Investigation of major and trace element distribution patterns and pollution status of the surficial sediments of a microtidal inner shelf influenced by a transboundary river. The case of the Alexandroupolis Gulf (northeastern Aegean Sea, Greece)

摘要

The present investigation examines the distribution patterns of major and trace elements of surficial sediments of the Alexandroupolis Gulf (NE Aegean shelf) which are influenced by the influxes of the transboundary river Evros. Fifty-three surficial sediment samples were analysed for 25 major and trace elements, together with the CaCO3, TOC and mud content. Factor analysis was conducted in order to reveal the major processes that control their behaviour. Pollution indices (enrichment factor, modified contamination degree) were used to evaluate pollution levels, the most widely used SQGs criteria (i.e. ERL/ERM and TEL/PEL) were used for the association with adverse effects on aquatic organisms whilst a new Index (OEI) was introduced to examine the Overall Environment status. The overall mineralogical and chemical elemental status of the Alexandroupolis Gulf is mainly dominated by the riverine inputs of Evros system, whereas, localised point sources contribute to the pollution status of the study area. According to the pollution indices used element enrichment and associated potential pollution were found to be related mostly to mud-sized sediments (10-30 m depth), whilst increased element concentrations are observed, spatially, close to Evros river mouths, within the harbour, and along the NW coast of the study area. The application of the SQGs on Cr, Cu, Ni, Pb and Zn showed that almost half of the sampling sites may occasionally be associated with toxic effects. However, according to the OEI, only Zn and Pb provide a widespread positive overall enrichment in the study area.