Mobility of different phosphorus pools in the sediment of Lake Dianchi during cyanobacterial blooms

By the method of P fractionation, we examined sedimentary P fractions in Lake Dianchi before and during cyanobacterial blooms, namely in April 2004 and August 2004, respectively. In this study, the whole lake is divided into four areas to discuss P fractions in sediment and the relationship between them and water quality or the nutrient status. The results show that where the water body was much more eutrophic (higher levels of total phosphorus, total nitrogen, chlorophyll and trophic status index) in Lake Dianchi, there can be more potentially available phosphorus (BD-P and NaOH-P) and less no available phosphorus (HCl-P and residual P) in the corresponding sediments. Statistical analysis and statistical plots are used to compare the distribution of every P fraction during cyanobacterial blooms with that before cyanobacterial blooms, and the results indicate that the different P fractions had the different mobility. HCl-P and residual P were relatively stable, while NaOH-P, BD-P and NH4Cl-P were more mobile. BD-P can intensively be released from sediment to water and consequently promote cyanobacterial blooms, and at the same time the NaOH-P concentration increased in sediment, which can result from that BD-P released can be partly immobilized to NaOH-P. During cyanobacterial blooms BD-P can be as a source, but NaOH-P as a sink. Besides, total phosphorus in sediment had no significant differences between two samplings.