Nitrogen Cycle in Water
Nitrates (N)3) are an essential nutrient for plant growth and
are a main ingredient in fertilizers. Rain can wash nitrates from farm fields,
lawns, golf courses, or other fertilized lands into streams. In nature, nitrates
are formed by bacteria breaking down ammonia and other compounds that contain
nitrogen. Bacteria may also create nitrates as they decompose dead animals,
plants, or fecal wastes.
Too much nitrate can cause problems such as excessive algal and
plant growth. Nitrates in drinking water can be a health hazard. Most experts
agree that safe drinking water should have less than 10 mg/liter of nitrate.
Concentrations of nitrate-nitrogen greater than 90 mg/liter can be directly
harmful to many aquatic animals. Some, especially those such as salmon, that
prefer cold water have lower tolerances to nitrate.
Causes of Nitrogen Pollution in Surface
Waters:
*Nitrogen can come from manure sources, such as treatment lagoons
and overfertilized fields.
*In commercial inorganic fertilizers, nitrogen is used in the
greatest quantities of any nutrient. Runoff from agriculture, forestry, golf
courses, and lawns is high in nitrogen, especially if runoff occurs shortly
after fertilizer applications.
*Ammonia comes from the decomposition of organic matter, especially
in the absence of oxygen.
*Municipal and industrial wastewaters can contain either ammonia
or nitrate.
*Contaminated groundwater seeping into streams may be a source
of nitrogen. Such groundwater may be contaminated by sewage which enters the
ground via septic tanks in rural communities.