The significance of sediment contamination in a coastal wetland, Hong Kong, China

The Mai Po Marshes (Hong Kong), which bear an increasing pollution burden, are amongst the most threatened regional wetland habitats. Contamination of water and thus sediment may result in significant impacts upon the wetland ecology. Assessment of sediment contamination across the wetland is critical to understanding and managing the implications of water pollution. Sediment contamination in the wetland is shown to be high. A distinctive spatial distribution of contaminants was observed, in that sediments from the southern and northern ends of the wetland had significantly higher total nitrogen and total copper than other areas. Total phosphorus was more concentrated at the southern end, and total zinc was more enriched at the northern end of the wetland. The surface (0–8 cm) sediments had significantly higher total concentrations of phosphorus and zinc compared to the bottom (8–16 cm) sediments. These results indicate the significantly increasing pollution pressure from nearby industrial activities and urban expansion. The low water solubility (<10% of the total content) of all contaminants suggests that they may not be readily mobilised across the sediment-water interface. This would also explain the low or non toxic results of sediment elutriate toxicity tests on luminescent bacteria.