SURFACE WATER QUALITY AS A FUNCTION OF LAND USE AND OCCUPATION IN TWO SUB-BASINS IN THE SOUTHERN AMAZON

Abstract

Water quality monitoring is essential for understanding and assessing physical, chemical, and microbiological characteristics, while accounting for spatial and temporal variations driven by climate, soil, and land use and land cover. Given this context, the study aimed to evaluate whether surface water quality is affected by land use and land cover in the Renato and Caiabi river basins, located in the southern Amazon region. The Water Quality Index (WQI) and Trophic State Index (TSI) were determined at eight sampling points on the Renato River and five on the Caiabi River across four seasonal transitions (wet, wet-to-dry, dry, and dry-to-wet), following methodologies from Standard Methods for the Examination of Water and Wastewater. The Renato River presented a water quality compliance index exceeding 90%, while the Caiabi River recorded 90.45%, considering Class 2 rivers. For both rivers, parameters such as temperature, acidic pH, low electrical conductivity, turbidity, nitrogen, and chlorophyll a indicated an absence of effluent discharge. Dissolved oxygen, biochemical oxygen demand, total organic carbon, thermotolerant coliforms, and total suspended and dissolved solids exhibited greater seasonal variability but remained within regulatory limits. Both the Renato and Caiabi rivers displayed a "good" WQI and an oligotrophic TSI, indicating low eutrophication potential and an absence of adverse impacts on water usage, despite significant land use and land cover changes within the basins. Keywords: water quality index; LULC; agricultural watersheds; Cerrado-Amazon transition.