Áreas de solo exposto intensificam o processo de eutrofização no semiárido brasileiro

Abstract

The replacement of native vegetation by anthropic activities in a watershed usually results in the transport of nutrients to aquatic ecosystems, reducing the water quality of these environments. The semi-arid region of the Brazilian Northeast meets this rule and, because it has young soils, is even more susceptible to erosion, which can exacerbate the problem. Identifying the variables that can compromise the water quality of springs is of utmost importance for the management of the basins, aiming to generate public policies of protection to the water sources. The objective of this study was to evaluate the predictive power of the environmental variables of soil use and occupation on the limnological variables of thirty-three reservoirs inserted in the Piranhas-Açu and Apodi-Mossoró river basins in the Brazilian semi-arid region (Rio Grande do Norte - RN). The delimitation of the sub-basin, as well as the analyzes of land use and occupation were carried out using geoprocessing tools such as Taudem and the SCP plugin applied in the Quantum Gis software, classifying uses in: dense vegetation, sparse vegetation, exposed soil, urban, agriculture and water. The water quality data were obtained from a state program for monitoring surface water and the selected variables were: total phosphorus, total nitrogen, Biochemical Oxygen Demand and chlorophyll a. Statistical analyzes of Pearson correlation and Principal Component Analysis (PCA) were performed between limnological and soil use data for the year 2009. Significant positive correlations (p <0.01) were found between the exposed soil areas with limnological variables total nitrogen and total phosphorus. The PCA made showed that the relationship between the use of the soil and the water quality of the reservoir is more pronounced in the Apodi-Mossoró basin. Therefore, these results show that the reduction of the native vegetation percentage and the increase of the exposed soil areas tend to worsen the water quality by intensifying the eutrophication process, which may lead to cyanobacteria blooms, and according to other studies in this region, these areas are associated with agricultural and extensive livestock activities, and the soil types present in the basins are also fundamental variables in the understanding of the process of enrichment of the water bodies.