Estimation of Greenhouse Gas Emissions from Ganga River Sediment, India

Greenhouse gas production in riverine sediments is extensively influenced by the aerobic and anaerobic breakdown of organic matter and the processes of nitrification and denitrification. These processes are further enhanced by nitrogen-rich organic substrates in the sediments, which produce potent GHGs such as Methane (CH₄) and Nitrous Oxide (N₂O). While extensive research has been conducted on terrestrial ecosystems, little attention is given to estimating GHG emissions from riverine sediments. In this context, an incubation study was conducted to estimate the emissions of CH₄ and N₂O from sediment samples collected from the Ganga River at three locations representing varied environmental conditions: the urban area, city outskirts, and an agricultural area. Samples were taken during the winter (wet season) and summer (dry season) to assess seasonal emission variations. The study observed a wide range in the daily production of CH₄, varying from 0.51 μg g^-1d^-1 to 3.82 μg g^-1d^-1 across the sampling sites (S1, S2, and S3). The highest CH₄ production was observed during the summer (March) season at the urban periphery (S1), indicating that warmer temperatures and increasing microbial activities during the dry season may enhance CH₄ emissions. Similarly, the daily N₂O production ranged from 1721.37 μg g^-1d^-1 to 2024.57 μg g^-1d^-1, with the highest N₂O emissions occurring at S3 during the summer season. N₂O production is driven primarily by the microbial reduction of nitrates in anoxic conditions, and higher nitrogen inputs from fertilizers at the agricultural site likely amplify denitrification, leading to elevated N₂O emissions. Moreover, the significant positive correlation of CH₄ production with Total Organic Carbon (TOC), C/N ratio and Electrical Conductivity (EC), while N₂O with EC, pH, and Water Temperature (T_W) confirms the crucial role of environmental variables in GHG emissions. These findings highlighted the substantial role of riverine sediments as sources of GHG emissions, which are often understated in national/global GHG inventories. Riverine sediments, particularly in regions influenced by human activities, are significant in the global carbon budget. The study emphasizes incorporating riverine sediments in future GHG emission models and inventories, especially in the context of climate change mitigation strategies. In addition, more comprehensive studies are required to understand the GHG dynamic in these environments and their impact on global climate change.