Ecosystem Developed in Artificial Tidal Flat Made by Mixture of Sand and Dredged Soil

This research was carried out to investigate effects of dredged soil (DS) addition to artificial tidal flat sediment on the emerging benthic ecosystem via this amendment of silt & clay content. Prior to use, DS was treated with poly aluminium chloride (PAC) or a paper sludge-derived agent (PS) for coagulation or solidification for ease of its treatability, whereas dewatered DS was also prepared without any treatment. These DSs were respectively mixed with mountain sand to attain 25% of silt & clay content on the basis of inorganic component, and then the mixtures were used for construction of artificial tidal flats. In the control experiment, natural tidal flat sediment with the same silt & clay content was used. The total wet-weight and number of macrobenthos in the artificial tidal flats were larger than those in the control tidal flat, while polychaetes Capitella sp. and a gastropod Batillaria cumingii were the dominant species in the constructed tidal flats. These results confirmed the feasibility of using DS as an additive of silt and clay to improve benthic ecosystems in constructed tidal flats. In use of DSs treated with PAC and PS, negative impact by these agents was not observed on the number and species of emerging macrobenthos.