Benthic nutrient fluxes in the intertidal flat within the Changjiang (Yangtze River) Estuary

In an annual cycle from March 2005 to February 2006, benthic nutrient fluxes were measured monthly in the Dongtan intertidal flat within the Changjiang (Yangtze River) Estuary. Except for NH₄ ⁺, there always showed high fluxes from overlying water into sediment for other four nutrients. Sediments in the high and middle marshes, covered with halophyte and consisting of macrofauna, demonstrated more capabilities of assimilating nutrients from overlying water than the low marsh. Sampling seasons and nutrient concentrations in the overlying water could both exert significant effects on these fluxes. Additionally, according to the model provided by previous study, denitrification rates, that utilizing NO₃^- transported from overlying water (D_W) in Dongtan sediments, were estimated to be from -16 to 193 μmol h^-1 m^-2 with an average value of 63 μmol h^-1 μm^-2 (n=18). These estimated values are still underestimates of the in-situ rates owing to the lack of consideration of D_N, i.e., denitrification supported by the local NO₃^- production via nitrification.