Extensive land subsidence and submergence occurred in the coal mining areas (Huainan and Huaibei) in Anhui Province, China. As a result, lots of subsided lakes have been formed due to their unique geological features. Four typical lakes were selected to evaluate the internal phosphorus (P) releasing risk based on the specification of P, Fe and Al from the sediments. Sediment P, Fe and Al in the top 5 cm were extracted sequentially, aiming at obtained fractionation for environmental indicators. Experiments of P isothermal adsorption were conducted to characterize P sorption ability. The results suggested that P internal loading potential was related to Al and Fe compounds in sedimentary environments of soil inundation, primarily determined by regional soil properties. Internal P releasing risk was mainly controlled by the properties of calcareous soils in the Huaibei; whereas controlled by Fe and Al in the Huainan. Overall, the obtained results fit well with the model proposed by Kopáček et al.(2005), which predicted low P flux as molar ratio of [NH4Cl-Al + BD-Al + NaOH-Al] : [NH4Cl-Fe + BD-Fe] >3 or [NaOH-Al] : [NH4Cl-P + BD-P] >25 from sediments when anoxia is developed. However, this threshold has site-specific flexibility, with its lower limit approaching 20:1 applicable for the three lakes in Huainan. Higher loads of external input organic matters or enriched Fe oxides bound P tend to change this limit and lead to internal loading risk with environmental anoxia.

• Sun, Pengfei(Ph.D Candidate, Department of Environmental Engineering, Hanseo University)
• Yi, Qitao(Associate Professor, School of Earth and Environment, Anhui University of Science and Technology, China.)
• Kim, Youngchul(Professor, Department of Environmental Engineering, Hanseo University) Corresponding Author