Effects of water richness and seasonality on atmospheric methane emission from the wetlands of deltaic environment

Abstract

Estimation and mapping of wetland methane (CH4) emission is carried out from the wetlands of mature Ganges deltaic environment of India. Wetlands are firstly demarcated into six types and CH4 emission is estimated for each wetland types during pre and post-monsoon seasons in order to assess seasonality effects on methanogenesis across wetland habitat types. Water Richness (WR) of the wetlands area was also assessed using Machine Learning (ML) algorithms to investigate its effect on CH4 emission. Results show significant variation of wetland CH4 emission influenced by WR and seasonality. Very high WR zone is found over almost 18% wetland area where average monthly emission is <0.5 ton/km2. This rate is much lower than the average monthly emission of very low WR zone (>3.0 ton/km2) covering more than 35% of the wetland area. Average monthly emission during pre-monsoon season is about 0.18 ton/km2 and which decreases to 0.15 ton/km2 during post-monsoon season. Considerable seasonal wetland areas make greater total CH4 emission during post-monsoon month than pre-monsoon. Highest average monthly emission rate is found over lakes which is 1.73 ton/km2 during pre-monsoon and reduces to 0.54 ton/km2 during post-monsoon followed by marshy wetlands. The bheries (local name of embanked wetland diurnally controlled by tidal water mainly used for pisciculture) show the lowest emission rate which is not more than 0.08 ton/km2.