Chemical characterization of suspended sediment of the River Rhine

Abstract

The Rhine River and its tributaries are one of the largest drainage systems in Europe, transporting sediment particles derived from both human and natural sources. The present study aims at characterizing the chemical composition of suspended sediments in the river Rhine and to identify the provenance of geogenic sediments arriving at the Lobith measurement station in the Netherlands near the border with Germany. The analysis was made from samples collected in 9 measurement stations along the main river (2 in the Netherlands and 7 in Germany) obtained from the Rijkswaterstaat (Dutch Ministry of Infrastructure and Water Management) and from the International Commission for the Protection of the Rhine (ICPR). Also we used the FOREGS database (Forum of European Geological Surveys) with measurements in 24 locations in tributary streams in the Rhine catchment. Time series of elements composition, correlation matrixes, and maps of chemical concentrations were for geochemical characterization. Additionally using the rating curve method we estimated the chemical composition to assess the influence of discharge in elements composition. Principal component analysis PCA was carried out in elements positively related with discharge, which were associated to a geogenic source. Chemical evolution of the River Rhine along its measurement station reflect a general decreasing trend in Cd, Pb, Cr, Hg, Cu, P, and Zr in most of the 9 stations in both Germany and The Netherlands. The other elements show similar average concentrations over the entire time range. Among elements with a positive relation with discharge (Q) are aluminum, iron and REE except lanthanum and can be associated to sources with a relative high concentration of these elements like silicates or clay minerals. Principal component 1 (PC1) shows a seasonal pattern that may be associated with the provenance of sediments since in summer the sediment loads are a result of a major contribution of sediments in waters coming from the snow melting of the Swiss Alps, whereas in winter the low temperatures and high precipitations derive in a greater input of sediments coming from low areas. PC2 may be indicating the variation in the formation of organic-clay complexes because of the association between organic carbon and elements related with clay minerals like, K, Rb, Li and Al observed in the dataset. Finally PC3 possibly represents the dilution of organic matter by primary production in particular places in the Rhine catchment and the provenance of sediments of particular locations like the catchments of the rivers Main, Neckar, the French side of the Mosel and the Vosges Mountains.