Inland Waters Increasingly Produce and Emit Nitrous Oxide

Nitrous oxide (N₂O) is a long-lived greenhouse gas and currently contributes ∼10% to global greenhouse warming. Studies have suggested that inland waters are a large and growing global N₂O source, but whether, how, where, when, and why inland-water N₂O emissions changed in the Anthropocene remains unclear. Here, we quantify global N₂O formation, transport, and emission along the aquatic continuum and their changes using a spatially explicit, mechanistic, coupled biogeochemistry–hydrology model. The global inland-water N₂O emission increased from 0.4 to 1.3 Tg N yr^–1 during 1900–2010 due to (1) growing N₂O inputs mainly from groundwater and (2) increased inland-water N₂O production, largely in reservoirs. Inland waters currently contribute 7 (5–10)% to global total N₂O emissions. The highest inland-water N₂O emissions are typically in and downstream of reservoirs and areas with high population density and intensive agricultural activities in eastern and southern Asia, southeastern North America, and Europe. The expected continuing excessive use of nutrients, dam construction, and development of suboxic conditions in aging reservoirs imply persisting high inland-water N₂O emissions.