Elsevier

Progress in Oceanography

Volume 163, April 2018, Pages 161-171
Progress in Oceanography

Chronology and sources of trace elements accumulation in the Rhône pro-delta sediments (Northwestern Mediterranean) during the last 400 years

https://doi.org/10.1016/j.pocean.2017.01.008Get rights and content

Highlights

  • Trace elements are accumulated in the Rhône prodelta sediments.

  • Preindustrial sediments recorded floods and channelization of the Rhône River.

  • Contamination reached a maximum between 1970 and 1980 CE.

Abstract

The Rhône pro-delta sediments receive the particulate inputs from the Rhône River, the largest freshwater discharge of the Western Mediterranean Sea. Trace element (TEs: Ag, Cd, Co, Cr, Cu, Ni, Pb, and Zn) concentrations and stable Pb isotope ratios were determined along a 7.7-m-long sediment core collected from the Rhône prodeltaic lobe, archiving the deposits of the last 400 years. Trace element mean concentrations during the pre-industrialized era (before 1850 CE) were no different from the average composition of Earth’s upper crust, except for Cr. Principal component analysis, performed on TEs and tracers, suggests three origins for TEs that we identified as (i) marine biogenic material (Ag, Cd), (ii) ultramafic rocks (Li, Cr, Ni), and (iii) other clay minerals (Co, Cu, Pb and Zn). During the pre-industrial period, several changes in the TE/Al ratios coincided with flood events or/and modifications in the channelization of the Rhône River mouth. Some frequencies in the TEs temporal variations allow us to hypothesize some influence of climate variation. Sediments deposited after 1850 CE exhibited concentrations of certain TEs exceeding 1.3–3.5 times the concentrations of the pre-industrial era (Ag > Cd-Pb > Cu-Zn). Principal component analysis, performed on post-1850 CE data, allows to distinguish pristine and “anthropogenically impacted” TEs. Pristine TEs, such as Co, Cr, and Ni, are linked with clay markers (Al, Li and Fe), Co and Ni are associated with Mn-enrichment, whereas Cr is correlated with Fe. “Anthropogenically impacted” elements consist of Ag, Cd, Cu, Pb, and Zn. Vertical profiles show that TE contamination has increased dramatically after the IInd World War and reached a maximum between 1970 and 1980, consistently with anthropogenic atmospheric emissions changes. Sediment deposited on the Rhône prodelta at the beginning of XVIIth Century have 206/207Pb ratios close to values of natural Pb (1.200), whereas sediments deposited after 1850 CE are clearly contaminated by European gasoline and industrial Pb pools (<1.180). In addition, peak-events can be related to flooding periods, natural and man-induced channelization of the Rhône River mouth, or diagenetic processes.

Introduction

As stated by the international Geotraces program (www.geotraces.org), many trace elements (TEs) are critical for marine life, and therefore influence the functioning of ocean ecosystems and the global carbon cycle. Indeed, they are micronutrients essential to life (e.g., Fe, Zn, Cu), tracers of modern processes in the ocean (e.g., Al, Mn), and are significantly perturbed by human activities (e.g., Pb). In the Western Mediterranean, the biogeochemical cycling of TEs is largely governed by atmospheric inputs (Migon et al., 2002). However, the influence of rivers on TE distributions is discernible in the sediments of the adjacent continental shelf (Ferrand et al., 1999, Roussiez et al., 2005, Roussiez et al., 2006, Radakovitch et al., 2008). According to the Mermex Group review (The Mermex Group, 2011), present and past inputs of riverine particulate TEs to the Mediterranean, especially anthropogenic TEs, need to be more precisely estimated.

Estuary and delta sediments are suitable environments to reconstruct historical accumulation of elements and anthropogenic chemicals from continental and marine sources during last centuries or even millennia (e.g., Valette-Silver, 1993, Santschi et al., 2001, Callender, 2003). In particular, this is the case for the Rhône prodeltaic prism, which receives particulate inputs from the Rhône River (RR), and has archived its inputs for centuries (Fanget et al., 2013). Studying this area provides a unique opportunity to document the chronology and the sources of the TE inputs from the largest riverine sediment source to the Mediterranean Sea.

Here, we document the temporal accumulation of TEs (Ag, Cd, Co, Cr, Cu, Ni, Pb and its stable isotopes, and Zn) in sediment recovered in the Roustan lobe within the Rhône prodelta area, located on the continental shelf of the North side of the Western Mediterranean (Fig. 1). Based on a multiproxy study, including major elements and radiometric analyses, we have been able to identify the major changes in TE accumulation in the Rhône prodelta sediments during the last four centuries. These changes are discussed in terms of hydrological regime, channelization of the RR mouth, climate change, and TE contamination history.

