ENVIRONMENTAL REFLECTIONS OF SOIL NUTRIENTS LOSS BY WATER EROSION IN THE PIRAJIBU-MIRIM RIVER WATERSHED (SÃO PAULO STATE)

Abstract

Soils are fundamental for human development and an infinite number of animal and plant species, however, research has shown that their production capacity is threatened because of their impoverishment. For this reason, the study aimed to spatialize the soil nutrients in the Pirajibu-Mirim river watershed, as well as to estimate the loss of these nutrients by water erosion by sub-basin to identify which have a greater contribution of soil particles to the watercourses. The soil was collected in 30 sampling points evenly distributed in the Pirajibu-Mirim watershed at a depth of 0-20 cm and geospatialized in a Geographic Information System (GIS). The Universal Soil Loss Equation (EUPS) was used to estimate soil loss and, afterward, nutrient losses by hydrographic sub-basins were computed. Results showed more significant losses in the Light and Moderate classes, with an average soil loss of 5.92 t/ha.year. The lost soil nutrients showed high values, mainly for calcium (28,525.29 kg/year), iron (15,130.62 kg/year) and organic matter (674,088.91 kg/year). Soil particles can contribute to watercourses and reservoirs compromising the quality and quantity of water through the dam eutrophication and silting, culminating in health and environmental problems.