Transformation of internal sedimentary phosphorus fractions by point injection of CaO2

The transformation of sedimentary phosphorus (P) fractions by point injection of CaO 2 was investigated in this study. The results showed that the addition of CaO 2 increased the dissolved oxygen (DO) in the overlying water as well as its pH. Simultaneously, the concentrations of total organic carbon (TOC), ammonia nitrogen (NH 4 + -N), total phosphorus (TP) and dissolved inorganic P (DIP) in the overlying water were sharply reduced by the point injection of CaO 2 , indicating that this accelerated the mineralisation rate of organic matter. It also favoured the formation and maintenance of the micro-oxidation environment in the deep sediments. NH 4 Cl-P, Fe/Al-P and Ca-P increased significantly, while the Res-P decreased sharply, especially close to the injection point of CaO 2 , accelerating the transformation of P. These results can all be attributed to the oxidation of organic P and the adsorption of dissolved P from the overlying water. Additionally, the NaHCO 3 -extractable phosphorus (Olsen-P) and algal available phosphorus (AAP) were reduced, and their percentages in Ca-P and Fe/Al-P also decreased, especially close to the injection point of CaO 2 . The bioavailable P decreased from 25.6% (the initial) to 17.2% (the mean for the different distances) after the point injection of CaO 2 , when the sum of the Olsen-P and AAP was used to calculate the bioavailable P. This indicates that point injection of CaO 2 favours not only the transformation of P species but also inhibition of the bioavailable P. This is attributable to acceleration of the transformation from bioavailable to inert P.