Organic phosphorus in shallow lake sediments in middle and lower reaches of the Yangtze River area in China

Thirteen sediment core samples (0-10 cm) were taken from the seven lakes in the middle and lower reaches of the Yangtze River to determine the contents and distributions of organic phosphorus (P) fractions in the sediments of the shallow lakes in the area. The organic P fractions in the sediments were in the order of moderately labile organic P (MLOP) > moderately resistant organic P (MROP) > highly resistant organic P (HROP) > labile organic P (LOP), with average proportional ratios of 13.2:2.8:1.3:1.0. LOP, MLOP, and MROP were significantly related to the contents of total organic carbon (TOC), water-soluble P (WSP), algal-available P (AAP), NaHCO3-extractable P (Olsen-P), total P (TP), organic P (OP), and inorganic P (IP). However, HROP was significantly related to OP and weakly correlated with TOC, WSP, AAP, Olsen-P, TP or IP. This suggested that organic P, especially LOP and MLOP in sediments, deserved even greater attention than IP in regards to lake eutrophication. In terms of organic P, sediments were more hazardous than soils in lake eutrophication. Although OP concentrations were higher in moderately polluted sediment than those in heavily polluted sediment, LOP and MLOP were higher in the heavily polluted sediment, which indicated that heavily polluted sediment was more hazardous than moderately polluted sediment in lake eutrophication.