Geochemical baseline of trace and major elements in sediments in the Rio de Ondas Basin (Bahia, Brazil)

Abstract

Sediments provide essential information about geochemical processes occurring in aquatic systems and are useful to monitor temporal changes in metals concentrations. In this work, we conducted a geochemical survey in the Rio de Ondas basin, situated in the inland cerrado area from the northeast Brazilian region, to establish environmental reference values to identify metal origins related to anthropogenic and natural sources. Also, we evaluated the temporal dynamics of soil to assess the anthropic pressure over the soil surface and its potential effects on geochemical compositions of sediments. To this end, we combined geochemical and Geographic Information System (GIS) information, including remote sensing imagery, X-ray diffraction analysis, and geochemical analytical tools. We applied multivariate statistical analysis, determination of Geoaccumulation Index (Igeo), and enrichment factors (EF) to interpret the dataset. The results showed that 47.35% of the Brazilian cerrado in this zone was suppressed due to agricultural activity expansion. Mineralogy analysis indicated the presence of quartz silicates, varying from 65.1% (w/w) to 86% (w/w). Overall, the sediments showed low metal contamination levels and moderate levels near urban centers, probably due to domestic sewage discharge. It was also observed in very similar proportions of mineral constituents, obtaining environmental reference data and their associations with the region's geological formation. Thereby, sediment geochemical compositions probably reflect weathering processes, which may accelerate due to landscape modifications induced by economic activities, notably agriculture.