Characteristics of suspended particulate matter in a typical slow-moving river of northern China: Insight into its structure and motion behavior.

To investigate the characteristics of suspended particulate matter (SPM) in rivers of northern China, SPM was collected from 20 sampling sites within the severely polluted slow-moving Ziya River Mainstream (ZRM) and from 20 sampling sites within the less-polluted fast-moving Luanhe River (LR) between October and November of 2016. Physical and chemical attributes of river water from the ZRM and LR were measured; the microstructure, specific surface area and particle size of the SPM were also determined. The SPM had thicker organic coated layers on inorganic particles within the ZRM, compared with the LR, indicating strong interaction of the SPM with the water column. Along the ZRM length, these organic coated layers evolved, first plugging particle pores and then increasing in volume, causing the specific surface area to decrease at first and then increase. The presence of organic coated layers on inorganic particles greatly changed their particle size, density and inducing changes in their motion behavior. Such changes in SPM microstructure were most apparent in the slow-moving polluted ZRM. Given that SPM can adsorb contaminants, such as phosphorus and heavy metals, onto its surfaces and transport them downstream, these changes could have a profound impact on both sediment transport and river ecosystem function. Our results suggest we need to reevaluate our previous river management measures for slow-moving polluted rivers.