Ammonia emissions from mudflats of river, lake, and sea

Whether mudflats are an important source of atmospheric ammonia (NH3) remains an open question, despite the fact that over half of the world’s population live within 3 km of surface water bodies. Here, we established three sites (lake, river, and sea) that are representative of tide-influenced mudflats across the Yangtze Delta in eastern China. Online field measurements of NH3 and auxiliary hydrometeorological parameters were simultaneously performed over a 9 month period. Surprisingly, the average NH3 concentrations measured at these locations are as low as regional background levels. No pulses of increased NH3 were found at these sites when mudflats were exposed due to receding water levels. High atmospheric NH3 concentrations are persistently associated with high temperatures, but their geographical origins have no overlap with the locations of water bodies. The potential mechanism is also discussed. Collectively, we provide the first direct observational evidence concerning mudflat as a source of NH3.