Effect of sediment burial depth on the control of sedimentary phosphorus release by iron/aluminum co-modified calcite and strategy for overcoming the negative effect of sediment burial

After placing an active capping material on surface sediments, the capping layer will be buried by the newly formed sediment. In this research, the influence of sediment burial depth on the performance of iron/aluminum co-modified calcite (FeAlCAL) to suppress sedimentary phosphorus (P) release into overlaying water (OL-water) was studied. Furthermore, in order to find out the strategy for overcoming the negative effect of sediment burial, the efficiencies and mechanisms of three different FeAlCAL treatments (one-time FeAlCAL capping with 3 cm sediment burial, multiple FeAlCAL capping with 1 cm sediment burial, and amendment of top 3 cm sediment with FeAlCAL) in the inhibition of sediment P release were contrastively studied. The results showed that with the increase of sediment burial depth, the efficiency of FeAlCAL to block the release of sediment P into OL-water gradually decreased until the FeAlCAL lost the ability to hinder sediment-P release. In contrast to the one-time FeAlCAL capping in the presence of 3 cm sediment burial, the multiple FeAlCAL capping in the presence of 1 cm sediment burial and amendment of top 3 cm sediment with FeAlCAL both effectively prevented the release of P from sediment into OL-water. All results of this work suggest that although sediment burial can negatively affect the ability of FeAlCAL in the inhibition of sediment P release into OL-water and the negative effect becomes stronger as the sediment burial depth increases, the transformation of the application mode of FeAlCAL from one-time capping to multiple capping or from capping to amendment can overcome the negative influence of sediment burial.