Hydrological and sedimentological impact of the restoration of a degraded area in a semiarid environment

Abstract

The objective of this paper is to assess the effects of both fallow and overgrazing on hydrological and sedimentological responses to natural precipitation. The research has been lead in the desertification area of Iraucuba, Brazil, whose soil is a typical Natric Ortic Planosol, A weak. Sixteen months of experiments have been executed in two hillslopes: a preserved (E_P – 370 m²) and a degraded (E_D – 468 m²). Both hillslopes are very close, having the same climate, soil and topography, differing only on soil use. The precipitation events showed highly irregular space-temporal pattern. The ten-year fallow practice was able to reduce by 2/3 the runoff. The smallest precipitation able to generate runoff was 7.2 mm in E_D and 8.6 mm in E_P. This shows the increase of initial abstraction in the preserved area due to higher interception losses of both vegetation and litter; as well as higher moisture retention in the top layer of the soil. Contrastingly, the highest precipitation unable to generate runoff was identical in both cases (17.0 mm), once the main parameter responsible for this parameter - soil structure – is still similar despite the ten years of fallow. The recession-curve coefficient has strongly been affected by the fallow technique, reducing from 0.107 min^-1 to 0,045 min^-1, indicating the recovery of the base-flow potentiality, which enhances the runoff permanence time. The fallow hillslope yielded 83% less sediment than E_D, leading to better physical, chemical and biological properties of the soil. Therefore, the ten years of fallow were able to measurably enhance both hydrological and sedimentological responses of a degraded semiarid hillslope.