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Nitrates in Aquatic Ecosystems

Nitrates are produced and used in aquatic ecosystems through a process called the nitrogen cycle. In that cycle, plant and animal byproducts first break down to produce ammonia. Bacteria within the water oxidize that ammonia to produce nitrites, and then other bacteria colonies oxidize the nitrites to produce nitrates. The nitrates are then used as a fertilizer for blue-green algae and aquatic plants, which enables the plants and blue green algae colonies to grow and perform photosynthesis. The plants become food for aquatic animals, which produce ammonia-rich waste, and the nitrogen cycle begins again.

Plant and Animal Byproducts Produce Ammonia
- The protein in dead organic matter, such as in dead aquatic plants and animals, breaks down into ammonia as the organic matter decays. Waste from living aquatic animals, as well as the waste of terrestrial animals that streams into waterways, also contains ammonia. Ammonia is toxic to all aquatic animal life. Meanwhile, as the proteins and waste break down into ammonia, the living plants within the aquatic ecosystem release oxygen into the water as a byproduct of their photosynthesis.
Bacteria Colonies Oxidize Ammonia to Produce Nitrites
- Colonies of aquatic nitrosomonas bacteria within the water bind the ammonia in the water with the oxygen released by the plants and the oxygen that is mixed into the water from the air through the movement at the water's surface. The oxidized ammonia that the nitrosomonas produce is called nitrite, also called NO2. Like ammonia, nitrites are also toxic to aquatic animal life. The nitrosomonas bacteria oxidize the ammonia in order to gain energy through the oxidation, which they use to fuel their metabolic
Bacteria Colonies Oxidize Nitrite to Produce Nitrates
- Colonies of aquatic nitrospira bacteria then bind another oxygen to the nitrite, to produce nitrate, which is also annotated as NO3. Though, like nitrates and ammonia, nitrate is also toxic to aquatic animal life, it is relatively neutral when compared to those chemicals. It is also in the form of nitrogen that can be directly absorbed by plants and cyanobacteria.
Blue-Green Algae and Plants Metabolize Nitrates to Produce Amino Acids
- Cyanobacteria, which are also called blue-green algae, are aquatic bacteria that performs photosynthesis. Though individual cyanobacteria are single-celled organisms, they grow in colonies that can become so large they're visible to the naked eye. A cyanobacterium also makes up the plant cell's chloroplast, which is what allows the plant to perform photosynthesis. Cyanobacteria and aquatic plants absorb nitrates from the water, and use them to form amino acids. Amino acids make up protein molecules, and protein is an essential building block of life. The nitrate acts as a fertilizer for the aquatic plants. The plants then become food for the aquatic animals, which produce ammonia-rich waste. Dead plant matter left over from feeding also releases ammonia into the aquatic ecosystem, fueling the nitrogen cycle.

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