Comparative accounting of methane and nitrous oxide fluxes with related soil parameters of degraded mangrove wetlands and adjacent rice fields in Sundarban, India

Abstract

In Sundarban, around 10.5% of mangroves are primarily converted to rice-based system by anthropogenic activities during last 80 years. Both mangrove wetlands and rice fields, typically providing a passage for transporting the greenhouse gases (methane and nitrous oxide) from soil systems to atmosphere. In this article, we attempted to quantify the seasonal methane (CH4) and nitrous oxide (N2O) fluxes from six different degraded mangroves and adjacent rice fields to know how the land use change affects the fluxes. In mangroves, the average CH4 fluxes were higher in monsoon compared to pre-monsoon, winter, and summer season. Methane emissions were also higher in monsoon and summer in rice than winter and pre-monsoon. Overall, the mean CH4 fluxes were more in rice (2665 μg m−2 h−1) than mangrove (159 μg m−2 h−1). However, the average N2O fluxes were higher in summer followed by monsoon in mangroves, while, in rice, it was higher in monsoon. Like CH4 the higher mean N2O flux was observed in rice (72 μg m−2 h−1) over mangrove (69 μg m−2 h−1). The soil labile carbon pools were higher in mangroves than rice, but the enzymatic activities were more in rice. The fluxes were positively correlated with the soil enzymatic activities, whereas those were negatively correlated with soil pH, EC, and salinity. So, we found shifting of mangrove to rice resulting in higher CH4 and N2O fluxes from surface soils. Therefore, regeneration and protection of mangroves should be given priority in upper Sundarban where anthropogenic activities are prevailed to mitigate climate change.