Geochemical Fractionation and Internal Loading of Phosphorus in Urban Lake Sediments in Coimbatore, Tamil Nadu, India

Phosphorus (P) is primarily released from sediments through the reduction of iron (Fe³⁺) oxides under anoxic conditions, leading to the dissolution of Fe-bound phosphorus and an increase in dissolved phosphorus in lake water. This study aimed to quantify the major sedimentary phosphorus fractions and assess their ecological risks in Krishnampathy and Singanallur lakes in urban Coimbatore during the post-monsoon season. The sequential extraction method was used to analyze loosely sorbed exchangeable P (NH₄Cl-P), redoxsensitive P (Fe-P), metal oxide-bound P (NaOH-P), calcium-bound P (HCl-P), residual P (Res-P), and total phosphorus (TP). Fe-P and NaOH-P were identified as the dominant fractions in both lakes. Principal component analysis (PCA) was employed to explore the relationship between P fractions and sediment characteristics. Pollution levels, determined using the Single Pollution Index (SPI), were 2.07 for Krishnampathy and 2.14 for Singanallur, indicating serious pollution in both lakes. Surface water phosphorus concentrations were relatively lower, while the distribution of HCl-P and Fe-P was influenced by environmental and geochemical factors. The results suggest that both lakes are at risk of eutrophication. Identifying sedimentary P sources and evaluating ecological risks are crucial for effective restoration and management of these polluted water bodies.