Cross-continental importance of CH 4 emissions from dry inland-waters.

Despite substantial advances in quantifying greenhouse gas (GHG) emissions from dry inland waters, existing estimates mainly consist of carbon dioxide (CO ₂ ) emissions. However, methane (CH ₄ ) may also be relevant due to its higher Global Warming Potential (GWP). We report CH ₄ emissions from dry inland water sediments to i) provide a cross-continental estimate of such emissions for different types of aquatic systems (i.e., lakes, ponds, reservoirs, and streams) and climate zones (i.e., tropical, continental, and temperate); and ii) determine the environmental factors that control these emissions. CH ₄ emissions from dry inland waters were consistently higher than emissions observed in adjacent uphill soils, across climate zones and in all aquatic systems except for streams. However, the CH ₄ contribution (normalized to CO ₂ equivalents; CO ₂ -eq) to the total GHG emissions of dry inland waters was similar for all types of aquatic systems and varied from 10 to 21%. Although we discuss multiple controlling factors, dry inland water CH ₄ emissions were most strongly related to sediment organic matter content and moisture. Summing CO ₂ and CH ₄ emissions revealed a cross-continental average emission of 9.6 ± 17.4 g CO ₂ -eq m ^-2  d ^-1 from dry inland waters. We argue that increasing droughts likely expand the worldwide surface area of atmosphere-exposed aquatic sediments, thereby increasing global dry inland water CH ₄ emissions. Hence, CH ₄ cannot be ignored if we want to fully understand the carbon (C) cycle of dry sediments.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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