The harmful effects of nitrogen-containing fertilisers on aquatic ecosystems are well-documented around the world. Nitrogen pollution affects many types of aquatic ecosystems, including freshwater, brackish, and coastal marine environments. High nitrogen concentrations may also contaminate drinking water supplies. Heavy use of nitrogen fertilisers in agricultural areas causes runoff into waterways, which leads to nitrogen pollution. According to a report from the Ecological Society, nitrogen pollution causes "changes in the composition and functioning of [aquatic] ecosystems and contributes to long-term declines in coastal marine fisheries" and biodiversity. Nitrogen fertilizers contribute to the acidification of freshwater, causes extreme plant growth, and can accumulate to toxic levels.
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Acidification of Freshwater
When nitrogen combines with freshwater, it releases hydrogen ions and ammonia into the water. The presence of hydrogen and ammonia increases the acidity of freshwater by lowering its pH. According to research conducted by the Universidad de Alcalá and the INIA in Madrid, Spain, "eastern North America and northern and Central Europe are major acidified regions on Earth."
Acidification severely reduces the biodiversity of aquatic ecosystems. According to the United Kingdom's Atmosphere, Climate, and Environment Information Programme, acidification causes freshwater to become bluer and clearer. The amount of life in the water stays the same but certain species do not survive. For example, species such as the mayfly will vanish while dragonfly larvae and bloodworms do unusually well in acidified water without the competition of the mayflies.
Excessive Plant Life
When too much nitrogen is present in aquatic ecosystems, plant life first flourishes and then begins encroaching on all other life in the ecosystem. This occurrence is referred to as "eutrophication." The abundance of plants begins consuming more oxygen than what is available and other species begin suffocating because of no-oxygen (referred to as "anoxia") or low-oxygen levels (referred to as "hypoxia").
Areas of low or no oxygen are called "dead zones" and occur worldwide. Prominent marine dead zones are located off the coast of Oregon, in the Chesapeake Bay and in the Gulf of Mexico. According to NASA, although several natural dead zones exist (e.g., the Black Sea), "the apparent cause of the creeping dead zones is agriculture, specifically fertiliser."
The accumulation of nitrogen in aquatic environments can produce high levels of nitrogen-based byproducts such as:
--Ammonia, which is especially toxic to fish because it damages their gills --Nitrite, which enters the bloodstreams of fish and invertebrates and prevents them from using oxygen --Nitrate, to which freshwater fish species and amphibians are especially sensitive
According to the Universidad de Alcalá and INIA, "current field data suggests that nitrogen-based fertilisers may be contributing to the decline of amphibians in agricultural areas."
Groundwater contaminated with nitrogen can harm humans, especially infants, by inhibiting the oxygen-carrying function of the blood and may play a role in birth defects and digestive system cancers.
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- United Kingdom's Atmosphere, Climate and Environment Information Programme; Encyclopedia of the Atmospheric Environment
- Universidad de Alcalá and Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA); Ecological and toxicological effects of inorganic nitrogen pollution in aquatic ecosystems: A global assessment
- Ecological Society; Human Alteration of the Global Nitrogen Cycle: Sources and Consequences
- NASA; Science Focus: Dead Zones