| In order to investigate the influence of sediment physical and chemical characteristics on the vertical distribution of NH+4, PO3-4and NO-3 and their diffusive fluxes at sediment-water surface, pore water equilibrators(Peeper) were employed to obtain multiple pore water profiles from reed and bulrush sediments in Lake Nansihu wetland. The results showed that sediment properties in the planted reed and bulrush fields, i.e. water content, porosity, KCl-extractable NH+4and NO-3were generally greater than those in seldom vegetation, and the porosity in 2-5 cm depth subsurface sediments increased by 57.5%, 34.6%, respectively. Nutrient profiles of NH+4and PO3-4at sediment-water interface exhibited a nearly exponential increase with increasing depth including a concentration maximum at a 8 cm depth, where there was a spike in the NH+4and PO3-4concentration. The diffusive flux (Jx) across the sediment-water interface could be calculated from Fick’s first law. The flux calculations showed reed could effectively decreased NH+4diffusive flux, and the NH+4diffusive flux, the maximum flux 3.57-4.48 mg/(m2·d) in reed field, was nearly three times greater than the minimum flux 0.90-1.24 mg/(m2·d) in seldom vegetation. However, there was a narrow PO3-4flux range from 0.02 to 0.04 mg/(m2·d) in three fields while NO-3 concentration gradient showed an opposite pattern and diffusive flux occurred in one direction from the overlying bottom water to the sediment pore water. The correlative results suggested that extractable nutrient contents in sediments correlated with pore water content, therefore, controlling extractable nutrient contents appeared to a viable measure to avoid nutrient recontamination to overlying water in wetlands. |
