Nitrification
Nitrification is a microbial process that oxidizes ammonia or ammonium first to nitrite and then to nitrate in oxygen-rich environments.
What nitrification is
Nitrification is the biological oxidation of reduced nitrogen compounds. In the classic two-step pathway, ammonia or ammonium is oxidized to nitrite, and nitrite is oxidized to nitrate. The process is carried out by specialized bacteria and archaea.
Two linked steps
The first step is ammonia oxidation, often performed by ammonia-oxidizing bacteria or archaea. The second step is nitrite oxidation, performed by nitrite-oxidizing bacteria. Some microbes called comammox organisms can complete both steps by themselves.
Why oxygen is important
Nitrification is usually an aerobic process because oxygen is part of the chemistry that oxidizes ammonia and nitrite. It tends to be strongest where oxygen, ammonia, moisture, and suitable surfaces or soils are all available.
Part of the nitrogen cycle
Nitrification changes nitrogen into nitrate, a form that plants and microbes can use but that also moves easily with water. It connects ammonification, plant uptake, leaching, and denitrification, which can return nitrate-derived nitrogen to the atmosphere.
Soils and agriculture
In soils, nitrification can make nitrogen more available to crops, but it can also increase nitrate leaching if plants do not take it up. Fertilizer timing, soil temperature, pH, moisture, and oxygen all influence how quickly ammonia becomes nitrate.
Wastewater and biofilters
Wastewater treatment plants use nitrification to convert ammonia, which can harm aquatic life, into nitrate. Aquariums and drinking-water biofilters also rely on nitrifying microbes growing on surfaces, where water brings ammonia and oxygen to the community.
Environmental tradeoffs
Nitrification can improve water quality by lowering ammonia, but it may also produce nitrate that fuels eutrophication if not removed. Under some conditions, nitrifying microbes can contribute to nitrous oxide emissions, linking the process to climate concerns.
Why it matters
Nitrification is a small microbial process with large consequences. It helps explain how nitrogen moves through soils, streams, farms, treatment systems, and aquariums, and why managing oxygen and nitrogen forms matters for ecosystems.