Influence of particle-size on geochemical distribution of stream sediments in the Lese river catchment, southern Italy

This study was carried out in a river catchment in southern Italy to determine some possible relationships between the distribution of chemical elements and size fractions in stream sediments. Through the presence of variations in concentration of some elements in each size fraction, it was possible to examine the influence of particle-size on geochemical distribution of stream sediments. From this point of view, it is very useful to study the Lese river catchment because it is representative of the whole Mediterranean area given its characteristics, which are common to other similar areas. Sediment samples were collected from 13 stations in the catchment area. The chemical compositions of bulk samples coupled with those of some selected particle size fractions were analyzed for 25 elements by using X-ray fluorescence spectrometry and for their sedimentological characteristics. Particle-size analysis was focused on trying to understand how samples from the same site showed different geochemical distribution in the different size fractions. Stream sediments in the study area consist mostly of sand particles. Chemical analyses were performed to determine to what extent the stream sediments retain the geochemical signature of their parent rocks. Some size fractions, and not only the recommended < 150 mu m, allowed testing of the validity of FOREGS procedures, which considers the < 150 mu m to be the optimum fraction for chemical analysis. The elemental values were analyzed according to the various thresholds imposed by Italian legislative Decree No. 152/2006. This study suggests that the geochemistry of stream sediments also needs to be characterized in order to evaluate the potential chemical pollution of an area.