Experimental simulation of the effects of macrobenthos on the microcycling of nitrogen in the Yangtze estuarine and tidal flat ecosystem

Based on the natural distribution of macrobenthos, two sections typical of the eastern tidal flat of Chongming Island and Xupu tidal flats were chosen as the study area in the Yangtze estuarine and coastal zone. Using a comparative and simulative approach, this study quantitatively explored the effects of macrobenthos (Ilyoplax deschampsin and Corbicula fluminea) on the exchange of nitrogen across the sediment-water interface and the early diagenesis of nitrogen in tidal sediments from the Yangtze Estuary. It was found that Ilyoplax deschampsin and Corbicula fluminea affected the exchange of nitrogen across the sediment-water interface by different biological mechanisms. Ilyoplax deschampsin enhanced the exposed area of sediment to water and air by its bioturbation. It therefore accelerated the exchange of nitrogen at the sediment-water interface. Compared with Ilyoplax deschampsin, Corbicula fluminea, however, influenced the exchange of nitrogen across the sediment-water interface mainly by the physiological mechanisms such as excretion. Crabs such as Ilyoplax deschampsin changed the physical structure of the tidal sediments through intense bioturbation, and increased the content of dissolved oxygen in the sediments by increasing the exposure of these sediments to air. As a consequence, the processes of biogeochemical cycling of nitrogen (e. g. ammonification and nitrification) were markedly accelerated in the estuarine and tidal sediments. Corbicula fluminea is mainly round in tidal surface sediment. It affected nitrogen cycling in the surface sediments mainly by physiological activities such as the excretion. In addition, it was also found that the burrowing of Corbicula fluminea, to some extent, had a potential influence on the nitrogen cycling.