Recolonization of benthic infauna subsequent to capping of contaminated dredged material in East Sha Chau, Hong Kong

This paper presents the findings of a 3-year study upon the recolonization of infaunal macrobenthos following the cessation of disposal of contaminated sediment into dredged pits and capping of the pits with uncontaminated sediment. At reference sites, amphipods or polychaetes numerically dominated, while crabs dominated the biomass. There were significant temporal changes in abundance, which were attributable to either change in amphipod or polychaete abundance. The biomass, however, fluctuated only slightly over time. Three capped pits (CPA, CPB, CPC) all started with low biomass and abundance, and showed increase in both parameters over time. The increase in abundance ranged only from 1.0 to 2.3 times, whereas the increase in biomass ranged from 5.2 to 50.0 times. The final abundance and biomass at CPB were comparable to those at the reference sites. CPA and CPC had lower abundance than the reference sites, but the biomass was >15 times higher than the biomass at the reference sites. Small polychaetes numerically dominated all the three capped pits (58–79%), but the relative contribution of taxa to total biomass varied with the pits: molluscs dominated CPA (98%) and CPC (83%), whereas polychaetes (30%), crustaceans (27%), and molluscs (21%) dominated CPB. Our results indicate that benthos appear to have recolonized the capped pits; and there seem to be two recolonization patterns on the basis of biomass, one characterized by the dominance by molluscs and the other by the dominance by crustaceans and molluscs.