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 > NaHCO 3 -P i in surface sediments. The relative distribution of NaHCO 3 -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 > NaHCO 3 -P o , with mean relative proportion of 5.4:3.4:2.2:1.1:1.0.