Han Wang

The incubation experiments focused on altering concentration gradients of nitrogen between sediment and overlying water to examine the diffusion flux of ammonium-nitrogen (NH₄⁺) and nitrate-nitrogen (NO₃^-) at sediment-water interface. In this study, the diffusion flux can be estimated based on calculating the average of the net change rate of nutrient concentrations in the overlying water. For the incubation experiment of different TN concentrations in the sediment, the results showed that the diffusion flux of ammonia at sediment-water interface is -52.57~84.57 mg·m^-2·d^-1, and for nitrate diffusion flux, the changing range during the incubation experiment is -110.13~143.25 mg·m^-2·d^-1. For the incubation experiment of different nitrogen concentrations in the overlying water, the results of NH₄⁺-N diffusion flux in L, M, H treatment were 3.37, -4.94, -3.84 mg·m^-2·d^-1, respectively. And the average diffusion flux of nitrate in L (0 mg NO₃^--N, 0 mg NH₄⁺-N), M (0.5 mg NO₃^--N, 1.5 mg NH₄⁺-N) and H (1 mg NO₃^--N, 2.5 mg NH₄⁺-N) treatment were 12.30, 10.39 and 7.11 mg·m^-2·d^-1. Results highlighted that concentrations gradient of nutrients were indeed an important factor affecting the diffusion flux at sediment-water interface. In addition, the diffusion of nutrients at sediment-water interface in aquatic ecosystem is not only controlled by concentration gradients, some other factors such as incoming water, hydrodynamics, dissolved oxygen content, sediment structure, biological disturbance, horizontal migration and diffusion of nutrients and turbulent diffusion caused by wind and wave, are equally important.