Sources and sinks of sediment-bound contaminants in the Gulf of Lions (NW Mediterranean Sea): A multi-tracer approach

Abstract

Surficial sediments collected in 2002 throughout the Gulf of Lions continental shelf (NW Mediterranean) were analysed for trace metals (Cd, Co, Cr, Cs, Cu, Ni, Pb, Sr, Zn and Zr), major elements (Al, Ca, Fe, P and Ti) and the sewage marker coprostanol. In addition, particle size distribution, organic carbon (OC) and carbonates were also determined. Results showed that the metal contamination (Cd, P, Cu, Pb and Zn) is mainly introduced by the local rivers and accumulates-via a regulation by OC and silt fraction (2-63 mm)-in the direct vicinity of the mouths, in high shear stress environments. Here also the signal of sewage contamination is the best preserved, especially off the eastern point sources where local sedimentation rates save the faecal marker from biodegradation processes. It is demonstrated that the shallow prodeltas are the first repository areas for land-derived particles, exposing local ecosystems to both inorganic and organic contaminations. When going seaward, however, sediment dilution, particle sorting and biodegradation processes make that most riverborne contaminants rapidly reach natural levels. Only some metals (i.e. Pb and Zn)-closely associated with the clay fraction-still depict anthropogenic enrichment, which seems to be inherited from man-made aerosols.

Flux and composition of settling particles across the continental margin of the Gulf of Lion: the role of dense shelf water cascading

“…Mean composition of the non-siliciclastic fraction was 30.0% of CaCO 3 , 3.2% of OM, and 1.5% of opal (Fig. 5), quite similar values than those reported by Heussner et al (2006) during maximum fluxes over a 8-year period (31-32% CaCO 3 , 2% OM, and 1% opal), and close to the composition of the superficial sediments from the shelf and upper slope (31% CaCO 3 , 1-4% OM, and opal nearly absent or below the detection limits, Roussiez et al, 2006). (Table 2).…”

“…The concomitant wave height and southwestern river flow increase in late January 2006 (Fig. 2a, c) suggest the arrival of land-derived sediments, mainly from the Pyrenean rivers as suggested by the lower content in carbonates (Roussiez et al, 2006). Indeed, fast transport from the shelf to the slope was suggested by inside Lacaze-Duthiers canyon and by Palanques et al (2008) during the 2004/05 event when storms and DSWC coincide.…”

External forcings, oceanographic processes and particle flux dynamics in Cap de Creus submarine canyon, NW Mediterranean Sea

“…Furthermore, during these events, the non-siliciclastic fraction was close to the values reported by Heussner et al (2006), with ∼ 20-30 % CaCO 3 , 2-3 % OM, and opal was virtually absent. These values were also close to those reported by Roussiez et al (2006) for the superficial sediments from the shelf and upper slope (31 % CaCO 3 , 1-4 % OM and opal nearly absent or under detection limit).…”

Trace elements in different marine sediment fractions of the Gulf of Tunis (Central Mediterranean Sea)

“…There is no direct relationship between trace element concentrations and sediment properties, these results are in agreement with those found in other Mediterranean coastal zones such as the Gulf of Lions (NW Mediterranean Sea) (Roussiez et al, 2006;Sabatier et al, 2010). Trace elements concentrations present weak correlation to TOC, as was observed in surface sediments in a previous study carried out in the Gulf of Tunis (Essonni, 1998).…”