Geological record of extreme floods and anthropogenic impacts on an industrialised bay: the inner Abra of Bilbao (northern Spain)

The Bilbao estuary is one of the most polluted areas on the northern coast of Spain, owing to the direct disposal of urban effluents and waste waters from mining and industrial activities that has occurred during the last 170 years. Recent sediment records collected from the inner Abra of Bilbao bay were examined using a multidisciplinary 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 extreme weather events. Most contaminated materials are buried belowa thin layer (1–21 cm) of cleaner sediments which 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 events may endanger recently-achieved environmental improvements in historically contaminated coastal areas.This research was funded by Spanish MINECO (CGL2013-41083-P and RTI2018-095678-B-C21, MCIU/AEI/FEDER, UE), UPV/EHU (UFI11/ 09) and EJ/GV (IT976-16) projects. This is contribution 48 of the Geo-Q Zentroa Research Unit (Joaquín Gómez de Llarena Laboratory)