Assessment of Methane Variability from Natural Wetlands of Uttar Pradesh, India-Implications for Tropical Countries

Tropical wetlands are one of the most dynamic natural sources of atmospheric methane (CH4) but the CH4 emission data is still scanty to quantify and elaborate the process of CH4 emissions from natural freshwater tropical wetlands. In view of this, the present study attempts to estimate the CH4 emissions from two natural tropical wetlands of Uttar Pradesh, India to further augment the CH4 emission database for tropical countries for improved understanding of CH4 cycling in tropical wetlands. This study elucidates the importance of temporal, site specific and zone-wise dependence of CH4 emission in a wetland. Significantly higher CH4 flux in the summer season than monsoon and winter season at both the locations (p<0.05 for shallow water, deep water and exposed wetland soil zone) clearly define the importance of temperature, water depth, dissolved oxygen, redox potential, biological oxygen demand and plant biomass in regulating the seasonal CH4 flux. Spatial analysis revealed that higher mean annual CH4 flux from the Nawabganj lake (153.5±23.2 mg mG dayG) as compared to the Keetham lake (80.0±11.8 mg mG dayG), is attributed to enhanced anoxic conditions at Nawabganj lake owing to shallow, static and shrinking water base, high plant mediated CH4 flux and boosted autochthonous organic matter production by dense aquatic vegetation present in the lake chiefly including Eleocharis dulcis, Nelumbo nucifera, Ipomoea aquatica. Zone-wise, shallow water zone contributes maximum to CH4 flux than deep water and exposed wetland soil zones at both the sites due to high biological oxygen demand, heavy vegetation infestation and decreased values for water depth, dissolved oxygen and redox potential.