Sediment Phosphorus Storage and Release After Aquaculture Cessation: A Case Study of Datong Lake

Reducing external phosphorus (P) inputs is central to eutrophication control, but sediment P release can sustain internal loading and delay lake recovery. This study assessed sediment P composition, vertical distribution, and short-term release potential in Datong Lake, a shallow lake formerly affected by intensive aquaculture. Total phosphorus (TP), dissolved total phosphorus (DTP), and particulate phosphorus (PP) were measured in surface and overlying waters during the dry and wet seasons. Surface-sediment P fractions were characterized in both seasons, whereas dry-season sediments were used for adsorption and release tests, vertical profiling, and depth-specific incubations. Wet-season samples had higher TP, DTP, and PP concentrations in surface water and higher TP and PP concentrations in overlying water. Surface-sediment P was predominantly inorganic, with Ca-P as the largest inorganic fraction; bioavailable P accounted for about 32% of TP. In the 24-h batch tests, the adsorbed P amount exceeded the released amount. Total P and its NaOH-extractable and organic fractions were enriched in the upper sediment. Across the 1–5 to 21–25 cm intervals, 15-d cumulative P release decreased from 22.9 ± 1.9 to 7.2 ± 1.0 mg·kg−1, and the initial 3-d release rate decreased from 1.13 ± 0.18 to 0.24 ± 0.07 mg·kg−1·d−1. Overall, Datong Lake sediments contained high P concentrations but exhibited limited short-term release, with the greatest release amount and rate occurring in the upper sediment.