The role of bottom sediment in pollution assessment of surface water and the problems related to its characterization were reviewed and identified. The importance of data validation in monitoring bottom sediment was recognized. The effect of grain size distribution and of spatial variations in the bottom sediment justified a sound sampling and analytical protocol.

Analysing the clay-silt fraction to reduce the effect of grain size was shown to be reliable. Before monitoring, however, one should prove that bottom sediment characteristics are homogeneous horizontally around the sampling site. Due to vertical sediment stratification from temporal variation of pollution, identification of the sediment layer to be monitored is of the utmost importance. It was found that “double sampling”, i.e., simultaneous sampling of the surface and the top 1 cm of the sediment layer provided representative data when redistribution of the bottom sediment is within acceptable limits. When characterizing the release of carbonate-bound phosphates and heavy metals from sediments, the multistage extraction technique with carbon dioxide was found to be effective. It was concluded that pollutant dynamics and the impact of the intertidal zones on the coastal marine ecosystem could be evaluated by monitoring the sediment, interstitial water, tidal creek and tidal waters simultaneously.

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