MULTIELEMENT CHEMISTRY OF SOME AMAZONIAN WATERS AND SOILS

The rivers flowing through the Amazon Basin are both physically and ch emically heterogeneous. Through detailed geochemical analyses, variabi lity is shown to be primarily controlled by both substrate lithology i n the source region and soil geochemistry in the erosional regime. The solute-rich waters of the Rio Solimoes reflect the drainage from the Andes Mountains and the fertility of the varzea. In contrast, the solu te-deficient waters of the Rio Negro reflect the infertility of the la teritic and podsolitic terrains of the Central Amazon. Rivers flowing through the Precambrian Shield have an intermediate composition. Such observations suggest that it is possible to classify the chemical comp osition of Amazonian rivers according to the soil types in their catch ment regions and vice versa. These findings have profound implications for using water chemistry as an indicator of the agricultural and min eral potential of a region. Results from this study also confirm that precipitation is a significant source of major cations and trace metal s to solute-deficient river systems such as the Rio Negro.