This group of rivers tends to be rather productive biologically,
and is frequently a migration route for fish (Brunskill et at ., 1973 ;
Hatfield, 1972) .
Comparison of Sediment Transport in the Mackenzie Valley with Other
Subarctic, Arctic, and Temperate Regions .
Table 16 indicates that the large Subarctic and Arctic rivers-(Group
1 in Table 1) of the Mackenzie and Porcupine watershed transport relatively
large amounts of suspended sediment per unit watershed area, compared to
other major North American rivers . This occurs despite 6-7 months of . ice
cover and frozen watersheds during the relatively long winters of the
Mackenzie Valley, compared to year-around open-water flow in some of the
Temperate Zone rivers-listed in Table 16 . This may be the result of less
land stabilization by vegetation in the headwaters of these large rivers
in the Mackenzie Valley, . the presence of degrading permafrost tables, and
relatively great relief inmost of these watersheds .
Corbel (1964) estimated, based largely on precipitation and evapotranspiration,
an average erosion rate of 52 mt kn -2yr-1 for the entire
Mackenzie watershed, which is remarkably-close to our largely measured
estimate of 68 mt km- 2yr-1 (Table 16) . Our Eq . 5, or improvements on
it from more detailed and longer records of data, could be used with
similar equations developed by Jansen and Painter (1974) to estimate
erosion rates for unsampled watersheds in the Mackenzie Valley lowlands .
A separate evaluation of small mountain streams will have to be made,
because Eq .-2-5 do not apply to these types of watersheds . It seems
likely that our Eq . 2-5 will not be of use for predicting sediment or
particulate nutrient transport rates in most other areas - of the North
American Arctic and Subarctic . . The Mackenzie Valley appears to be
somewhat exceptional'' in the relative abundance of trees and higher
vegetation,- a relatively moderate climate, and an abundance of easily
eroded lacustrine and glaciofluviatile sediments in the Mackenzie Valley
lowlands . Most watersheds of the eastern North American Subarctic and
Arctic have a much more severe climate, less vegetation, often less
erodible (or soluble) surface soils, and less' relief .
Table 16 also indicates that the smaller (Group 2) watersheds have
moderate or low rates of transport of sediments, compared to other Arctic,
Subarctic and Temperate zone watersheds . This proportional relationship
between a) watershed area or annual discharge, and b) annual transport
rate found for Mackenzie watersheds is the inverse of the same relationships
found in temperate North American watersheds (see Ritter, 1967) .
According to Ritter, smaller watersheds (Ad .c80 km 2 ) . in temperate regions
of North America have greater-sediment transport rates than larger rivers .
,We emphasize that the smaller watersheds in Group 2 of Table 1 are all in
the Mackenzie lowlands, and do not include any of the numerous mountain streams
in the Nahanni, Mackenzie, Richardson, and British Mountains to the west .