Ecology of the várzea, floodplain of Amazonian whitewater rivers

Abstract

According to the classification of Sioli (1950, 1965a, 1968b), Amazonian rivers rich in suspended solids are called whitewater rivers. In addition to the high sediment load they differ from other Amazonian water types (blackwater and clearwater) with respect to the chemical composition of the water. The pH value is relatively high (pH 6--7), as is the total amount of dissolved inorganic substances. Electrical conductivity varies between 50 $μ$S ·cm−1 in the lower Amazon, the principal representative of whitewater rivers, and more than 300 $μ$S ·cm−1 in its upper course (Gibbs 1967). According to Furch (1976), Furch & Klinge (1978) and Furch et al. (1982), whitewaters are carbonate waters, characterized by a high percentage of alkali-earth metals compared to alkali metals. This is a common feature of most fresh waters on earth.