Heavy metals in particulate matter and sediments in the southern Barcelonasedimentation system - (North-western Mediterranean)

Concentrations of selected heavy metals (Cr, Cu, Ni, Pb and Zn) from surfac e sediments, suspended particulate matter and settling particles in the sou thern Barcelona continental margin were studied in order to evaluate the en vironmental impact of the anthropogenic metals discharged by the Llobregat River in this Mediterranean area. The temporal variation of heavy metals di scharged by this river onto the continental shelf is clearly related to the river water flow. Part of the fine sediment and associated heavy metals tr ansported by the Llobregat River during periods of low river flow accumulat e on the river bed, and they are totally removed and discharged onto the Ba rcelona continental shelf during sporadic river water flow increases. Metal s produce significant anomalies of chromium (X 2.5), copper (X 3.4) and zin c (X 3.7) in the surface sediments of the Llobregat prodelta and tend to be transported along the continental shelf following the mean flow. Metals as sociated with the finest suspended flocs transferred to the slope are contr olled by the shelf-slope density front and are transported along slope by t he general geostrophic current, instead of accumulating and becoming concen trated in the slope bottom sediments. Settling particulate matter collected in sediment traps on the Barcelona continental slope offshore of the shelf -slope front shows low heavy metal concentrations except in a few sediment trap samples that are significantly metal-enriched in chromium (X 4.5) and zinc (X 6.8). This enrichment is associated with very short and sporadic ri ver flow increases and is only recorded inside the Foix submarine canyon, w hich acts as a preferential conduit for the shelf-slope sediment transfer. (C) 1999 Elsevier Science B.V. All rights resented.