Hydrochemistry and Geology in the Brazilian Amazon Region

Abstract

In the Brazilian Amazon Region the relations between chemistry of waters (groundand running waters) and the geology of their catchment areas are qtrite obvious. The archean massifs in the north and south of Amazonia produce chemically very poor and pure waters, with low pH. Still poorer and more acid are the waters in the pliocene-pleistocene "Series of the Barreiras" ancl "Formation Parâ" areas, while in the west, in the zone of the "Formation Pebas", of same geological age, also richer and less acicl waters occur. In all these geological zones, there are spots of bleached sands (podsols), covered with a special vegetation type, which produce "black" waters, while from the yellowish brown-loams (latosols), with high forest cover, clear waters come. The "black" waters contain huge amounts of colouring humus substances while their content in inorganic ions and their pH values are the lowest in all Amazonia. Quite different from the waters in the mentioned geological zones are those in the carboniferous strips, where there are limestone and gypsum layers ancl diabase outcrops, and in the'miocene "Formation Pebas" with also limestone deposits. These waters are generally richer in incirganic ions and have higher pH values. The importance of the chemistry of the Arnazonian waters for an estimation of soil fertility and for human health is mentioned