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HYDROCHEMICAL CLASSIFICATION OF AMAZONIAN RIVERS: A SYSTEMATIC REVIEW AND META-ANALYSIS

Water and soil chemistry provide important parameters for the study of river ecology and biogeochemical cycles. Furthermore, they determine management options of rivers and connected wetlands. The first scientific classification of Amazonian water bodies was elaborated in the 1950s by Harald Sioli. He used water color, as well as physical and chemical parameters, to explain limnological characteristics of the large Amazonian rivers and related these characteristics to the geological and geomorphological properties of their catchments. Today, an increasing amount of hydrochemical data indicate that the chemical composition of Amazonian water bodies varies much more than assumed by Sioli. Nevertheless, his simplified classification is useful for describing the natural physical and chemical variability of Amazonian rivers and wetlands. The electrical conductivity, pH-value and the distribution of major cations and anions allow to distinguish well among the three classical water types (white, black and clear) and to categorize other water bodies as intermediate types, in order to subsidize a more detailed classification system of Amazonian fresh waters. This classification indicates in lower order tributaries the existence of many transitional hydrochemical stages and the change in water quality between rainy and dry seasons. These differences have to be considered in the general Brazilian and Amazonian wetland classification systems in order to formulate recommendations for their sustainable management.