High mobilization of phosphorus in black-odor river sediments with the increase of temperature

Highlights: • Pore water phosphorus (P) concentration increased with rising temperatures in black-odor river. • Reduction of Fe (III) oxyhydroxides was one of the major reasons for the release of P in sediments. • Competing absorption of minerals by DOM was another reason for the release of P in sediments. Increased temperatures affect water quality and ecology. However, the response of geochemical cycles of phosphorus (P) in black-odor river sediments to increased temperatures is still unclear. In this study, we found that pore water soluble reactive phosphorus (SRP) concentrations in sediments significantly increased with the rising of temperature, by 28% and 87% at 25 °C and 35 °C, respectively, compared with concentration at 15 °C (p < 0.01, independent samples t-test). The significant decrease of iron (Fe) binding P in sediments was observed (p < 0.01) because of dissolved oxygen (DO) and redox potential (Eh) decreasing with the rising of temperature from 15 °C to 35 °C. This demonstrated that the reduction of Fe (III) oxyhydroxides was one of the major reasons for the release of SRP in sediments. Furthermore, the mobility of P increasing through competing absorption of minerals by dissolved organic matter (DOM) was another reason for the release of SRP in sediments. This was supported by the significant decrease of immobile-P, and increase of mobile-P in sediments. Additionally, the simultaneous increase of SRP and DOM, and a significant positive correlation between them were observed in sediments with increasing temperatures (r ≥ 0.776, p < 0.001).