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

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d
In areas of greater relief (or with high values of b, see Table 2)
streams and rivers likely scour their beds with great energy, and bedload
transport will be an important component of the total sediment load
(Nanson, 1974 ; Balster and Parsons, 1968) . In the mountainous headwaters
of the Arctic Red River, Twisty Creek carries 502 of its total sediment
load as bedload (Jasper, 1974) .
Reactivity of Suspended and Bottom Sediments
The low cation exchange capacity of suspended and bottom sediments of
Mackenzie Valley rivers (Table 5) is in the expected, range for the relatively
simple clay minerals illite and chlorite (Grim, 1968 ; p . 189) which
are found in nearly all samples . These values are similar to those found
by Allan et at . (1969) for poorly-drained interior Alaskan soils . Even
with these relatively low exchange capacities, the mass of elements that
can potentially be exchanged from particulate phase to the solution phase
(usually caused by a change in solution chemistry, such as Mackenzie waters
mixing with Beaufort Sea water) is . rather large when applied to the estimated
115 x 106 metric tons of sediment brought to the sea by the Mackenzie
and Peel Rivers . Using a ca'tion exchange capacity of 15 meq/100 g dry
sediment, the annual exchange capacity of sediments supplied to the Mackenzie
Delta is roughly 17 x 10 12 meq yr-1 . Most heavy metals and some synthetic
organic materials resulting„from technological activities in the Mackenzie
Valley will-likely-be
transported to the Delta by sorption or on exchangeable
sites of suspended sediments (Gibbs, 1973 ; Menzel, 1974 ; Gardiner, 1974 ;
Reddy and Perkins, 1974 ; McHenry et at ., 1974) .
a
The lake sediment samples from' the Mackenzie Delta (Table 5) have much
higher exchange capacities (7-47 meq/100 g) and are likely to be greatly
influenced by changes in ionic composition of the overlying lake waters
(i .e . freezeout of dissolved salts, or contamination from technological
operations) . These sediments would probably act as a sink for added heavy
metals, which would greatly increase the retention time of these metals in
lakes that are infrequently flooded .
Lake-Controlled
Rivers
Rivers with large or many lakes in their watersheds usually do not fit
the relationships shown in Figs . 1-6 . This is because the lakes act as
reservoirs for sediment collected by tributaries to the lake, and the lake
outflow carries little or none of the sediment eroded from the watershed
of the lake . For this reason, lake-fed rivers are usually relatively free
of suspended sediments and have a more regular seasonal distribution of
discharge (i.e . such as Group 3 rivers and Mackenzie River at Norman Wells
in Table 1) . An exception to this is the Brackett River which has been
ratherr turbid in 1972-74, yet drains a lake-rich watershed (see Campbell,
1975 for Brackett River data) . In general, this group of rivers probably
carries much less sediment than their maximum capacity based upon discharge