Dissolved organic carbon and nitrate flows in two micro-watersheds with different land uses

Abstract

he impacts of human activities on watersheds can change the quality and possible uses of water resources. In this context, we evaluated the flows of dissolved organic carbon (DOC) and nitrate (NO3) in the surface waters of two micro-watersheds with different anthropic impacts. Water samples were collected from two micro-watersheds with different land uses (regenerated savanna and an agricultural site) from January 2014 to April 2015. In the rainy season, the samples were collected every 15 days, while in the dry season, samples were collected every 30 days. An automatic sampler in the stream collected the composed samples. Water flow was monitored with a sensor that measured the hydraulic load on the sill of the triangular spillway installed in each micro-watershed. The DOC and NO3 contents were analyze via UV-Vis spectrophotometry. The flow was estimated based on the DOC and NO3 flows and concentrations. The DOC concentrations were higher in the Cerrado micro-watershed; however, there was no difference in NO3 concentrations. In both watersheds, there was a significant increase in the concentrations of DOC and NO3 on rainy days, with was more pronounced in the agricultural watershed. The DOC and NO3 flows were higher in the micro-watershed with Cerrado vegetation on days with rain; while on days without rain, there was no difference.