Impact of macrofaunal activities on the DIN exchange at the sediment-water interface along the tidal flat of Yangtze river estuary

The macrofaunal activities exert intensive and extensive influences on the accumulation, transportation, exchange and geochemistry processes of pollutants and redox sensitive elements around the sediment-water interface. Based on the simulated and contrastive analysis method, effects of bivalve Corbicula fluminea activities on dissolved inorganic nitrogen (DIN) exchange between sediment-water interface in different experimental conditions and nitrogen biogeochemical cycling along the tidal flats of Yangtze River estuary are discussed. In short time experiment, Corbicula fluminea burrowing activities increased NH₄⁺ release from sediments, and NO₃^- efflux to overlying water was much more in Corbicula fluminea inhabiting core. During long time incubation, NH₄⁺ and NO₃^- released in turn from the sediments, bioturbation can facilitate NH₄⁺ release from the sediments at the beginning of incubation, and stronger nitrification derived from bioturbation within the sediments enlarge NO₃^- concentration. Disturbance and bioirrigation of Corbicula fluminea can accelerate organic matter mineralization and NH₄⁺ exchange between overlying water and pore water, result in a larger release from NH₄⁺ pool in top-sediment to overlying water. In conclusion, by means of excretion, burrowing, bioirrigation and bioturbation, Corbicula fluminea activities can evidently modify the nitrogen dynamics in sediment-water system.