Original paper

Water and sediment loss through runoff in areas of forest and pasture cover in southwestern Amazonia – Acre – Brazil

Santos, Waldemir Lima Dos; Augustin, Cristina Helena Ribeiro Rocha

Abstract

The southwestern area of the Amazon rainforest has undergone rapid transformation through the substitution of forest for pasture cover. In order to identify differences in water and sediment loss through runoff in areas of forest and in areas where the forest has been transformed into pasture, four parcels of 10 m2 were installed, two in each type of cover on two slopes of the Judia drainage basin in the state of Acre, Brazil. The data was collected during the rainy season between 10/2010 and 03/2011. At each plot daily precipitation, vegetation, infiltration capacity, porosity and penetration resistance in the soil were measured. In the pasture cover of both slopes the total precipitation reached 1.172 and 1.145 L/m2 with water losses of 162.94 and 134.73 L/m2 and sediment loss of 32.032 and 25.972 g/m2, respectively. In the forested plots of the slopes, the total rainfall was 936 and 935 L/m2, with water losses of 84.01 and 82.13 L/m2 and sediment loss of 72.372 and 86.090 g/m2, respectively. Test of variance (T-Student) identified significant differences in water loss in the pasture plot compared to that of the forest cover (p = 0.000) on Slope 1. However, sediment loss (p = 0.168) presented higher values for the parcels covered by forest. On Slope 2 there were no significant differences in the values of water loss for the parcels of each type of vegetation cover (p = 0.289). The difference in the value of sediment loss of the forest parcel on Slope 2 (p = 0.0911), at 10% significance level, was significant in comparison to that of grass cover. The higher values of sediment loss through runoff in parcels covered by forest, seems to be associated with a more intense soil disturbance caused by mesofauna coupled with the intensity of precipitation caused by the accumulation of rainwater on the leaves. Alternatively, higher levels of compaction may have favored greater water loss in pasture areas.

Keywords

acre-amazonialand coverexperimental plotssediment lossoverland flow