Water Renewal Time and Trace Metal Concentration in Civitavecchia Port (Rome), Italy

Most of the harbours can be considered as semi-enclosed areas where water stagnation leads to physical and chemical alterations due to anthropogenic activities. These features affect the quality of the port waters as well as the environmental health of coastal ecosystems in the surrounding areas. In order to understand the potential degradation of water quality within the harbour area it is essential to evaluate the hydrodynamic behaviour of the system. In this study, the DELFT3D-FLOW model, which allows to estimate the three-dimensional field velocity, was used to spatially characterize the water renewal time within the harbour. In particular, the flushing time (FT), which represents the time required for the total mass of a conservative tracer originally within the water body to be reduced to a factor 1/e, was examined. The concentration of contaminants in sediments is indeed a proper parameter to test the reliability of the calculated water renewal time within the semi-enclosed basins, since it relies on time-integrated measurements compared to single observations of water column. This research aims at studying the relation between the FT and the pollution due to trace metals in marine sediments. For this purpose, surface sediment samples were collected along a series of stations located in the innermost part and near the mouth of the Civitavecchia harbour. As, Cr, Hg, Ni, Cu, zn, Pb and Al concentrations were analysed to calculate the enrichment factor, which provides an estimate of the heavy metal contamination in the harbour surface sediment. The obtained results show a high correlation between the FT and the enrich- ment factor within the Civitavecchia port, confirming that water renewal can be used as an indicator of water quality degradation in semi-enclosed areas.