Atmospheric Hydrogen Variability in Flooded Areas of the Yangtze River Delta

Terrestrial aquatic ecosystems may constitute substantially underestimated sources of atmospheric H 2, an indirect greenhouse gas with growing significance as the hydrogen economy expands. We conducted a 22 month observational campaign across three sites in China’s Yangtze River Delta: a regional background station (LAN), a site with extensive lakes (LK), and a paddy field and a wetland-dominated site (PF-WL). Mean H 2 concentrations at LK and PF-WL (1454 and 1503 ppb) were all 2.5–2.6 times higher than the global average. Critically, ΔH 2 /ΔCO ratios at LK (1.22) and PF-WL (1.98) substantially exceeded the conventional combustion range (0.27–0.9), while strong H 2 –CH 4 correlations (Pearson's r = 0.33–0.44) identified flooded ecosystems as potential H 2 sources. At LAN, soil processes dominated with summer peaks driven by temperature–precipitation interactions. LK appeared to reflect mixed anthropogenic and lake sediment influences, whereas PF-WL was more strongly influenced by a combination of anthropogenic emissions and emissions from rice paddies and wetlands. Our findings suggest that aquatic ecosystem emissions may represent an important but previously underappreciated component of regional H 2 budgets and that excluding them could introduce substantial uncertainty into hydrogen inventories in monsoon-affected subtropical regions.