EFFECTS OF AIR-DRYING ON PHOSPHORUS SORPTION IN SHALLOW LAKE SEDIMENT, CHINA

Air-drying has significant influences on phosphorus sorption behaviors in soils. It is urgently necessary to expend the relevant knowledge to sediments of lakes, especially large eutrophic ones. Sediments were collected at different sites in a Chinese large shallow eutrophic lake (Lake Chaohu) and an urban shallow lake (Lake Donghu) in November 2007; contents of organic matter (OM) were measured. Phosphorus sorption behavior fitted Langmuir equation well. Compared to the field-moist sample, the air-dried sediments had significantly lower sorption energy (K). Additionally, there was a significant positive relationship between the OM content and K value in the field-moist sediments. The changes in geochemical characteristics of iron oxide and organic carbon may be mainly responsible for the decreasing K value in air-dried sediment. Furthermore, in the incubation experiments, the air-dried sediments generally gave higher concentrations of soluble reactive phosphorus coupled with alkaline phosphatase activity, which was mainly due to the decreased phosphorus sorption energy, because there was no significant differences of pH values and dissolved oxygen concentrations between the air-dried and field-moist sediments. Finally, in contrast with the field-moist samples, the air-dried ones showed a significantly positive relationship between OM content and EPC0 value, suggesting that the breakdown of OM during drying may be a major source of P upon reflooding.Air-drying has significant influences on phosphorus sorption behaviors in soils. It is urgently necessary to expend the relevant knowledge to sediments of lakes, especially large eutrophic ones. Sediments were collected at different sites in a Chinese large shallow eutrophic lake (Lake Chaohu) and an urban shallow lake (Lake Donghu) in November 2007; contents of organic matter (OM) were measured. Phosphorus sorption behavior fitted Langmuir equation well. Compared to the field-moist sample, the air-dried sediments had significantly lower sorption energy (K). Additionally, there was a significant positive relationship between the OM content and K value in the field-moist sediments. The changes in geochemical characteristics of iron oxide and organic carbon may be mainly responsible for the decreasing K value in air-dried sediment. Furthermore, in the incubation experiments, the air-dried sediments generally gave higher concentrations of soluble reactive phosphorus coupled with alkaline phosphatase activity, which was mainly due to the decreased phosphorus sorption energy, because there was no significant differences of pH values and dissolved oxygen concentrations between the air-dried and field-moist sediments. Finally, in contrast with the field-moist samples, the air-dried ones showed a significantly positive relationship between OM content and EPC0 value, suggesting that the breakdown of OM during drying may be a major source of P upon reflooding