Sub-bacia do rio Gramació/RN: implicações do uso e cobertura da terra sobre os recursos naturais

Abstract

The adoption of the river basin as a management unit is in the appropriation of the system concept, any change, whether natural or anthropic, can affect the constituent elements of the system. Under this bias, the present work has as an empirical clipping the Gramació river sub-basin, comprising 34,32 km2 covering the municipalities of Vila Flor/RN and Canguaretama/RN, both located in the microregion of the southern seaboard of Potiguar, whose main economic activity is the monoculture of sugarcane. The processes resulting from the use and land cover in the sub-basin are justified in the present study the analysis, understanding and discussion of the implications on natural resources, specifically on water quality and forest cover. For this, the methodology of this study involved the empirical approach, following the themes: use and land coverage through the mapping of the 8 subclasses, according to the Land Use Classification System (IBGE), through the aerial and orbital images of the years 2006 and 2011, allowing the temporal analysis of the evolution of the subclass in a quantitative and qualitative way; morphometric analysis of the sub-basin that made it possible to understand the spatial arrangement of the drainage system and; standard of water quality from surface and groundwater sources by means of physical-chemical and microbiological laboratory tests, in compliance with the limits established by current legislation. The theoretical approach brings the concept of river basin and the methodology for its delimitation and legal aspects. Thus, with respect to subclass use and land cover, the results showed losses and area gains among the subclasses, highlighting the temporary crop as the most expressive. Parallel to this, the change in the criteria for the delimitation of Permanent Preservation Areas (APP’s) from the New Forest Code demonstrated a regression in the question of the protection of the surface water body. Regarding water quality, the Gramació River samples showed seasonal and local variations, especially in the dry and rainy periods and at the R-03 and R-04 sampling points, due to the introduction of domestic effluents and by the contribution of sediments from the transport of leached material to the aquatic environment. Regarding groundwater quality, there was no variation in the parameters pH, total coliforms and nitrate, due to the infiltration of the domestic sewage through the black cesspools or septic. The results contributed to the development of a cartography that spatializes the current state of surface and groundwater quality, as well as land use and land cover patterns in the Gramació river sub-basin.