Soil greenhouse gas fluxes in tropical mangrove forests and in land uses on deforested mangrove lands

- Emissions of CO2 and CH4 are higher by 2.6 and 6.6 times in mangrove forest than their replacement non-forest land uses.
- N2O emission is higher by 34 times in non-forest land uses than mangroves.
- Mapping spatial variation of soil GHG fluxes had 75% to 83% accuracy.
- Non-forest land uses cannot offset their emissions on-site due to lack of woody vegetation.

Mangrove forests are important carbon sinks in the tropics, yet tropical mangrove deforestation and land use conversion still persists. Reporting of greenhouse gas (GHG) emissions from natural and anthropogenic sources in wetlands are important in regional and national emissions inventories. However, very few studies have been conducted to measure on the GHG fluxes in coastal wetlands, particularly in mangrove forest and non-forest land uses in deforested mangroves. We investigated the soil fluxes of CO2, CH4 and N2O in mangrove forest and non-forest land uses on deforested mangrove areas (i.e. abandoned aquaculture ponds, coconut plantations, abandoned salt ponds, and cleared mangroves) in the coasts of Honda Bay, Philippines. Results showed that the emissions of CO2 and CH4 were higher by 2.6 and 6.6 times in mangrove forests (110 and 0.6 kg CO2e ha − 1 day − 1, respectively) while N2O emissions were lower by 34 times compared to the average of non-forest land uses (1.3 kg CO2e ha − 1 day − 1). CH4 and N2O emissions accounted for 0.59% and 0.04% of the total emissions in mangrove forest as compared to 0.23% and 3.07% for non-forest land uses, respectively. Site-scale soil GHG flux distribution could be mapped with 75% to 83% accuracy using Ordinary Kriging. Unlike mangroves that can offset all GHG emissions through CO2 uptake from photosynthesis, the non-forest land uses cannot offset their emissions on-site as they are usually devoid of vegetation. Our results could be utilised in higher tier national GHG inventories, to refine regional and global estimates of GHG emissions in mangrove wetlands, and improve policy on coastal wetlands conservation.