Variations in the sediment phosphorus fractions and their release according to precipitation in the Han River, South Korea

Purpose: In this study, we investigated the temporal and spatial variations of the inorganic phosphorus (P) fractions and their release using sediment collected from three weirs built along the Han River in South Korea. Methods: Sediment and water samples that were collected upstream of Gangcheon, Yeoju, Ipo weir in rainy and non-rainy seasons were incubated during 0, 3, and 7 days. The inorganic P fraction concentrations of the sediment sample were analyzed after incubation. Results: The sum of the four inorganic P fractions was significantly higher in the non-rainy season than in the rainy season. The P fractions with the highest concentrations, reductant soluble P- and Ca-bounded P, were also higher in the non-rainy season than in the rainy season. From the incubation experiment, it was observed that the concentration of inorganic P in the sediments tends to decrease with the incubation time in the non-rainy season resulting in the significant correlation between changes in Al- and Fe-bounded P in the sediment and PO₄-P concentration in the overlying water layer. Sediments of three weirs were dominantly affected by non-point sources as indicated by EF (enrichment factor) value using P fractions. The Al-bounded P release rate was positively correlated with the pH, while those of the Fe- and Ca-bonded P were correlated with the organic matter. Conclusion: The fractionation and release of P in the sediments was affected by the rainfall and physiochemical factors. The results of this study will enhance our understanding of the water quality, as well as the effects of impoundment and rainfall on sediment, thereby aiding in an efficient management of the river environment.