Understanding the geochemical composition of alluvial sediments in a complex environmental system – A case study of the Mura/Mur river

The study provides a comprehensive investigation of the geochemical properties of stream and alluvial sediments in an area characterised by a complex natural (geochemical) and anthropogenic environment of the transboundary Mura River (Austria, Slovenia, EU). A total of 65 sediment samples from active river channel and tributaries, and 59 samples from 6 floodplain sediment profiles were collected and analysed. ICP–MS analysis was used to determine the levels of 59 elements in two fractions (<0.063 and 0.063–0.125 mm). Natural (geological) and anthropogenic factors influencing the elemental composition were determined. The sediments showed a low degree of weathering in the upper part of the river and a moderate degree in the middle and lower parts. They are enriched with As, Co, Cr, Cu, Mo, Ni, and Sb compared to the median values for the European stream and floodplain sediments. This can be a consequence of the presence of natural ore mineralisation in Upper Styria along with related lithological features. Factor analysis revealed four natural geochemical associations (K–Ba–Rb–Ga–Li–Tl–Cs–Be–Al–Cu–V; Th–YREE–U; Zr–Hf–Nb; Na–Sr), one anthropogenic association (Cd–In–Zn–Pb) and two combined (geogenic and anthropogenic) associations (Ni–Cr–Mg–Co–V and Fe–Sc–Ti–Nb). Particle analysis by SEM/EDS was used to identify characteristic carriers of specific elements and potentially to determine their sources.