Análise da concentração de nutrientes em trecho de rios de duas bacias hidrográficas co diferentes coberturas vegetais na região de Santarém-PA

Abstract

The change of composition of the forest areas and the use of the soil over the Amazon and the mesoregion of Santarém are suffering from accelerated alteration due to the substitution of the traditional and rudimental agriculture techniques to the use of modern equipment and more advanced and automated agriculture. The alteration of the forest coverage causes impacts on the soil, biodiversity and the river basins. The objective of this work is to quantify the concentration of nutrients over the length of the Mojú and Rio Branco rivers considering the use of the soil, as well as the influence of seasonal hydrological changes The system used for geographic information and image classification is the software ArcGis. The quantification of the concentrations of ions was determined by the liquid chromatography method, with the use of a Photometer multiparamether. The evaluation of monthly precipitation was obtained through the operating weather station: BELTERRA - PA (OMM: 82246). The area classification results showed that the Mojú river basin has a total area of 215,466.59 hectares, with 86.51% representing Dense forests, 4.25% of secondary forests, 5.40% of pastures, 2.51 % of agriculture and other non-identified areas. The total area of the Rio Branco river basin is 104.291,29 Hectares with 80.27% of dense forest, 6.93% of secondary forests, 7.82% of pasture areas and 3.23% of agriculture and other non-identified areas. The descriptive analysis of the variation of nutrients indicated that some nutrients have a characteristic variation in certain stretches of rivers and according to the period. Copper reaches peak concentration in the rainy season. The other nutrients showed peaks also in the rainy season in different sections. Iron in rio Branco River, phosphate in the Jatuarana river stretch, the magnesium in the Moju BR 163 river stretch, while potassium showed peaks of highest concentration in Moju Soraya river, Moju BR 163 river, Moju Km 101 extension river and Moju Raimundo river. Nitrate reached peak concentration in the Mojú BR 163 river, the calcium in rio Branco river stretch. However the analysis for the nutrient zinc showed peak concentrations in the less rainy season in parts of the rivers Moju BR 163 and Moju Km 101 extension. For the nutrient zinc, the results indicate that the higher the precipitation the lower the concentration of these nutrients. There is identification of significant differences in nutrient concentrations between the rainy and not rainy seasons, it was identified that this relationship occurred in the stretches of Mojú BR 163 river for copper with the highest concentration in the rainy season and zinc in less rainy season. Mojú BR 163 river for nitrate with the highest concentration over the rainy season.