Comparative study of phosphorus adsorption behaviors in lake sediments over short and long periods of time: implication for the prediction of the release of phosphorus by CaCl2 and NaHCO3 extraction.

Ten sediments were collected from the northern part of Taihu Lake, China. They were incubated for 24 h and 80 days to analyze the adsorption characteristics. After adsorption, the residual sediments were extracted with 0.01 M CaCl2 and 0.5 M NaHCO3 separately. Maximum buffer capacities of the Langmuir and Freundlich functions of 80-day incubation were highly correlated with 24 h (R 2 = 0.97). A longer time would enhance the resistance of the sediments to P changes in the water. Adsorption and NaHCO3-P were highly linearly related with R 2 > 0.969, but the relationships between 24 h and 80 days were different. The relationships between adsorption and CaCl2-P could be better explained (97 %) by segmented line models, but the fitting results were affected by incubation time. An interesting finding is that when we plotted the NaHCO3-P and CaCl2-P together by a segmented line model, the data showed a uniform trend unrelated to the incubation time. NaHCO3-P is seldom used to evaluate P status in sediments in comparison with soils. Yet, our results suggested NaHCO3-P is a good bridge to link the sediments P retention ability and P release risk. Due to its simplicity, NaHCO3-P has promising potential in predicting the transfer of P from sediments.