Recent influence of man on the Ebro margin sedimentation system, northwestern Mediterranean Sea

Abstract

Man's recent activities, such as construction of reservoirs, dams and irrigation channels, have changed the natural dynamics of the Ebro margin sedimentation system. The amount of sediment supplied by the Ebro river is presently less than 5% of the amount supplied 50–60 years ago. Suspended sediment supplied by the river at the present time has a higher proportion of clay minerals than before the construction of the dams and reservoirs. At present, only the finer particles escape the dams, leaving the remaining sediment and apparently a large proportion of heavy metal inputs coming from inland cities and industries trapped behind them. In the lower part of the river, heavy metal pollution in the suspended matter is relatively low. Heavy metal anomalies in the shelf muds suggest that present-day sedimentation is restricted mainly to the proximal mud-belt area, near the mouth of the river. Abnormally high concentrations of heavy metals in suspended matter have been detected at the shelf break and on the upper continental slope of the Ebro system. These polluted particles come from rivers and cities located north of the Ebro mouth and are transported by the general southward flow along the slope. Some pollutants can be used as tracers for particle dynamics on the Ebro margin. The present supplies and fluxes of suspended sediment are significantly different from those which occurred before management of the river and coast began.