Aplicação de geoprocessamento na análise ambiental das bacias hidrográficas do Igarapé Juruti Grande e rio Aruã – Juruti – Pará

Abstract

The study area is located in the region of Juruti, enclosing the river Juruti Grande and Aruã watershed, with 4,560 km2. The region within equatorial humid climate has a mean annual precipitation of 2,223 mm, showing dense forest with great number of vegetal species. The pedology shows essentially yellows latossolos and in the Amazon river flooding plains, hydromorfic soils. This region is placed in Amazon Sedimentary Basin within superior part, a thick package of Cretaceous rocks, poor consolidated, of the Alter do Chão Formation, being recovered by Quaternary aluvial deposits, distinguished that of the Amazon river floodplain. The Juruti Grande and Aruã’s watershed present good conservation condition. However, the Juruti Project for explotation of bauxite is developed in the plateaus of these basins, by Alcoa Inc., passing this area for intense speculation, with great pressure on the environment, being necessary periodic monitoring by competent agencies for maintenance of the balanced ecosystem. Thus, the geoprocessing blunts as an efficient, fast alternative and low cost for this environmental monitoring, evidenced in these research. It were made use of methodologies to manage the natural capital of the inquiry area, developing geographic information systems (GIS), therefore has vital paper in the administration of the space information of the environment, easing the management by digital way of cartographic data and allowing them elaboration of prognostics and diagnostics of environmental problems, underlying the planning and the decision makes. In this way the application of GIS in the inquiry area have great value, once the region of Juruti passes and will pass, for great transformations in ecological and social-economic aspects, letting only more, a marginal region from Amazonia. In the GIS’s building for this area, accomplished the storage of the geometry and the attributes of georreferencing data, radar and satellites images, acquiring in the years of 1972, 1986, 1997, 2000, 2001 and 2005. The multitemporal boarding allowed access information of qualitative and quantitative evolution of the land use and alterations of the natural vegetal covering, making possible, modified analysis of biomas among the different compared years, understood as basic for initial evaluations of the ecology of the landscape, overall with respect to its land covers. The computational procedure made possible an initial evaluation of metric parameters (overall related the paisagistic diversity) of automatic manner, beyond the generation of digital thematic maps. The development and application of these technological methodologies (geoprocessing and remote sensing applied at images of radar and satellites), in the Juruti region, made possible the generation of diverse representative products, as the multitemporal land use maps, declivity correlation with the relief, drainage trends, and others. The thematic and land use classification maps of the area had presented the evolution of landcovers in the four years used as reference. The application of the kappa’s index for the quality of the thematic mapping evaluation pointed a result of 0,72, indicating a very good classification. The thematic maps and the respective comparative graphs had shown that the forest area presented 91.8% of the area in the year of 1986; 87.22% in 1997; 85.57% in 2001 and 74,92% in 2005. The antropics and secondary forests areas, had increased proportionally to the reduction of the area of forests. The correlation map of declivity within relief presented predominance of areas with low declivity, specially the fertile swamp areas and that almost plain reliefs. The regions that had presented ondulate to strong reliefs are mainly, in the central part of the watershed. The interpretation of main neotectonic structures with detailed drainage network analysis considered the straight line trends as drainage trends. It was detected NE-SW directions well narrow characterizing long belts in SE part of the area. Near Amazon river it has NNE-SSW belts.