INFLUENCE OF THE RESOLUTION OF DIGITAL ELEVATION MODEL IN DETERMINING THE TOPOGRAPHIC WETNESS INDEX AND ABILITY TO PREDICT THE SOIL ORGANIC CARBON CONTENT

Doi: 10.12957/geouerj.2015.13452 In this paper Digital Elevation Models (DEM's) were generated using altimetry data from two sources; topographic maps at 1:50.000 scale and altimetry surveys with Real Time Kinematic (RTK) positioning at scale 1:10.000. The objective was investigate the dependence of the scale in determining the Topographic Wetness Index (TWI) for a watershed plateau of Rio Grande do Sul, and evaluate the potential of this index discretize the levels of Total Organic Carbon (TOC) of the soil. The effect of different resolutions on the spatial distribution of TWI was evaluated using descriptive statistics. The analysis of the carbon content and carbon stock in 57 soil sampling points, with the values of the topographic wetness index content was made by linear correlation. The results show that the use of DEMs created with altimetry data from low spatial resolution are inadequate to discretize the area most likely to reach the state of water saturation, mainly due to limitations of positional and vertical accuracy. The use of DEM's created with the best altimetry data, RTK, delimited satisfactorily to areas prone to water saturation. The correlation coefficients between TOC and carbon stock with the values generated by the TWI-RTK data were statistically significant, demonstrating the great potential of this index in the prediction of the carbon in the five layers of soil evaluated and the stock of C to 60 cm for the watershed studied.