The effect of anthropogenic activities on the phosphorus-buffering intensity of the two contrasting rivers in northern China.

The phosphorus (P)-buffering ability of suspended particulate matter (SPM) from the Ziya River Mainstream (ZRM) and the Luanhe River (LR) of northern China was investigated in this study. Forty samples of SPM from the ZRM and LR were collected in October and November of 2016. The ZRM has slow flow and poor water quality, while the LR has fast flow and reasonably good water quality. Under a scanning electron microscope, the SPM from the ZRM had a more complex microstructure than that from the LR, perhaps because of the slower flow and heavier pollution in the ZRM. P fractions in both SPM and water samples were determined using standard measurement and testing program methods. The equilibrium P concentration was used to determine the influence of SPM on soluble reactive P (SRP) concentrations. These SRP fractions were used to evaluate the P-buffering intensity of the two rivers. Differences in SPM microstructure resulted in the SPM from ZRM having a stronger P-buffering ability than the LR, making SPM an effective vector for SRP. Anthropogenic activities likely contributed to the differences in both microstructures of the SPM and P-buffering intensity of the rivers. A conceptual model was developed to show how anthropogenic activities influence the P-buffering intensity of the two rivers. As far as we know, this is the first time that the P-buffering intensity has been compared between two rivers that have been severely impacted by anthropogenic activities. Our findings provide an important reference for similar rivers worldwide.