Delimitação automática das áreas de preservação permanente e identificação dos conflitos de uso da terra na bacia hidrográfica do rio Sepotuba - MT

Abstract

The Brazilian Forest Law # 4,771/65 and the CONAMA Act # 303/02 instituted permanent preservation area (PPAs) norms. PPAs have a vital role within a watershed, being responsible for ecosystems maintenance, preservation and conservation. The watershed as system is composed of social, economic, demographic and biophysical sub-systems interrelations. The study objectives were: to map the deforestation in the Sepotuba River watershed, in Mato Grosso State, Brazil, occurring from 1984 to 2004, with fiveyear intervals, using thematic images obtained from the TM/LANDSAT sensor; b) to delineate automatically the watershed permanent preservation areas and to identify the land use conflicts occurring from 1984 to 2004; and c) to evaluate the soils maps, updating their legends in agreement with EMBRAPA classification (1999) and agricultural aptitude for the Sepotuba River watershed, superimposing them over permanent preservation areas, as established by CONAMA CT # 303/02. The land use maps covering the study area were generated from the digital TM/LANDSAT images, obtained in August 1984, July 1989, June 1994, August 1999 and August 2004. Five classes of land use were generated: natural forest, savanna woodlands, sparse woodlands, agro-pastoral lands and water. Results show that the Sepotuba River watershed total area is 984,450 ha. During the analyzed period, natural forest area diminished by woodlands (119%) and agro-pastoril (16.83%) classes. Considering the 984,450 ha basin total area, 296.809 ha (30.15%) were identified and mapped as permanent preservation areas. The PPA categories defined for the basin were: riparian forest with 55,166 ha, spring-waters and their contribution areas with 96,100.56 ha, upper third of basin with 146,369 ha, upper third of hilltops with 20,616 ha and steep slopes greater than 45o with 0.36 ha. The total occupied land use areas within the Sepotuba River watershed PPA categories was 86,161 ha (29.03%). The largest soil classes in the watershed were: PVAd1 257,669 ha (26.17%), PVAd3 107,678 ha (10.93%), RQod1 155,512 ha (15.8%) and RQod2 248,033 ha (25.19%). The 4p agricultural aptitude subgroup occupied the largest area, with 544,904 ha (55.35%) of total basin area, followed by the subgroup 4(p) with area of 248,033 ha (25.19%). Only 176,771 ha (18%) of the watershed area were considered suitable for diverse agricultural activities. It is concluded that the use of geographical information systems and satellite images are important tools for generating excellent data bases. The methodology for automatic delineation of permanent preservation areas facilitated land use map generation, proving suitable for use in the implementation of adequate watershed management. Additionally, these maps can facilitate permanent preservation area delineation in the field, as well as be used in government surveillance to identify and locate the areas of land use conflict, making possible, in an unprecedented way, application of the Forest Law.