Characterization of Suspended Particulate and Sedimentary Phosphorus in a Large Urban-Core Wetland: Speciation, Cycling, and Release Risk

Phosphorus (P) in urban wetlands can be stored in both suspended particles and surface sediments, but the link between these two fractions remains not clear. In this study, we examined P species, sediment P release risk, and environmental factors at 24 sites in Haizhu Wetland, an urban-core wetland in Guangzhou, China. Suspended particulate P accounted for 50.5% ± 17.9% of total P, showing that suspended particles were an important short-term carrier of P. Iron-bound P was the dominant fraction in both suspended particles and sediments, accounting for 39.1% ± 7.7% and 35.7% ± 9.7% of total extracted P, respectively. Exchangeable P was the smallest fraction (2.9% ± 1.4% and 2.5% ± 2.1%). Redundancy analysis identified total dissolved solids, turbidity, and oxidation–reduction potential as the main variables associated with suspended P variation. Adsorption experiments showed that the equilibrium phosphate concentration at zero net P exchange ranged from 0.002 to 0.570 mg L–1, while the degree of P saturation ranged from 0.63 to 0.96. Exploratory structural equation modeling was consistent with an adsorption-related link between suspended particulate P and sediment P. These results suggest that P control should target short-term particulate P peaks and long-term sediment P stabilization in urban wetlands.