River transport

Rivers transport suspended sediments derived from the disintegration of basin surface layers. With reduced velocity, sediment is deposited in the river channel. The finest material is carried to the sea. It has been estimated that the average mechanical denudation rate for continents is 0.056 mm year (35). This is based on a total suspended load of 13.5 x 10 metric tons year (S). Presently, about two-thirds of the world s total suspended sediment load derives from Southern Asia and large Pacific Islands. Berner has estimated the increase in sediment loss in the U.S. and world since prehuman times to be approximately 200% (35). Current estimated erosion rate from the major land forms is provided in Table I. The relatively recent construction of large sediment trapping dams that normally caused sediment to be deposited in river valleys or transported to the ocean has drastically reduced sediment yields in great rivers. 

In addition to runoff, rivers transport products of upland weathering to the oceans, forming a key link in the tectonic cycle of uplift and erosion. This interaction will be explored further in Section 6.6. 

River transport of organic carbon, estimated earlier as 0.1 Pg C/yr, brings the sum of non-respiratory outputs to 7 Pg C/yr. Total respiration should therefore be around 50 Pg C/yr. This figure is in agreement with estimates of soil respiration rates determined from compilations of ecosystem types and their measured soil respiration rates (Ajtay et ai, 1979). 

Chabaux F, Riotte J, Dequincey O (2003) U-Th-Ra fractionation during weathering and river transport. Rev Mineral Geochem 52 533-576... 

Rivers transport clay minerals primarily as part of their suspended load (silts and clays). The silt-size fraction is composed of quartz, feldspars, carbonates, and polycrystalline rocks. The clay-sized fraction is dominated by the clay minerals illite, kaolinite, chlorite, and montmorillonite. In addition to suspended particles, rivers carry as a bed load larger size fractions. The bed load constitutes only 10% of the total river load of particles and is predominantly quartz and feldspar sands. 

River transport of clay minerals into the ocean is spatially and temporally variable. The global annual suspended load of river sediment into coastal waters currently averages 12.6 X 10 ton. This flux is approximately 10% less than was delivered before humans began damming rivers. (One notable exception is the Mississippi River, whose sediment load has increased due to very high rates of soil erosion. The riverine sediments deposited in the mouth of the Mississippi River form one of the world s largest deltas.)... 

The major source of solutes and solids to the ocean is via river transport. The only major ion with a direct source associated with hydrothermal input seems to be calcium. The hydrothermal input of DSi is also significant. Volcanic gases are presently contributing a minor amount of HCl and sulfur gases (H2S and SO2). Each of these sources is discussed next with primary focus on how terrestrial chemical weathering provides most of the major ion input the oceans. 

Analytical chemistry is interested in information that can be obtained from material objects or systems. In more down to the earth terms this means that analytical chemists try to tell something new about objects, goods, bulk material or material systems. The way they obtain this information changes with the problem. In most cases they try to get the information from the qualitative or quantitative composition. A vast array of instruments and methods is to their disposition but most of them have one thing in common their size is limited and the way they obtain information is destructive. That means that as a rule the analytical chemist cannot or will not use the whole object in his analysis machine, but that he uses only a small part of the object. In practice this fraction can be very small the amount of material introduced in the analytical method rarely exceeds 1 g, but as a rule is not more than 0.01 to 0.1 g. This can be part of a shipload of ore, say 10 g, or a river, transporting 10 -10 g water/day. In many instances this fraction is larger, but a fraction of the object to be analyzed of 10 -10 is common practice. 

Several global and continental-scale studies of total organic carbon (TOC) export in large rivers have focused on the question of whether the oceans are an important sink for atmospheric C via river transport of... 

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