This work was carried out in the northeastern region of Pará State with the purpose of studying the factors that control the chemism of both spring and well waters. They are waters of aquifers constituted of alteration products of granites (Tracuateua), metassediments(Santa Luzia), metavolcano-sediments(serra do Piriá) and apatite-hornblendite (ilha de Itacupim). Waters in contact with limestones were also studied. Most of these waters purposes. The are used with local population supply waters were collected in restricted zones covered by Amazonian rainforest, in areas that support second growth vegetation(capoeira) and in jungle clearings. The collect period was 1992 dry season, 1993 dry and rainy seasons, 1994 rainy season and in 1995 dry and rainy season. Petrographic and mineralogical study of alteration products and in some cases of the bedrock, indicate the possible influente of these materials in the water composition. The pedogenetics processes taking place in the studied zones were characterized. The potential of these zones for occupation purposes were also evaluated. In Tracuateua, Santa Luzia and also in the Serra do Piriá saprolitic tone, the aquifers are formed by highly weathered products, constituted basically by quartz, kaolinite and iron oxi-hidroxides. In the metavolcano-sediments/lithomarge or apatite-hornblendite/lithomarge interface, minerals like biotite, albite or apatite are frequents. The upper layer (20 cm deep) of the soils in these areas is poor in bases and displays a pH value of about 5,0. The alteration products of calcareous are base saturated, presenting pH about 8,0 and are constituted of quartz and kaolinite, with calcite in small proportion. The content of organic material in soils, about 12% in preserved areas and less than 3% in degraded areas, reflects the nature of the vegetal coverage. Waters in contact with the most weathered products are chloride and sodium rich, acidic (average pH 4,4), poor in solutes(TDS < 30 ppm), mainly of pluvial origin. Waters in contact with less altered products, derived from metavolcano-sediments and apatite-hornblendite, raise the base, silica or phosphate content, which are derived principally from the hydrolysis of primary minerals. In waters from calcareous areas the relation HCO3:Ca+Mg1 indicates carbonates dissolution. They are calcium and bicarbonate rich, righ in solutes(average TDS 230 ppm), and presents pH value about 7,0. When in contact with clay layers that contains pyrite, waters becomes sodium and sulphate rich and acidic (pH 5,0). Marines aerosols, vegetal detritus and domestic waste waters are localized sources of solutes, while the organic acids, together with the scarcity of bases, are responsible for water acidity. The upper layer of the soils of the degraded areas shows intense eluviation with subsequent relative enrichment in quartz. The use of these lands for agricultural purposes requires nutrient reposition. Where sandy-clay sediments cover limestones, the pH value is about 5, what enables the plants to take more efficiently the marine nutrients which abound in the calcareous sediments.
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