Combined use of calcium nitrate addition and anion exchange resin capping to control sedimentary phosphorus release and its nitrate‑nitrogen releasing risk

Abstract

Calcium nitrate (Ca(NO3)2) addition can be used to control the release of phosphorus from sediments, however it can also cause an increase in the concentration of nitrate‑nitrogen (NO3−-N) in the water column. The risk of NO3−-N release from the Ca(NO3)2-injected sediments may be reduced by the placement of the anion exchange resin (AER) capping layer. In this study, the effectiveness of the combined use of Ca(NO3)2 addition and AER capping to prevent the liberation of phosphorus from sediments was investigated, and the reduction of the risk of NO3−-N released from the Ca(NO3)2-injected sediment by the AER capping was also evaluated. The combined application of Ca(NO3)2 addition and AER capping could tremendously reduce the amount of soluble reactive phosphorus (SR-P) in the overlying water, with SR-P reduction rates of 75.9–98.7%. Furthermore, it could cut down the contents of high-resolution diffusive gradients in thin films (DGT)-labile phosphorus in the sediments, resulting in the formation of phosphorus static layer in the upper sediments. The combined treatment using Ca(NO3)2 and AER had a relatively small effect on the contents of mobile phosphorus in the sediments, but it could greatly increase the amount of residual phosphorus in the top 30mm sediments (increased by 27.7–42.9%). The amount of NO3−-N in the overlying water under the action of the combined treatment method using Ca(NO3)2 and AER was much lower than that under the action of the single Ca(NO3)2 treatment during the early stage of sediment remediation. In conclusion, the combined use of Ca(NO3)2 addition and AER capping is a more promising strategy for the control of sedimentary phosphorus release than the single use of Ca(NO3)2 addition from the point of view of both the control efficiency of P release from sediments and the releasing risk of the added nitrate.