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

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The total mass of sediments removed yearly from the watershed of
each river, is given in Table 3 . The rivers of Group 1, with large watershed
areas and annual discharges, carried vast amounts of sediments compared to
the smaller rivers and streams of Group 2 . In order to compare natural erosion
.rates of sediment from large and small watersheds, the annual mass of sediment
transported was divided by the watershed area of the river . This
resulted in an estimate of the average annual mass of sediment carried
away from a square kilometer of the land drainage area of a river . This
treatment of the data (Table 3) indicates that the watersheds of small
streams yielded much less sediment to the stream-per unit watershed area
than did the large watersheds in Group 1 .
The annual mass of sediment transported per unit watershed area was
positively related to annual discharge (Fig . 2) . Rivers with annual discharges
greater-than about 5 km3yr-1 transported 36 to 126-metric tons of
suspended sediment per km2 of watershed area, while rivers and streams with
discharges from 0 .01 to 2 km3yr-1 transported 0 .2'to 12 metric tons of
sediments km-2yr-l . Some idea of the seasonal variation in these parameters
can be obtained from Fig . 2, where,-,3 years of discharge and sediment transport
are given for the Willowlake River, Liard River at Ft . Liard, and South
Nahanni River above Virginia Falls : . .
Bedload
We tried to estimate the annual movement of cobbles and small boulders
in the bed- of Jean Marie River (50'km SE of Ft . Simpson) . Jean Marie
River has a watershed area (2,960 km-2) a little larger than Martin River,
and is probably similar to Martin River in its annual discharge pattern,
although it carries very low concentrations of suspended sediments (see
Campbell •et aZ ., 1975) . We recovered over 90% of the painted stones that
were placed in . the stream bed, and found that the maximum distance moved
in a year was less than 2 meters . Small stones (0 .10 kg) moved the most,
while larger boulders (10-27 kg) moved very little (maximum of 0 .2 m for
10 kg stones) or not at all .
Oxygen Demand of Sediments in Water
Sediments from the banks of, the Harris River do consume measurable
.amounts of 02 from water at 20-220C in the dark (Table 4) . These data
indicate that 02 consumption per unit time was not related to the mass of
sediment added, nor to the fraction of organic matter in the added sediments
. However, Table 4 does indicate that sediments added to oxygenated
water may cause a reduction in 02' concentrations over a period of 10-30
days .
Similar experiments were .done in situ on Harris River on 1 August
1974 . In this small, clear water stream, sealed, clear glass bottles
(with varying amounts of suspended sediments added) were suspended in the