Assessing pollution levels in sediments of a harbour with two opposing entrances. Environmental implications

The harbour of Ceuta, North Africa, differs substantially from conventional harbours with only one entrance since it has two opposing entrances and a channel which increases water renewal and local currents, with implications for sedimentary processes, levels of pollution and oxygen concentration. The distribution of heavy metals, nutrients and total hydrocarbons was investigated in sediment samples from this particular harbour. The grain size effect, a normalization technique using Fe concentrations and different sediment quality guidelines are discussed, and the data from the harbour of Ceuta are compared with other harbours worldwide. In spite of the water renewal, sediments inside the harbour of Ceuta were characterised by moderate levels of pollution, mainly hydrocarbons (496-6972 μg/g), P (282-1350 μg/g), N (100-2600 μg/g) and heavy metals Cu (5-865 μg/g), Pb (10-516 μg/g), Zn (296-695 μg/g), Cr (13-381 μg/g) and Ni (8-671 μg/g). Taking into account that there is no industrial activity around the harbour of Ceuta, the major sources of contamination are the sewage effluents of urban influence, antifouling paints and accidental oil spills during loading and dumping involved in shipping operations. The design of Ceuta harbour should be taken into consideration in the design, construction and management of future harbours.