Section snippets

Study area

The RR and its tributaries drain various catchments including sedimentary rocks, granitic, and metamorphic rocks from the Alps, Massif Central, and Vosges. In addition, RR carries alluvium from one of the most industrialized and urbanized European catchments (The Mermex Group, 2011). The RR sediment load has varied significantly during the past few centuries Since the XIXth Century, it has decreased by a factor close to ten, mainly because of stabilization of mountain slopes due to decline of

Core collection

This study is based on a multi-proxy analysis of a 7.71 m-long piston core (KS57, Fig. 1) collected on the Roustan prodeltaic lobe (43°17.10′N; 4°50.97′E) at 79 m water depth during the Rhosos cruise in September 2008 aboard R/V Le Suroît. The core was sliced every 2 cm from 2 cm below the sediment-water interface (SWI) to 100 cm, then every 4 cm down to the bottom of the core, which was 767 cm below the SWI. Subsamples were frozen (−18 °C), freeze-dried and stored under cold (4 °C) and dark conditions

Characterization of sediment core

The dating of core has been established based on 210Pb, 137Cs vertical profiles and microfossil assemblages (ostracods, benthic foraminifera, and coccoliths) in combination with sedimentological proxies (Fanget et al., 2013). Herein, we present our geochemical results based on this well-constrained chronology. This 7.67 m core covers a period of just over 400 years. The first 3.75 m below the SWI has accumulated since the middle of the XIXth Century, corresponding roughly to the beginning of the

Summary and conclusions: The Rhône prodelta anthropization in the context of Mediterranean Sea

Trace element concentrations in surface coastal sediments are largely documented in the Western Mediterranean and the Eastern Mediterranean (e.g., Scoullos and Oldfield, 1986, Abdel-Moati and El-Sammak, 1997, Abi-Ghanem et al., 2009, Abi-Ghanem et al., 2010, Schintu et al., 2009, Schintu et al., 2015, Mzoughi and Chouba, 2011, Roussiez et al., 2011). Concentrations range between geological backgrounds, with the example of Sardinia coasts (Schintu et al., 2009), and very high concentrations. In

Acknowledgements

We thank the scientific team as well as the captain and crew of the cruise RHOSOS-2008 cruise on board R/V Le Suroît. This study was carried out as a part of the WP3 Mermex/Mistrals and is a contribution to the international LOICZ projects. This work was partly supported by the European project Hermione (FP7-ENV-2008-1-226354) and ANR (France) EXTREMA (contract number ANR-06-VULN-005). We are grateful to O. Radakovich for his comments on the manuscript.

References (88)

  • F. Eyrolle et al.

    Radiological consequences of the extreme flooding on the lower course of the Rhône valley (December 2003, South East France)

    Sci. Total Environ.

    (2006)
  • J.-L. Ferrand et al.

    Isotopic tracing of anthropogenic Pb inventories and sedimentary fluxes in the Gulf of Lions (NW Mediterranean Sea)

    Cont. Shelf Res.

    (1999)
  • A.J. Frierdich et al.

    Distribution and speciation of trace elements in iron and manganese oxide cave deposits

    Geochim. Cosmochim. Acta

    (2012)
  • A. García-García et al.

    Shallow gas off the Rhône prodelta, Gulf of Lions

    Mar. Geol.

    (2006)
  • L.-E. Heimbürger et al.

    Natural and anthropogenic trace metals in sediments of the Ligurian Sea (Northwestern Mediterranean)

    Chem. Geol.

    (2012)
  • Z.Z.A. Kuzyk et al.

    Inferences about the modern organic carbon cycle from diagenesis of redox-sensitive elements in Hudson Bay

    J. Mar. Syst.

    (2011)
  • M. Komarek et al.

    Lead isotopes in environmental sciences: a review

    Environ. Int.

    (2008)
  • G.M. Maillet et al.

    Morphological changes and sedimentary processes induced by the December 2003 flood event at the present mouth of the Grand Rhône River (southern France)

    Mar. Geol.

    (2006)
  • J. Martin et al.

    Recent accumulation of trace metals in sediments at the DYFAMED site (Northwestern Mediterranean Sea)

    Mar. Pollut. Bull.

    (2009)
  • C. März et al.

    Manganese-rich brown layers in Arctic Ocean sediments: composition, formation mechanisms, and diagenetic overprint

    Geochim. Cosmochim. Acta

    (2011)
  • C. Migon et al.

