Hydrosedimentological dynamics in the Guarani aquifer system, Ribeirão Preto, State of São Paulo, Brazil

Abstract

This research evaluated the effects of agriculture on hydrosedimentological dynamics in the city of Ribeirão Preto in the State of São Paulo, Brazil. Physical and chemical analyses of the soils of the Ribeirão Preto hydrographic sub-basin were carried out. A water erosion susceptibility map was generated using the Revised Universal Soil Loss Universal Equation as well as water level and potentiometric depth maps of the studied region. Using geophysical data, a local three-dimensional geological model was prepared that clearly differentiates the outcrop regions of the Guarani Aquifer System. The research results indicate that the key reasons for hydrosedimentological changes under intensified erosion processes are conventional management and forest fragmentation, which cause soil losses above the region’s average tolerance limit of 8.5 Mg ha-1 year-1. Apart from soil damage, the calculated soil loss of about 1 million tons per year leads to a high risk of contamination in the Guarani Aquifer System. In regions located north of Ribeirão Preto, where the Guarani Aquifer System is shallowest, the risk of contaminants diffusing through agriculture is very high. In this context, modelling hydrosedimentological dynamics is of great importance as it enables accurate evaluation of the natural susceptibility of the aquifer to diffuse contamination. It also helps to identify sites that exceed the tolerance limit for soil loss, which are critical for conservation. However, there are no safe levels of soil loss, and attention should be paid to all areas that have soil loss values above what is considered natural. Soil losses for areas in forests were calculated as 0.03 Mg ha-1 year-1, which is well below the average for land under agricultural use (2.03 Mg ha-1 year-1). The results of this research reveal critical hydrosedimentological dynamics in the studied area that affect both the quantity and quality of the water of the Guarani Aquifer System..