Characteristics of phosphorus species from typical pollution sources in urban rivers and its response mechanisms with dissolved organic matter

Abstract

Phosphorus (P) significantly influences watershed eutrophication, largely depending on its speciation and composition. In urban rivers, phosphorus pollution has become a critical and challenging issue for water environment management. However, most studies on urban pollution have predominantly focused on total phosphorus (TP), with relatively limited research on phosphorus species. To align with the increasingly stringent environmental standards, there is a pressing need for refined management of phosphorus pollution. Characterizing pollution sources is a prerequisite for the prevention and control of phosphorus pollution in urban rivers. This study had examined sediment samples from a river in Chengdu, a megacity in Southwest China, impacted by typical pollution sources, to investigate the speciation of phosphorus and the compositional characteristics of dissolved organic matter (DOM). A detailed analysis elucidates the response mechanisms between phosphorus speciation and DOM characteristics. This research reveals significant differences in phosphorus speciation among sediments from various pollution sources in urban rivers. During sewage transport from point sources to receiving water bodies, the proportion of labile organic phosphorus (LPo) decreases, while the proportion of non-labile organic phosphorus (NLPo) increases. Among the inorganic P species associated with typical river pollution sources, exchangeable inorganic phosphorus (Ex-Pi) accounts for up to 80%, and iron-bound inorganic phosphorus (Fe-Pi) accounts for as much as 97%. Analysis of DOM characteristics indicates that the sedimentary DOM is predominantly of biogenic origin with low humification. Redundancy analysis reveals the response mechanisms between phosphorus speciation and DOM. Different types of DOM release nutrients through photodegradation and biodegradation, thereby influencing the phosphorus speciation in sediments subjected to various pollution sources. This study had clarified the impact of DOM from different pollution sources on phosphorus speciation, providing a qualitative linkage that had distinguished the contributions of point and non-point source pollution to phosphorus speciation. Offering technical guidance for the prevention and control of eutrophication in urban rivers.