Characterizing ammonia emissions from water bodies using dynamic floating chambers

Ammonia (NH₃) is the most important alkaline gas in the atmosphere and plays a central role in atmospheric pollution and the global N cycle. Water bodies receive increasing nitrogen inputs from effluents and atmospheric deposition due to anthropogenic activities and are regarded as the major natural NH₃ and NH₄⁺ sinks. In this work, floating dynamic flux chambers were deployed at four types of freshwater (rivers, large reservoirs, medium-sized reservoirs and ponds) systems and a coastal seawater system to estimate the water-air NH₃ emission fluxes. The NH₃ emission fluxes of rivers (26.4 μg NH₃ m^-2 h^-1) were significantly higher than those of other types of freshwater systems, and the NH₃ flux of offshore water was unexpectedly high (3.9 μg NH₃ m^-2 h^-1). The ammonium content and water temperature were the most important factors driving NH₃ emissions from water bodies. The global NH₃ emissions from water bodies reached 8.88 TgN a^-1, and this value will increase persistently with global warming and water quality deterioration. Water bodies that are relatively eutrophic and directly affected by anthropogenic activities should be considered reservoirs of inputted N instead of permanent sinks.