Efeito do uso do solo na qualidade da água de reservatórios do semiárido brasileiro

Abstract

A substitution of native vegetation for anthropogenic activities in a drainage basin, the result is not a nutrient course for aquatic ecosystems, reducing the water quality of these environments. The semi-arid region of the Brazilian Northeast is not available for the creation and creation of human resources, it is even more susceptible to erosion, which can exacerbate the problem. To identify as variables that can compromise the water quality of sources and of sum of importance for a management of the basins, aiming to generate public policies of protection to the water sources. This work aims to verify how the relationship between the soil use of the drainage basin and water quality variables of 7 reservoirs inserted in the Piranhas-Açu and Apodi-Mossoró river basins without Brazilian semiarid (Rio Grande do Norte - RN). A delimitation of drainage basins, as well as soil occupation applications, is performed using geoprocessing tools such as Taudem and the SCP plugin applied without Quantum Gis software, classifying uses in: dense vegetation, sparse vegetation, exposed soil, urban agriculture and water. The water quality data were obtained together with a state program of monitoring of surface waters and selected variables were total phosphorus, total nitrogen, thermotolerant coliforms, total solids, cyanobacteria and chlorophyll a density. Seven drainage basins were analyzed and Pearson correlation analyzes were performed between reservoir water quality and soil use for the year 2009. Significant negative correlations were found between dense vegetation and total phosphorus (r = -0.96; P = 0.01), and with cyanobacterial density of the reservoirs (r = -0.83 and p = 0.04). Another result to be highlighted was a positive correlation (r = 0.82; p = 0.04) between cyanobacteria density and an agricultural activity in the drainage basin. On the other hand, these results show that the reduction of the native vegetation percentage and the increase in agricultural activity tend to worsen the water quality by increasing the eutrophication process with the occurrence of cyanobacteria blooms.