Avaliação de processos erosivos na base de operações geólogo Pedro de Moura - Coari, Am

Abstract

In Geologist Pedro Moura Operational Base (BOGPM – portuguese acronym) in the city of Coari, Amazon – Brazil forest gaps are opened and the top layer of soil are removed in areas originally covered by primary forest for installation of exploratory wells of oil and gas, civil engineering and road constructions. Those processes exposes soil subsurface layers on the surface that suffers then the direct action of rainfall, wind and sunlight. These activities accelerate the degradation process by changes in soil physical and chemical properties and improve the erosion processes. Studies of impacts on the soil of this oil exploration in areas of primary forest in the Amazon is unprecedented. This study aimed to quantify the losses caused by soil and water erosion in a standard plot for studies of erosion with bare soil (D), soil covered by litter (L) and soil under primary forest (F). To determine the factors of Universal Soil Loss Equation (USLE) and assess and compare to the standart method the losses of soil by the method of changing the soil surface estimated by soil depletion using metal pins. The experiments were conducted in a micro watershed representative of average conditions of soil and slope of the BOGPM to quantify the erosion of the region. The quantification of soil and water losses were carried out in two experiments to collecting water and sediment. The plot had 4 x 22 m aand were located in a clearing sloped area. A plot of 3 x 11 m was located in an area of primary forest. To calculate the erosivity of rainfall data from July 2009 to June 2010 were used. They were obtained by automated rain gauge connected to a data collection system. We collected soil samples disturbed and undisturbed from depths of 0-10 cm for physical and chemical analysis. Estimates of soil losses showed a range from 0.06 to 5909.52 t ha-1 yr-1. The erosivity in BOGPM was estimated to be 9344.59 MJ mm ha-1 yr-1. Erodibility values determined for treatments D, L and F were 0.902, 0.011 and 0.003 t ha-1 MJ-1 mm respectively. Indices for vegetation cover and conservation practices for soil covered with litter and soil under primary forest were 0.0040 and 0.0017 respectively. The soil loss determined by the pin method was 190 t ha-1year-1 which values is much lower than the standard method. The values of soil losses estimated by USLE for the bare soil are among the largest ever recorded in Brazil, which is above the soil losses accepted by the FAO. However, the simple practice of covering the soil with litter lowers the soil losses at acceptable levels, reducing losses by up to 99.95%. It clear indicate the importance of keeping the soil covered and the potential use of the litter for controlling water erosion.