Phosphorus distribution in the sediments of a shallow eutrophic lake, Lake Chaohu, China

In this study, the sediment profiles of total phosphorus (TP), inorganic phosphorus (P-i), organic phosphorus (P-o), C/P and N/P were used to investigate time-dependent P distribution changes in Lake Chaohu. The characteristics of P-i and P-o fractions in the surface sediments were studied and the difference between east and west lake region was also discussed. The P-i and P-o contents displayed a clear gradient from east to west in sediments of Lake Chaohu, and the P-o/P ratios were lower in sediments with industrial and urban pollution sources input in west lake region. The study indicated that different sediments area had diverse concentrations and distributions of P-o fractions due to their different drainage basin and pollution sources. The profile distribution of the C/P and N/P ratios decreased with increasing depths and stayed relatively constant ratios at the depths of 15-30 cm. The C/P and N/P ratios were always below Redfield ratios in sediment profile, indicating P enrichment but likely due to the preferential loss of carbon in respect to phosphorus. The rank order of P-i-fractions extracted was HCl-P-i > NaOH-P-i > NaHCO3-P-i in surface sediments. The relative distribution of NaHCO3-P-i and HCl-P-i was in agreement with the trophic conditions of the regions studied. Among the sequentially extracted P-o forms, the rank order of P-o fractions was residual P-o > HCl-P-o > fulvic acid-P > humic acid-P > NaHCO3-P-o, with mean relative proportion of 5.4:3.4:2.2:1.1:1.0.