Nitrification in the marine environment
In the
marine environment, nitrogen is often the
limiting nutrient, so the
nitrogen cycle in the ocean is of particular interest.
[11][12] The nitrification step of the cycle is of particular interest in the ocean because it creates
nitrate, the primary form of nitrogen responsible for
"new" production. Furthermore, as the ocean becomes enriched in
anthropogenic CO2, the resulting decrease in
pH could lead to decreasing rates of nitrification. Nitrification could potentially become a "bottleneck" in the nitrogen cycle.
[13]
Nitrification, as stated above, is formally a two-step process; in the first step
ammonia is
oxidized to
nitrite, and in the second step nitrite is oxidized to nitrate. Different microbes are responsible for each step in the marine environment. Several groups of ammonia oxidizing bacteria (AOB) are known in the marine environment, including
Nitrosomonas,
Nitrospira, and
Nitrosococcus. All contain the functional gene
ammonia monooxygenase (
AMO) which, as its name implies, is responsible for the oxidation of ammonia.
[12] More recent
metagenomic studies have revealed that some
Crenarchaeote Archaea possess AMO. Crenarchaeote are abundant in the ocean and some species have a 200 times greater affinity for ammonia than AOB, leading researchers to challenge the previous belief that AOB are primarily responsible for nitrification in the ocean.
[14] Furthermore, though nitrification is classically thought to be vertically separated from
primary production because the oxidation of nitrogen by
bacteria is inhibited by light, nitrification by AOA does not appear to be light inhibited, meaning that nitrification is occurring throughout the
water column, challenging the classical definitions of
"new" and "recycled" production.
[14]
In the second step, nitrite is oxidized to nitrate. In the ocean, this step is not as well understood as the first, but the bacteria
Nitrospina and
Nitrobacter are known to carry out this step in the ocean.
[14]
it works pretty much the same as this in our aquaponics systems
