Contents lists available at ScienceDirect Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul Baseline Environmental regeneration processes in the Anthropocene: The Bilbao estuary case (northern Spain) María Jesús Irabien a, ⁎ , Alejandro Cearreta b , Humberto Serrano b , Víctor Villasante-Marcos c a Departamento de Mineralogía y Petrología, Universidad del País Vasco UPV/EHU, Apartado 644, 48080 Bilbao, Spain b Departamento de Estratigrafía y Paleontología, Universidad del País Vasco UPV/EHU, Apartado 644, 48080 Bilbao, Spain c Observatorio Geofísico Central, Instituto Geográfico Nacional, C/ Alfonso XII, 3, 28014 Madrid, Spain ARTICLE INFO Keywords: Metals Magnetic susceptibility Benthic foraminifera Sedimentary record Environmental management Bilbao estuary ABSTRACT This work tackles a multidisciplinary study on the recent sedimentary record of the Bilbao estuary (northern Spain), which is the backbone of a city that was primarily industrial and now is widely recognized as a successful example of urban transformation. Although hotspots of heavily polluted materials still remain at the mouth of the two main tributaries (Galindo and Gobelas), the data obtained confirm the ongoing formation of a new layer of sediments (here called “postindustrial zone”) covering historically polluted and azoic deposits. It is char- acterized by largely variable levels of metals and magnetic susceptibility and moderate-to-high abundances of benthic foraminifera. Monitoring of the evolution of this layer appears a key factor to assess environmental improvement and decision-making in polluted estuaries. It is increasingly recognized that both marine and continental sys- tems dominated by planet Earth drivers (climate, volcanic events, eu- static processes, etc.) are now also controlled by social and economic factors such as human population growth and industrialization (Meybeck, 2003). The widespread evidence of anthropogenic impact and its fingerprint left in the geological record has led the scientific community to discuss the advisability of defining a new geological time (the Anthropocene epoch) and the proposal of adding it to the Inter- national Chronostratigraphic Chart (Waters et al., 2016). We consider the Anthropocene epoch as starting from the mid-20th century (after Zalasiewicz et al., 2015). In this scenario of worldwide environmental transformation, coastal environments appear as the most threatened ecosystems. During the last decades, there has been a notable growth in research publication outputs not only on estuarine pollution (Sun et al., 2012) but also on environmental recovery (Duarte et al., 2015; Verdonschot et al., 2013). At present, there are numerous studies that monitor the chemical and ecological evolution with time in many es- tuaries of the world, and the results indicate that quality levels often improve when pollutant loading rates significantly decrease (Borja et al., 2016; Peng et al., 2015; Stein and Cadien, 2009). However, it is well known that persistent chemicals such as heavy metals, polyciclic aromatic hydrocarbons (PAHs), and halogenated hydrocarbons tend to accumulate in sediments, and data from dated sediment cores confirm that together with the increase in the variety of contaminants, a distinct decrease in the concentrations of common anthropogenic pollutants was observed in the last three decades (Heim and Schwarzbauer, 2013). This study is focused on the Bilbao estuary (northern Spain), which shares a similar history of environmental transformation since the Industrial Revolution with other estuaries of the most developed countries. The main aim of this work is to provide insight, through a multidisciplinary, high-resolution approach involving geochemical (heavy metals), physical (magnetic susceptibility), and micro- paleontological (foraminiferal assemblages) proxies, into how general improvements in quality inferred from long-term monitoring surveys of surface materials have an effect on the bottom sedimentary deposits. The information obtained allows the identification of areas of priority interest (hot spots of pollution), assessment of the current status of environmental regeneration of the estuary, and the choice of suitable management strategies. The Bilbao estuary is located on the northern coast of the Iberian Peninsula, in the inner Bay of Biscay (43°23′-43°14′N, 3°07′-2°55′W) (Fig. 1). It is also known as the Nervión estuary and exhibits mesotidal characteristics (average tidal variation 2.5 m, range 1 m at neap tides to 4.5 m at spring tides) and a mean river flow of 25 m 3 s- 1 (Leorri et al., 2008). Its recent history of transformation has been closely related to the exploitation of local Fe ores and the subsequent industrial and urban development. Since the first iron and steel industry was con- structed on reclaimed saltmarshes in 1854, all the original estuarine https://doi.org/10.1016/j.marpolbul.2018.08.022 Received 11 May 2018; Received in revised form 6 August 2018; Accepted 8 August 2018 ⁎ Corresponding author. E-mail addresses: mariajesus.irabien@ehu.eus (M.J. Irabien), alejandro.cearreta@ehu.eus (A. Cearreta), humberto.serrano@ehu.eus (H. Serrano), vvillasante@fomento.es (V. Villasante-Marcos). Marine Pollution Bulletin 135 (2018) 977–987 0025-326X/ © 2018 Elsevier Ltd. All rights reserved. T