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

Abstract

Abstract

Phosphorus (P) is released from sediments primarily through the reduction of iron (Fe³⁺) oxides under anoxic conditions, which dissolves Fe-bound phosphorus and increases dissolved P in lake water. This study aimed to quantify the major sedimentary phosphorus fractions and evaluate 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), redox-sensitive 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 the dominant fractions in both lakes. Principal component analysis (PCA) was performed to examine the relationship between P fractions and sediment characteristics. Pollution levels were assessed using the Single Pollution Index (SPI), with values of 2.07 μg/g for Krishnampathy and 2.14 μg/g for Singanallur, indicating serious pollution in both lakes. Surface water phosphorus concentrations were comparatively lower, while the distribution of HCl-P and Fe-P was influenced by environmental and geochemical factors. The findings indicate that both lakes are at risk of eutrophication. Identifying sedimentary P sources and assessing ecological risks are essential for effective restoration and management of these polluted water bodies.