Distribution of Inorganic Phosphorus Fractions in Sediments of the South Han River over a Rainy Season

Abstract

Rain events are extremely important for phosphorus (P) dynamics in rivers since large portions of annual river P loads can be transported in particulate forms during only a few major events. Despite their importance, a precise estimation of P contribution in river sediments after rainy seasons has rarely been reported. This study estimated the longitudinal variation in the concentrations of different inorganic P fractions in bed sediments of the South Han River over a rainy season, through using the sequential extraction method. Non-apatite P was the dominant form, representing more than 60% of total inorganic P (TIP) content in sediments. Although no significant variation of TIP contents was observed, the proportion of bioavailable P in TIP pools decreased after the rainy season. The concentrations of individual inorganic P fractions (NH₄Cl-P, NH₄F-P, NaOH-P, and H₂SO₄-P) were significantly different across sites and after the rainy season (p < 0.05, two-way ANOVA). NH₄F-P and NaOH-P concentrations in sediments increased in a downstream direction. After the rainy season, NH₄Cl-P concentrations in sediments decreased whereas NH₄F-P and H₂SO₄-P concentrations increased. The redistribution of individual P fractions in sediments observed after rainy seasons were possibly due to the changing contribution of various sources of runoff and the variation in flow related particle size. Current estimation of P in bed sediments of the South Han River suggests a lower potential of internal P loading from sediments after the rainy season.