Nitrate-dependent anaerobic methane oxidation (N-DAMO) as a bioremediation strategy for waters affected by agricultural runoff

Agricultural drainage ditches are subjected to high anthropogenic nitrogen input, leading to eutrophication and greenhouse gas emissions. Nitrate-dependent anaerobic methane oxidation (N-DAMO) could be a promising remediation strategy to remove methane (CH4) and nitrate (NO3-) simultaneously. Therefore, we aimed to evaluate the potential of N-DAMO to remove excess NO3- and decrease CH4 release from agricultural drainage ditches. Microcosm experiments were conducted using sediment and surface water collected from three different sites: a sandy-clay ditch (SCD), a freshwater-fed peatland ditch (FPD), and a brackish peatland ditch (BPD). The microcosms were inoculated with an N-DAMO enrichment culture dominated by Candidatus Methanoperedens and Candidatus Methylomirabilis and supplemented with (CH4)-C-13 and (NO3-)-N-15. A significant decrease in CH4 and NO3- concentration was only observed in the BPD sediment. In freshwater sediments (FPD and SCD), the effect of N-DAMO inoculation on CH4 and NO3- removal was negligible, likely because N-DAMO microorganisms were outcompeted by heterotrophic denitrifiers consuming NO3- much faster. Overall, our results suggest that bioaugmentation with N-DAMO might be a potential strategy for decreasing NO3- concentrations and CH4 emission in brackish ecosystems with increasing agricultural activities where the native microbial community is incapable of efficient denitrification. Nitrate-dependent anaerobic methane oxidation might be an efficient bioremediation strategy to decrease nitrate concentration and methane emission from brackish drainage ditches.

Automated summary

Agricultural drainage ditches with high nitrate input contribute to eutrophication and greenhouse gas emissions. Nitrate-dependent anaerobic methane oxidation (N-DAMO) could be an effective strategy to simultaneously remove methane (CH4) and nitrate (NO3-). Microcosm experiments were conducted using sediment and water samples from different ditches, and the results showed that N-DAMO effectively reduced CH4 and NO3- concentrations in brackish peatland ditch sediment. However, in freshwater sediments, N-DAMO was outcompeted by heterotrophic denitrifiers, resulting in negligible effects on CH4 and NO3- removal. Overall, our study suggests that N-DAMO bioaugmentation may be a potential approach to decrease NO3- concentrations and CH4 emission in brackish ecosystems where native microbial communities are not efficient in denitrification.