Land Cover and Soil Loss Multitemporal Analysis: An Application Of Geoindicators In The Pantanal Wetlands (Brazil)

In the Pantanal wetlands (Brazil), one of the largest continental alluvial fan of the world, since the '70s farming and agriculture activities rapidly have been developed, mainly to produce coffee, rice and soybeans. Arable lands and pastures replaced wide areas of native shrubs (cerrado) and forests. As a consequence rapid erosion phenomena in the planalto (highlands) regions and sediment filling of watercourses in the Pantanal developed. The sol id discharge increased, causing accelerated deposition in the channel beds, widening of floodable lands and reduction of productive territories. These facts suggest that geoindicators like land cover and soil erosion changes, must be studied in order to evaluate sustainable development and land management. In this work the land cover changes from 1966 to 1996 were investigated through Remote Sensing and Geographic information Systems (GIS) methodologies. Then, the land cover change effects on soil loss were evaluated through the application of the USLE. Geo-coded land cover data bases were built from aerial photographs and topographic maps (year 1966) and Landsat TM images (years 1985, 1996). Remotely sensed data were classified according to the CORI NE Land Cover legend integrating supervised classification and visual interpretation. The interpretative keys were based on the land cover ground truths collected during field work missions (1997-2000). Moreover soils data were used to improve classification accuracy by means of segmentation techniques. Changes were detected by "post-classification comparison", then multitemporal land cover data bases and statistics were produced. The Digital Elevation Model (DEM) was created by digitising spot heights, contour lines and hydrography from topographic maps at a scale of 1:100,000. The USLE was applied to a pilot area of the planalto region where wide land cover changes occurred alter 1966 (upper Coxim River watershed). Soil, soil erodibility, rainfall erosivity, cropping management and erosion control practice data bases were taken from literature; slope length and steepness factor databases were calculated from the DEM. The results point out that the whole area underwent wide land cover transformations from 1966 to 1985: 35% (about 32,000 km2) of forest and cerrado (savanna) underwent deforestation in favor of agricultural and zoo-technical lands. After 1985, 15% of natural lands were cleared even thought significant re-growth of natural vegetation was detected. Among the physiographic provinces, identified through integrated analysis of DEM, ground slope grid (calculated from the DEM), database of geology and visual interpretation of Landsat TM images, the planaltos experienced the widest land cover changes of the study area (40%, about 23,000 km2). The results from the USLE show that the detected land cover changes induced a meaningful growth of the estimated soil loss from 1966 to 1985 (Delta A about 15 t*ha-1*y-1). These data are in agreement with accelerated erosion phenomena in agricultural and pasture areas observed during fieldwork, and with the increase of solid discharge in the Coxim river known from the literature.