Chemical speciation, source apportionment, and pollution assessment of phosphorus in sediments from typical urban...

Urban lakes play a vital role in flood disaster mitigation and water-climate maintenance. However, excessive phosphorus inputs resulting from urban development constitute a significant factor in the deterioration of ecosystems. In this study, samples of sediment profiles from three representative urban lakes (Xianghu Lake, Qianhu Lake, and Aixihu Lake) in Nanchang were collected to investigate the sources and the pollution condition of phosphorus. Results indicated that sediments in Qianhu Lake exhibited the highest concentration of total phosphorus (923.06-1630.17 mg/kg), while Xianghu Lake exhibited the lowest levels. Calcium-bound phosphorus (Ca-P) dominated in all three lakes (accounting for over 30% of total phosphorus), followed by iron-bound phosphorus (Fe-P) and detrital phosphorus (De-P). While the organic phosphorus (Org-P) and exchangeable phosphorus (Ex-P) constituted the lowest proportions. In all the lakes, clay dominated the sediment composition (≥ 34%), followed by coarse silt, while fine silt was the least abundant. Correlation analysis revealed that grain size and organic matter constrained the concentrations of phosphorus speciation. The Absolute Principal Component Score-Multiple Linear Regression model (APCS-MLR) revealed that phosphorus pollution in Xianghu Lake, Qianhu Lake, and Aixihu Lake was predominantly driven by agricultural non-point sources, with the contributions of more than 35%, followed by industrial emissions and domestic sewage, which corresponded with the extensive agricultural land around the lake. Nemerow integrated pollution index analysis revealed that all the lakes were heavily polluted, with the F values of the three lakes more than 1.90. Consequently, comprehensive management measures, including optimizing agricultural fertilization-irrigation forms and restricting pollutant discharges, are required to prevent further deterioration. This study is of practical significance for the prevention of lake eutrophication. It provides a scientific basis for biogeochemical cycles and the protection and management of aquatic ecosystems in the urban lakes.