Geological Record of Extreme Floods and Anthropogenic Impacts on an Industrialised Bay: The Inner Abra of Bilbao (Northern Spain)

Abstract

The Bilbao estuary is one of themost polluted areas on the northern coast of Spain, owing to the direct disposal of urban effluents and wastewaters frommining and industrial activities that has occurred during the last 170 years. Recent sediment records collected fromthe inner Abra of Bilbao baywere examined using amultidisciplinary approach including geochemical,micropaleontological and isotopic proxies to evaluate heavy metal contamination (Pb, Zn and Cd), ecological condition (benthic foraminifera), and sediment accumulation variability (210Pb). Results evidenced the interplay of both human activities and extremeweather events.Most contaminatedmaterials are buried belowa thin layer (1?21 cm) of cleaner sedimentswhich have been deposited since contaminant discharges have substantially decreased, due to industrial reconversion and environmental regulations. However, the fingerprint left in the sedimentary record by the catastrophic floods of 1983 confirms the potential of natural events for sediment relocation, showing catastrophic eventsmay endanger recently-achieved environmental improvements in historically contaminated coastal areas.