Impact of land cover and sediments on GHG emissions from Indonesian rivers

Abstract

The evasion of methane (CH₄) and carbon dioxide (CO₂) from tropical rivers represents a substantial contribution, where land covers and riverbed biogeochemistry significantly apply in situ controls. However, CH₄ and CO₂ emissions from tropical rivers are less constrained. Riverine emissions from Indonesia—the world’s most populous tropical island—are undergoing rapid land cover changes and have not been adequately studied. Here, we investigated the spatial variations of concentration and fluxes of CH₄ and CO₂ from rivers with different land cover types in Yogyakarta. Our result showed an intense CH₄ ebullition rate (94.51 ± 126.09 mmol m⁻² d⁻¹) approximately 47 times higher than the estimated global mean value for streams and rivers. Elevated ebullition rates were controlled by enriched clayey sediments through agricultural activities, which increase organic carbon availability, foster reduced conditions, and support methanogenic archaea. CO₂ diffusion was preponderant in agricultural-dominated rivers. CO₂ emissions were governed by sediment texture, microbial respiration, and lateral CO₂ input from river corridors. These findings highlight the role of the target river in shaping CH₄ and CO₂ dynamics, particularly the impact of agricultural practices and sedimentation. This study not only tackles the scarcity of data on riverine greenhouse gas emissions in Indonesia but also highlights the importance of managing agricultural activities and sedimentary processes to mitigate CH₄ and CO₂ in tropical systems.