Phosphorus Release Kinetics from Native P-Starved Raphidocelis subcapitata: Interactions Between Up and Downstream Sediments and Wetland Soils

Quantifying phosphorus (P) release from wetland soils into overlying water is essential for predicting eutrophication risks. This study investigated the kinetics of P release from upstream and downstream river sediments and wetland soils and assessed its bioavailability using a standard algal ( Raphidocelis subcapitata ) assay. Rate parameters derived from the power function, parabolic diffusion, and Elovich models were strongly correlated with algal growth, highlighting the role of P in downstream and wetland eutrophication. The relationship between 0.5 M NaHCO ₃ -extractable P and algal growth increased from R ² = 0.65 at the start to R ² = 0.95 by the end of the experiment, while 0.5 M NaOH-extractable P showed strong correlations with kinetic model parameters. The two-site first-order kinetic model effectively described the trends in P release, revealing distinct mechanisms controlling P mobilization. High correlations (R ² = 0.95) between algal growth and P bioavailability underscore the potential for eutrophication. The strong association between predicted P release and NaOH-extractable P suggests that moderately labile P pools play a key role in long-term nutrient availability. These findings demonstrate spatial variability in P release rates across sediments and wetland soils and emphasize the importance of wetland soils as potential long-term P sources. The continuous release of phosphorus from these soils may sustain or exacerbate eutrophic conditions, informing future nutrient management and wetland restoration efforts.