Use of the land and the soil evolution in the basin of Água Fria I and II drinking water reservoir in Barra do Choça/BA

Abstract

The basin of captation of Água Fria II drinking water reservoir is of strategic importance for the regional development, for it supplies approximately 300,000 people in a region in which hydrous reserves are scarce, including the city of Vitória da Conquista, Ba. The present study aims at characterizing the evolution of the land use in the years of 1974 and 2004, analyzing the morphologic, physical and chemical modifications of the soil under different managements. For the mapping, aerial photographs and satellite images have been used by means of Map Viewer 6.0 software. For the samplings, six glebes have been selected, involving the uses of coffee plantation, pasture and native forest. In the analyzed period, there had been an expansion of the coffee plantation areas (228%), diverse cultivations (45%) and pasture; and a reduction of the wooded native area (-74%) and secondary vegetation (-81%). In 2004, one could find that only 15.7% of the areas indicated for permanent preservation were occupied by native forest. As a result, the soil became acid and poor, with low Cationic Exchange Capacity, high amounts of Al3+ and H+, and very low levels of P, Ca2+, Mg2+, K+ and Na+, reflecting the poverty of the origin material (Detritus Coverings of the Tertiary-Quaternary), with dominant sort of dystrophic Yellow Oxisol. The coffee plantation under conventional system was the type of management that affected most the characteristics of the soil such as distribution, size and stability of aggregates, as well as loss of organic matter and increase of Soil Density. As a consequence, damage for the fertility and the storage of the water in the hydrographic basin was observed.