Phosphorus fractions of floodplain sediments and phosphorus exchange on the sediment–water interface in the lower reaches of the Han River in China

Phosphorus fractions and phosphate adsorption characteristics of the floodplain sediments in the lower reaches of the Han River in China were investigated in order to provide the environmental managers with essential data on the Han River ecosystem. The results showed that the total phosphorus (TP) contents ranged from 643.86 to 985 mg kg−1; inorganic phosphorus (IP) was the major fraction of TP, and calcium–bound phosphorus (Ca–P) was the main fraction of IP. Immersion played an important role in bioavailable phosphorus (exch-P and Fe/Al–P) desorption. The phosphorus adsorption process was completed within about 16 h. The desorption amount of phosphorus increased within 7 h and then decreased after 7 h. The contents of native adsorbed phosphorus (wNAPwNAP), zero equilibrium phosphorus concentration (cEPC), total maximal adsorption amount of phosphorus (TQmax) and partitioning coefficient value (Kp) were calculated by corresponding formulae. wNAPwNAP ranged from 5.96 to 8.48 mg kg−1 and cEPC ranged from 0.15 to 0.24 mg L−1. wNAPwNAP was positively related to the exch-P and Ca–P contents (wexch-pwexch-p and wCa–PwCa–P) and negatively related to the Fe/Al–P contents (wFe/Al–PwFe/Al–P). A more significant linear relationship between TQmax and Kp was observed. The floodplain sediments would release phosphorus into the overlying water. The Han River ecosystem should be restored in response to the development of the sustainable Han River ecosystem.