    Transfer of atmospheric matter through the euphotic layer in the northwestern Mediterranean: seasonal pattern and driving forces

    Deep Sea Res. I

    (2002)
  • J. Miralles et al.

    210Pb sedimentation rates from the Northwestern Mediterranean margin

    Mar. Geol.

    (2005)
  • J. Miralles et al.

    Atmospheric lead fallout over the last century recorded in Gulf of Lions sediments (Mediterranean Sea)

    Mar. Pollut. Bull.

    (2006)
  • J. Miralles et al.

    Radionuclide deposition in the Rhône River Prodelta (NW Mediterranean Sea) in response to the December 2003 extreme flood

    Mar. Geol.

    (2006)
  • N. Otero et al.

    Fertilizer characterization: major trace and rare earth elements

    Appl. Geochem.

    (2005)
  • A. Palanques et al.

    Historical record of heavy metals in a highly contaminated Mediterranean deposit: the Besos prodelta

    Mar. Chem.

    (1998)
  • D. Pont et al.

    Medium-term changes in suspended sediment delivery to the ocean: consequences of catchment heterogeneity and river management (Rhône River, France)

    Estuar. Costal Shelf Sci.

    (2002)
  • M. Provansal et al.

    The geomorphic evolution and sediment balance of the lower Rhône River (southern France) over the last 130 years: hydropower dams versus other control factors

    Geomorphology

    (2014)
  • O. Radakovitch et al.

    210Pb and caesium accumulation in the Rhône delta sediments

    Estuar. Costal Shelf Sci.

    (1999)
  • O. Radakovitch et al.

    Input of particulate heavy metals from rivers and associated sedimentary deposits on the Gulf of Lion continental shelf

    Estuar. Costal Shelf Sci.

    (2008)
  • S. Romano et al.

    Historical pattern and mass balance of trace metals in sediments of the northwestern Adriatic Sea Shelf

    Mar. Pollut. Bull.

    (2013)
  • V. Roussiez et al.

    Background levels of heavy metals in surficial sediments of the Gulf of Lions (NW Mediterranean Sea): an approach based on 133Cs normalization and lead isotope measurements

    Environ. Pollut.

    (2005)
  • V. Roussiez et al.

    Fate of metals in coastal sediments of a Mediterranean flood-dominated system: an approach based on total and labile fractions

    Estuar. Costal Shelf Sci.

    (2011)
  • F. Sabatier et al.

    Sediment budget of the Rhône delta shoreface since the middle of the 19th century

    Mar. Geol.

    (2006)
  • P.H. Santschi et al.

    Historical contamination of PAHs, PCBs, DDTs, and heavy metals in Mississippi River Delta, Galveston Bay and Tampa Bay sediment cores

    Mar. Environ. Res.

    (2001)
  • M. Schintu et al.

    Monitoring of trace metals in coastal sediments from sites around Sardinia, Western Mediterranean

    Mar. Pollut. Bull.

    (2009)
  • M. Schintu et al.

    Interpretation of coastal sediment quality based on trace metal and PAH analysis, benthic foraminifera, and toxicity tests (Sardinia, Western Mediterranean)

    Mar. Pollut. Bull.

    (2015)
  • M.J. Scoullos et al.

    Trace metal and magnetic studies of sediments in Greek estuaries and enclosed gulfs

    Mar. Chem.

    (1986)
  • X. Durrieu de Madron et al.

    Marine ecosystems’ responses to climatic and anthropogenic forcings in the Mediterranean

    Prog. Oceanogr.

    (2011)
  • C. Abi-Ghanem et al.

    Mercury distribution and methylmercury mobility in the sediments of three sites on the Lebanese coast, Eastern Mediterranean

    Arch. Environ. Contam. Toxicol.

    (2010)
  • M.A.R. Abdel-Moati et al.

    Man-made impact on the geochemistry of the Nile Delta lakes. A study of metals concentrations in sediments

    Water Air Soil Pollut.

    (1997)
  • G. Arnaud-Fassetta

    Dynamiques Fluviales Holocènes Dans Le Delta Du Rhône

    (1998)
  • Association Nazairienne de Généalogie. Epidémies et famines en France: Climat et épidémie....
  • S. Azoury et al.

    Historical records of Hg, Pb and PAH depositions in a dated sediment core from the Eastern Mediterranean

    Environ. Sci. Technol.

    (2013)
  • Cited by (0)

    1

    Present address: Aarhus University, Department of Geoscience, Høegh-Guldbergs Gade 2, DK-8000 Aarhus C, Denmark.

    View full text