Physicochemical Conditions in the Floodplains

Abstract

The different water colors of Amazonian rivers are documented in the river names e.g., Rio Negro (black river), Rio Branco (white river), Rio Claro (clear river), Rio Verde (green river), and indicate differences in water quality. Sioli (1950) related water color to specific conditions in the catchment areas and recognized three main water types based on water color, load of suspended solids, pH, and load of dissolved minerals, indicated by the specific conductance.-White-water rivers have a muddy color derived from the high sediment concentration. They are relatively rich in dissolved minerals and have a near-neutral pH value. Sediments and dissolved minerals are derived from erosion in the Andes and the Andean foothills. Water and flood-plain soils are relatively fertile.-Black-water rivers have dark transparent water due to high amounts of dissolved humic substances. These substances are formed mainly in podzolic soils which occur in small patches throughout the Amazon basin, but are concentrated in the catchment area of the Negro River (Klinge 1967). The water is acidic and the amounts of dissolved inorganic substances are low. Water and floodplain soils are of low fertility.-Clear-water rivers drain areas where there is little erosion. Their water is transparent and may be greenish. The pH varies from acidic to neutral depending upon the geology of the catchment area. The amounts of dissolved minerals are small to intermediate. The fertility of the waters and floodplain soils is variable, but it is lower than that of white-water rivers.