Material Fluxes on the Surface of the Earth (1994) / Chapter Skim
Currently Skimming:
Origin and Variable Composition of Present Day Riverborne Materials
Origin and Variable Composition of Present Day Riverborne Materials
Pages 61-73
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 61... ...
Dissolved silica originates mainly from the humid tropics, as does total organic carbon derived from soil erosion; ions are relatively more abundant in the temperate regions due to their higher proportions of limestone; TSS originates from mountainous and dry regions found in the temperate zone, and the Huang He river alone accounts for more than 6 percent of the total river load. If the solid transport rate per unit area (Ts)
|
From page 62... ...
Actually, global averages mask the extended chemical diversity of river water and particulates as well as the wide range of river transport rates. The purpose of this chapter is (1)
|
From page 63... ...
a 63 important part of the so-called Black Waters, the less mineralized world waters (Stallard, 1980; Stallard and Edmond, 1981, 1983~. Near the ocean, relatively high ionic contents may result from atmospheric inputs as in pristine streams draining sand deposits in the extended Landes pine forest in southwestern France (Figure 4.1~.
|
From page 64... ...
Concerning TSS, the vegetal cover is one of the four major controlling factors in mechanical erosion, along with bedrock, slopes, and rainfall pattern: unprotected bare soils are sensitive to rainsplash impact, and developed root system lower mass wasting and subsequent erosion. Past geological history in a river basin is seldom considered although post glacial features may affect chemical and physical weathering in many ways.
|
From page 65... ...
Active volcanism, an event DISTRIBUTION OF RIVER WATER QUALITY The distribution of ions, silica, organic carbon, and TSS in world river systems depends on the relative importance of the environmental factors mentioned and on the basin size. Because of the great diversity of environments, particularly of surface rock types, found on the scale of streams and small rivers (area < 1000 km2)
|
From page 66... ...
a set of pristine streams, the Temperate Stream Model, derived from set 1 after systematic correction of atmospheric inputs and selected as representative of the global distribution of rock types (Meybeck, 1987~. The distribution of some ions and silica is given for these small, medium, and large rivers on Figure 4.4 and Table 4.3.
|
From page 67... ...
; Mackenzie, E (n = 100, from Reeder et al., 1972~; monolithologic French Steams, F (n = 250, from Meybeck, 19861; Temperate Stream Model, G (Meybeck, 19871; monolithologic Miscellaneous Streams, H (n = 75, from various sources) ; major world rivers, I (n = 60, from Meybeck, 19791.
|
From page 68... ...
, of total dissolved solids (T`,, sum of major ions and dissolved silica rates) , and of total suspended solids (Ts)
|
From page 69... ...
For specific ele ments, relationships may also be drawn between dissolved and particulate transport. Although this data base is much less documented than total transport rates, the correlation T``i versus Tsi is also positive, except for organic carbon.
|
From page 70... ...
through consideration of the chemical composition of waters from small monolithologic watersheds and of the relative abundance of a dozen rock types at the continental surface. Atmospheric inputs were also reassessed (Meybeck, 1983~.
|
From page 71... ...
For example, the ratio of dissolved silica to total silica transport varies from 0.3 percent for regions of high mechanical erosion to 40 percent for lowlands. CONCLUSIONS The use of present-day river transport data for past geological times, particularly in ocean and climate modeling, should be undertaken cautiously.
|
From page 72... ...
are two essential factors in river transport that can never be well known for the past; and · the great variability of transport rates in today' s rivers suggests that past global inputs to oceans of dissolved and particulate matter may well have varied by one order of magnitude within geologic evolution. · the great variability of transport rates in today's rivers suggests that past global inputs to oceans of dissolved and particulate matter may well have varied by one order of magnitude within geologic evolution.
|
From page 73... ...
(19831. Atmospheric inputs and river transport of dissolved substances, in Symposium on "Dissolved Loads of Rivers," International Association of Hydrological Science Publication 141, 173- 192.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.