Does zinc in livestock wastewater reduce nitrous oxide (N2O) emissions from mangrove soils?

- We study the effect of Zn on N2O emissions from mangrove soil-wastewater microcosms.
- Enhancement of N2O emission by wastewater is immediately nullified by high Zn levels.
- Inhibitory effect of Zn disappears gradually and N2O emission recovers in short time.
- Nitrification is the principal mechanism driving atmospheric N2O.
- Nitrification could be enhanced by an appropriate supplement of Zn.

Zinc (Zn) affects nitrogen cycling but the effect of Zn in wastewater on the emission of nitrous oxide (N2O) from the soil has not been reported. This study compared N2O emissions from mangrove soil receiving livestock wastewater containing various Zn2+ concentrations and evaluated how long the effects of Zn would last in these soil-wastewater microcosms. Significant increases in N2O flux were observed soon after the discharge of wastewater with a low Zn content. On the other hand, the flux was reduced significantly in the wastewater with high Zn levels but such inhibitory effect was not observed after tidal flushing. Continuous monitoring of the N2O fluxes also confirmed that the inhibitory effect of Zn was confined within a few hours and the fluxes recovered in 6-9 h after the wastewater was completely drained away. These results indicated that the inhibitory effect of Zn on N2O fluxes occurred immediately after wastewater discharge and disappeared gradually. In the surface soil, nitrate levels increased with the addition of wastewater but there was no significant accumulation of NH4+−N, irrespective of the Zn content in the wastewater. The study also showed that nitrification potential and immediate N2O emissions were inhibited by high Zn levels in the soil, but the total oxidation of ammonium to nitrate was not affected.

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