Storage capacity and releasing risk assessment of phosphorus in soils from restored wetland in the Yellow River Delta, China

The application of wastewater is a method used for the restoration of degraded wetlands in the Yellow River Delta (YRD). However, the sediments may become a secondary pollution source, when P is saturated in the restoration process. By means of the diffusive gradient in thin-film (DGT) technology and modified sequential fraction method, the present study investigated the phosphorus (P) storage capacity and release potential of the wetland after 9 years of restoration. The results showed that the concentration of total P (P t ) ranged from 578.3 to 678.8 mg kg -1 in soils. The highest fraction of P was Dil.HCl-Pi (mean,74.1-78.7%)，whereas the lowest was NaHCO 3 -Pi (mean, 0.4-1.3%). Each form of P in the soil basically decreased with depth and accumulated more in the 0-40 cm profile. The concentrations of soluble reactive P (SRP) in the overlying water were higher than those in the interstitial water. The critical P concentration of the wetland sink-source conversion was 0.52 mg L -1 . These results showed that each form of P showed a vertical decrease with depth in the soil column. Significant differences were observed among the average concentrations of P t  as well as the P i  values at each site. The concentrations of P t and P i in site A were significant higher than those in other sites. SRP showed no obvious difference in overlying water and interstitial water with seasonal changes. The P-retention capacity of the wetland was quantitatively evaluated using PSI and DPS parameters. The wetland still had sink capacity after 9 years of wastewater restoration. This research enriches theories of domestic wastewater remediation in wetlands and provides an important theoretical basis for using domestic wastewater to repair degraded wetlands in the YRD.