The Importance of Inland Water CO₂, CH₄, and N₂O for Summertime Greenhouse Gas Exchange With the Atmosphere in Arctic Tundra Lowlands

Inland waters in Arctic landscapes act as conduits of terrestrial organic material, transporting and processing organic material into the greenhouse gases (GHGs) carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), and subsequently exchanging these gases with the atmosphere. To assess the role of inland water emissions in the Arctic GHG budget, it is necessary to quantify their emissions in relation to the terrestrial sink capacity. We present measurements of dissolved CO₂, CH₄, and N₂O from lake, pond, and low-order fluvial systems across two summers (2016–2017) in the Arctic Siberian Indigirka River tundra lowlands. During May–July 2017, the region experienced large-scale flooding, of which we captured the tail end. Using remote sensing images to upscale inland water emissions to an area of approximately 18 km², we calculated combined carbon (C) emissions, CO₂-C, and diffusive CH₄-C under nonflood and flooded scenarios. These ranged from 7.03 ± 1.30 Mg C d⁻¹ (nonflood; mean ± SD) to 9.63 ± 1.24 Mg C d⁻¹ (flooded). Integrating these values into the total C landscape exchange offset the terrestrial C sink by ∼9–∼13%. When N₂O emissions were calculated as CO₂ equivalents, these emissions were negligible relative to CO₂ and CH₄. Our study shows that in the northeast Siberian Arctic tundra, summertime CO₂ and CH₄ emissions from inland waters are a potentially important component of landscape C exchange with the atmosphere, offsetting the terrestrial sink capacity, and this may be an important consideration for constraining future Arctic responses to climate warming.