ANTHROPOCENE HUMAN FOOTPRINT IN THE NALÓN ESTUARINE SEDIMENTS (NORTHERN SPAIN)

Sediment cores of four boreholes (length from 9 to 27 m), retrieved in the Nalón estuary (Asturias, north of Spain), were investigated to assess the historical human footprint on the sedimentary sequence. Analytical measurements of grain-size, geochemical composition (major and trace elements) and stable Pb isotopic ratios were performed. Two different phases were identified throughout the sedimentary sequence by means of the Pb isotopic ratios. The upper sediment layer of the cores (variable depths between 3 to 9 m) showed a decrease of the 208Pb/206Pb ratios and an increase of the 206Pb/207Pb ratios whereas in the deep layers these ratios remained constant. These variations reflected additional nonatural inputs of Pb to the estuarine sediments which were identified from mining activities when the Pb composition of the different phases were compared to potential anthropogenic sources. A similar insight occurred with the variation of trace element concentration with depth. The enrichment factors of As, Hg, Pb, Sb and Zn related to the background values allowed to distinguish the impact of the intense human activity, mainly linked to the different mining activities developed in the region. Despite the decrease and closure of mining exploitations during the second half of the 20th century, results showed ongoing input of As, Hg, Pb, Sb and Zn to the coastal sediments. Thus, the legacy of contamination by these elements, mainly from leaching of slags and tailings dams, is still recorded in the estuarine sediments.