TOTAL MINERAL DISSOLVED TRANSPORT BY WORLD MAJOR RIVERS / Transport en sels dissous des plus grands fleuves mondiaux

Abstract

World variations of dissolved transport Td [t km⁻² year⁻¹] and major ion content S [mg 1.⁻¹] with runoff q [1. s⁻¹ km⁻²] and solid transport Ts [t km⁻² year⁻¹] are examined on the basis of 40 of the world's biggest rivers (basin area A >400 00 km² or discharge Q > 5 000 m³ s⁻¹). For each river estimates of A, Q, S, Td and Ts are given and two subsamples are considered according to the size of the rivers. For each subsample it is found that S is inversely related to q, Td is directly related to q and to Ts. The ratio Ts/Td is highly variable but generally increases when Ts increases. Climate dominates S variation and relief Td variation; wide scatterings of S and Td are due to the other factor. On a world scale relief is the main factor controlling variations of Td with Ts. The direct relationship between Td and Ts confirms the work of Alekin and Brazhnikova in the Soviet Union, while the inverse relationship found by Judson and Ritter in the conterminous USA seems to be a minor trend due to the influence of climate surpassing relief. The total sample of rivers considered covers 48 per cent of the continental area draining to the ocean and represents 44 per cent of the world's runoff. If this sample is taken as representative, dissolved transport of material appears to be dominant or equal to solid transport for about 35 per cent of the world's continental surface. A typology of dissolved transport by major rivers is given according to their morphoclimatic features. If chemical transport is a major process on the earth's surface, the solid material carried by the rivers to the ocean as a whole is five times more than the dissolved transport: 20 × 10⁹ t year⁻¹ according to Holeman as compared to 3.25 × 10⁹ t year⁻¹ on the basis of these 40 rivers.