RESUMO
Wetland type plays an important role in controlling the phosphorus (P) biogeochemical cycle, while its effect on labile P dynamics and coupling with iron (Fe) and sulfur (S) in coastal wetlands remains unclear. In this study, chemical sequential extraction and high-resolution diffusive gradients in thin-film (DGT) techniques were employed to investigate P forms, mobilization, and labile Fe-S-P coupling in several coastal wetland types [i.e., natural wetland (NW), aquaculture pond (AP), artificial (ARW) and natural restored wetlands (NRW)]. Compared with NW, AP decreased the total P by 40.6%. The concentrations of soil organic P and inorganic P (including NaOH-extractable P and HCl-extractable P) were significantly increased in ARW, but decreased in AP and NRW. DGT-labile P, Fe, and S concentrations changed significantly in different wetland types, and the labile P concentrations in AP were significantly higher than those in the others. Similar spatial distribution dynamics and significant positive relationships between labile P, Fe, and S concentrations in NW and AP confirmed that intense reduction in iron and sulfate are the key mechanisms regulating P mobilization. However, these relationships were decoupled in restored wetlands, suggesting that the Fe redox-coupled P mobilization and sulfate reduction were sensitive to wetland changes. The diffusion fluxes of P across the soil-water interface were positive in AP (0.619 pg·cm-2·s-1), indicating that P was released from soil to the overlying-water. We concluded that coastal wetland types altered soil P forms, availability, and labile Fe-S-P coupling, and the natural restored wetland could help stabilize the soil P pool and eventually controlled the mobilization and release of P.