Assessment of Soil Erodibility of Different Land-Use Types in a Small Mountain Watershed

Soil erosion is a major degradation process for Bulgaria, which is particularly widely spread in its south-western part (the Struma and the Mesta rivers basins), the southern slopes of Stara planina and the east Rhodopy mountains. The objective of this study was to assess the soil erodibility in case of different types of land use - abandoned arable lands (pasture lands, a sampling site, maintained as a fallow land) and oak branch wood management forests of the Sedelska river basin, a tributary of the Struma river. The Wishmeier et al. (1971) nomograph and the Grade Assessment Method (GAM) used in MERA projects (MARS and Environmental Related Applications) have been applied for the erodibility index calculation. The ArcGIS 9.2 software was used in order to present the spatial distribution of the input data. By integrating digital image processing and a geographic analysis of soil databases, rapid assessment of the relevant soil characteristics was done. The calculated values through the nomograph for soil erodibility vary from 0.028 to 0.044 (Mg/ha)[(M.Vha)(mm/h)](-1). The data obtained show that the values of the erodibility coefficient for soils on the slopes with sunny aspects are higher in comparison with that on the shady ones. According to the classification adopted in the frame of the grade method for erodibility assessment, weak, moderate and high degrees have been established for soils from the studied watersheds. No differences were observed for the erodibility degrees for the soils on the slopes with different aspects and a land-use type when the grade method for erodibility assessment was applied.