Complex responses of suspended particulate matter in eutrophic river and its indicative function in river recovery process

Abstract Water environment and hydrodynamic condition of a river exerts a powerful influence on Suspended Particulate Matter (SPM) in rivers. Complex responses of SPM in rivers under changing water quality and hydrodynamic condition remain unclear and its indicative role in river recovery process is neglected. In this paper, twenty SPM samples were collected in June 2017 (rainy season) in Ziya River Mainstream (ZRM). The eutrophication levels of ZRM, sedimentation property and P fractions of SPM, and P-buffering intensity of the ZRM were investigated and compared with our previous research in arid season. The results showed eutrophication level was lower in rainy season than in arid season with mean Eutrophication Index (EI) values of 90.02 (seriously eutrophied) and 103.48 (extremely eutrophied), respectively. SPM in arid season has higher Loss On Ignition (LOI) content and was easier to remain suspension. The total amount of NaOH extracted Phosphorus (NaOH-P) and Organic Phosphorus (OP) fractions in SPM and Phosphorus (P) buffering intensity of ZRM were higher in arid season than in rainy season. Differences in water quality of a river can induce complex responses of SPM in its microstructure, P buffering ability and can act as a positive yet negative role in river eutrophication control. We put forward a P based river recovery process and suggest two-step river restoration measures, we point out rainy season is the reasonable timing to conduct measures in decreasing SPM concentration under the premise of mitigating P input. These results deepen our understanding on the role of SPM in P cycling in fluvial system and provide a new idea for river restoration work worldwide.