Improvement of a Major Naturally-Occurring Amazonian Lowland Wetlands Classification by means of the Classical Knowledge of River Water Hydrochemistry: Major Cations E. A. Ríos-Villamizar*, M. T. F. Piedade*, F. Wittmann**, T. M. Carvalho* and W. J. Junk*** * Instituto Nacional de Pesquisas da Amazônia (INPA), Av. André Araújo, 2936, Aleixo. CEP 69060- 001. Caixa Postal 478, Manaus, Brazil. (E-mail: eduardorios17@hotmail.com) ** Max Planck Institute for Chemistry, Biogeochemistry Department, Mainz, Germany (E-mail: f-wittmann@web.de) *** Universidade do Estado do Amazonas (UEA), Manaus, Brazil. (E-mail: wjj@evolbio.mpg.de) Abstract Water and soil chemistry provide important parameters for biogeochemical cycles and determine management options in wetlands. The first scientific classification of Amazonian water bodies was elaborated in the 1950s by Sioli. He used water color, as well as physical and chemical parameters, to explain limnological characteristics of the large Amazonian rivers and to relate 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 hydrochemical variability of Amazonian rivers and wetlands. The distribution of alkali and alkaline-earth metals allows to distinguish well among the three classical water types and to categorize other water bodies. Refined results, including additional water chemistry variables and data from other rivers and streams throughout the Amazon basin, are being developed in order to subsidize the wetlands classification system. Keywords Amazon basin, Water quality, Water types, Major Cations INTRODUCTION Classification of water types with the use of hydrochemical quality Chemical composition of water and sediments ranks third in importance for wetlands classification because of its fundamental importance for life in water and wetlands. Chemical content influences not only the occurrence of organisms but also primary and secondary production in wetlands. Water and soil chemistry provide important parameters for biogeochemical cycles and determine management options. Pre-Columbian populations categorized rivers by the color of their water. This criterion was adopted by European immigrants and is evident today in names like Rio Claro, Rio Preto, Rio Negro, Rio Branco, and Rio Verde (Clear River, Black River, Black River, White River, and Green River, respectively). Native and colonial inhabitants of the Amazon knew that water color was related to specific ecological properties such as fish richness, soil fertility, or mosquito abundance (Junk et al., 2011). The first scientific classification of Amazonian water bodies was elaborated in the 1950s by Sioli (1956). He used water color, as well as physical and chemical parameters, to explain limnological characteristics of the large Amazonian rivers and to relate these characteristics to the geological and geomorphological properties of their catchments (Figure 1).