Distribution of river-borne particulate Pb in the Basque continental shelf (Bay of Biscay)

The Sediment, Oil spill and Fish Tracking model (SOFT) was used to simulate the river-borne particulate Pb dispersion and sedimentation in the Basque continental shelf (BCS). In this case, SOFT used 3D current fields obtained with the Regional Ocean Modeling System (ROMS). From the SOFT results, connectivity matrices were obtained to analyze source-sink relationships. Considering the studied 12 rivers, the Ibaizabal River is the major contributor, accounting for 69 % of the total particulate Pb release. On a yearly basis, Pb accumulates mostly in the West sector of the BCS. The differences between the observations for the 2000–2011 period and the modeling results could be due to the fact that SOFT used climatological information on currents and discharges from the Basque rivers (the Adour River was not included) and did not estimate the resuspension process. To improve the results, the SOFT outputs together with Hs12 data (significant wave height exceeding 12 h per year) and observed sedimentary Pb concentrations were integrated into a Geographic Information System (GIS) environment to adopt a multivariate approach. At the BCS spatial scale, the combination of numerical models and GIS-assisted statistics did not provide an accurate prediction of the distribution of river-borne particulate Pb accumulation. At smaller scales, areas influenced by the inputs of Basque rivers and others affected by additional factors (i.e., dredged material disposal activities, contributions from neighboring rivers and sub-grid scale transport processes) were identified. Under the current European marine legislative framework, the improved knowledge obtained on river-borne particle dispersal dynamics can assist the assessment of the marine contamination from the local to the regional scale.