Effects of Ammonia Deposition

On a global basis, the deposition of ammonia to continents has increased about 4-fold, from ~11 Tg N/ yr in 1860, to ~39 Tg N/yr in the mid-1990s. The primary driver of the increased deposition is food production, especially animal production. The most immediate effect of additional ammonia deposition is altered productivity of N-limited terrestrial and aquatic ecosystems. In addition, as the deposited N atom cascades through environmental reservoirs, there are numerous secondary and tertiary effects. In addition to impacting productivity, the deposited N can also increase soil acidity and decrease biodiversity. If the N atom is discharged to an aquatic ecosystem, it can increase surface water acidity, and then lead to coastal eutrophication. If the N atom is converted to N₂O, and emitted back to the atmosphere, it can then first increase greenhouse warming potential, and then decrease stratospheric ozone. The only effective way to reduce the magnitude of these effects is to decrease ammonia deposition by adopting a total-system approach to N management in food and energy production.