ASSESSMENT OF THE IMPACT OF IRRIGATED AGRICULTURE ON WATER QUALITY IN A SECTION OF THE ITAPARICA RESERVOIR, SUB-MIDDLE SÃO FRANCISCO

Abstract

The anthropogenic impacts caused to water resources in an uncontrolled manner, especially through the use of agrochemicals in irrigated agriculture, bring many environmental, economic, social and public health losses. Therefore, it is essential to monitor aquatic ecosystems and control dumping in these environments, in order to guarantee their sustainable use. The assessment of water quality associated with ecotoxicological tests is essential for monitoring the impacts of economic activities installed in water bodies or their banks. To this end, ecotoxicological analyzes were carried out, using the microalgae Desmodesmus armatus as a test organism, physical-chemical and biological, at two sampling points in the Itaparica reservoir (ITAP EF 01 and ITAP 02), in the sub-medium São Francisco and with the herbicide glyphosate, widely used in Brazil and the semi-arid northeast. The sampling points are close to the region of influence of large public irrigated perimeters, between the municipalities of Petrolândia and Floresta, Pernambuco. Tests with exposure of the microalgae D. armatus to water samples from the reservoir did not show a toxic effect. Analyzes carried out with glyphosate showed that at concentrations of 22.082 mg.L^-1, 11.583 mg.L^-1 and 5.937 mg.L^-1 chronic toxicity was observed in D. armatus, after 96 hours of exposure. The water quality of the reservoir is considered satisfactory during the study period, remaining within the standards recommended by current legislation. Already, the analysis of biological bioindicators showed little occurrence of planktonic species, presenting low densities, but with a warning of the need to maintain biological monitoring, since the presence of bioindicator species of eutrophicated waters (phytoplankton and zooplankton) was recorded, in addition the occurrence of Cyanobacteria potentially producing cyanotoxins.