Effect of autotrophic denitrification on nitrate migration in sulfide-rich marine sediments

Abstract

This study aims to investigate how NO3 − reduction affects the migration of NO3 − in marine sediments and evaluate whether the overlying seawater would be contaminated by NO3 − injection for in situ bioremediation. The migration of NO3 − in sandy silt sediment with high acid volatile sulfide (AVS) content and in clayey silt sediment with relatively low AVS content was investigated through column experiments with 5 weeks of incubation. Results showed that NO3 − reduction through autotrophic denitrification contributed to 93.1 and 48.9 % of total NO3 − reduction in sandy silt and clayey silt sediments, respectively. In sandy silt sediment with high AVS content, NO3 − tended to migrate upwards through gas cavities formed during the movement of N2 gas produced by NO3 − reduction. Meanwhile, greater NO3 − consumption by AVS oxidation can effectively prevent the NO3 − release into seawater. In clayey silt sediment with relatively low AVS content, few gas cavities produced due to insignificant NO3 − reduction and high density of NO3 − solution made the downward NO3 − migration more significant. Without great NO3 − consumption, NO3 − from clayey silt sediment was found to be present in the seawater after 5 weeks of incubation. Autotrophic denitrification has a significant impact on NO3 − reduction in marine sediments. The reduction of NO3 − resulting from autotrophic denitrification can influence its preferential migration path in marine sediment and the possibility of its release into seawater.