Factors influencing spatio-temporal variation of methane and nitrous oxide emission from a tropical mangrove of eastern coast of India

We have studied the seasonal and tidal variation of methane (CH4) and nitrous oxide (N2O) emission from the intertidal sediment of Bhitarkanika mangrove in the east coast of India. Seasonal variability study was conducted at five sites (three replicate of each site) inside the core area of the national park during three different seasons (summer, monsoon and winter) whereas tidal variation was studied at three different sites outside the core area during monsoon and winter season. Both CH4 and N2O emission from the intertidal sediment were significantly higher under the low tide condition during the winter season. During the study period CH4 emission from five different sites was ranged between 0.08 and 2.30 mg m−2 h−1 and the N2O emission was ranged between 9.0 and 187.58 μg m−2 h−1. Average seasonal N2O emission (μg m−2 h−1) from five different sites followed the order: winter (115.60 ± 21.90) > summer (45.29 ± 7.78) > monsoon (16.98 ± 2.54). CH4 and N2O emission was also recorded significantly higher during the winter season over the tidal cycle of three sampling locations. The CH4 emission was negatively correlated with sediment salinity (r = −0.91, P < 0.05) and SO4-2 (r = −0.89, P < 0.05) concentration whereas; the N2O emission was positively correlated with sediment salinity (r = 0.48) and NO3−-N (r = 0.88, P < 0.05) concentration during the monsoon season. Positive correlation of N2O emission with the sediment NO3−-N indicates possible influence of upstream anthropogenic activities on N2O emission from the mangrove sediment. In general, methylamine utilizing methanogen and denitrifying bacterial population was significantly higher during winter season in the mangrove sediment. The study concludes that the CH4 and N2O emission from the sediment at different sites during different seasons are influenced by allochthonous carbon and nitrogenous materials.