Optimizing phosphorus release risk index based on river sediment physicochemical properties

Abstract

This study develops a framework to optimize the selection of phosphorus release risk indices (PRRIs) for river sediments, based on key physicochemical properties—organic matter (OM), redox potential (Eh), and the CDB-P/Ca-P ratio (ROP). To address variability in PRRI applicability across sediment types, sediments from six rivers in China’s Sichuan Basin were analyzed. Results show that universal indices—including the Eutrophication Risk Index (ERI), Soil Phosphorus Storage Capacity (SPSC), Degree of Phosphorus Saturation (DPS), and Phosphorus Sorption Index (PSI)—exhibit strong, significant correlations with phosphorus release fluxes across all sediment categories (r = 0.71–0.89, p < 0.01). Sediment classification further improves prediction accuracy: ERI and PSI perform best in OM-rich sediments (OM-1), where organic matter drives adsorption-desorption processes; Non-apatite inorganic P (NAIP) and Water-Soluble P (WSP) are reliable indicators in CDB-P-dominated systems (ROP-1); ERI is prioritized in weakly reducing sediments (Eh-2) (r = 0.90); and DPS, alongside Equilibrium P Concentration at net zero sorption (EPC₀), is more applicable in Ca-P-dominated sediments (ROP-2). This framework balances assessment accuracy and operational feasibility, offering actionable guidance for precise phosphorus release risk evaluation and targeted watershed management.