Ebullition mediated transport dominates methane emission from open water area of the floating national park in Indo Burma hotspot.

Abstract

Ebullition is an important route of methane emission from aquatic ecosystems. Ebullitive CH₄ emissions from the wetlands, particularly the mountain wetlands of Eastern Himalayan, are poorly understood. To gain insights into the role of ebullition in CH₄ emissions and understand the factors influencing CH₄ ebullition, we conducted field measurements of the spatial and temporal variation of ebullition in a freshwater wetland area in floating national park (40 sq. km, 780 m amsl, maximum depth < 4.5) in Northeast India. The average ebullitive CH₄ flux ranged from 220.24 to 1889.35 mg m^-2 d^-1, while the overall CH₄ fluxes varied widely ranging from 345.81 to 2240.56 mg m^-2 d^-1. Methane constituted 90.18% of the gas bubbles produced from the sediment, with CO₂ comprising 8.82% of the total sediment gas in the wetland. This suggests that CH₄ emission through ebullition plays an important role in transporting biogenic CH₄ to the atmosphere. The ebullition rate was markedly higher during summer and lower during winter and exhibited a significant seasonal variation. At a spatial scale, the sites with dense aquatic vegetation growth increase CH₄ emission where plants derived autochthonous sediment organic matter, substantiating the supply of carbon substrate for CH₄ production. Linear mixed-effect models revealed that water temperature, organic matter, organic carbon and dissolved organic matter are the important factors affecting the ebullitive methane flux. Our results indicate that mountainous wetlands with organic-rich sediments may be potential hotspots for CH₄ ebullition. However, the lack of information on these wetlands in the scientific literature emphasizes the need for further research.