"Safe" Sequestration of Additional Phosphorus in Freshwater Wetland and Salt Marsh at Coastal Zone in the Yellow River Delta

Coastal wetlands can intercept and retain P from upland sources, limiting excessive P into coastal water. However, factors like hydrologic management and vegetation variations on P retention or removal efficiency have been far from understood. In this study, the rhizosphere sediment and profile samples were collected under different vegetation cover from May to October in 2019 in the wetlands in Yellow River Delta. We used the concept of sediment P storage capacity (SPSC) to estimate the amount of P "sink" or P "source". The results indicated that the wetlands functioned as a significantly P "sink" because an elevated SPSC value was reported in restored wetland (70-104 mg kg(-1)) compared with that in non-restored wetland (55-79 mg kg(-1)). The increased SPSC value was mainly attributed to the significantly increase of sediment organic matter content in the restored wetlands as a result of freshwater restoration of the degraded wetlands. The vegetation cover with higher plant biomass production exhibited higher SPSC value while the SPSC showed no significant variation in different period of plant growth. The SPSC value significantly decreased with sediment depth (0-40 cm) whether the wetlands restored or not. The relatively long safe lifespan of wetlands indicated that the wetland substrate was less saturation and it can environmental friendly store additional P. However, further investigation need to elucidate the role of particulate inorganic phosphorus played in the SPSC calculation of these wetlands. In conclusions, the freshwater restoration provide higher sediment P storage capacity and deserved more application in the degraded wetlands.