Nitrogen is an essential element for all plants and animals. Seventy-nine percent of air is made up of nitrogen in its molecular form (N2), however, this form cannot be readily assimilated by most plants. Only bluegreen algae and some bacteria are able to use nitrogen in its molecular form and convert it to forms that can be taken up by plants. Aquatic animals obtain nitrogen for protein building either by consuming aquatic plants directly, or feeding on other plant eating animals.
When aquatic plants and animals die, large protein molecules are broken down to ammonia by bacteria. Ammonia is then oxidized to form nitrites and nitrates. Animal excretions are very rich in ammonia, but the amount of ammonia added to water systems through animal excretions is small. However, in areas where duck and geese are plentiful a heavy load of nitrogen can be added to the water. Nitrogen that was previously "locked up" is released through the decomposition of dead plants and animals, and the excretions of living animals.
Sources of Nitrates
Nitrate is a natural substance found in water and plants. Sources associated with people and their activities include municipal and industrial wastewaters, refuse dumps, urban drainage, animal feed lots, septic systems and leachate or runoff from manure or from fertilized lands. Nitrogen in the form of nitrates and ammonia acts as a nutrient, and is one of the nutrients sometimes responsible for eutrophication. It is second only to phosphorus as the nutrient most responsible for promoting aquatic plant growth. Nitrates also can cause groundwater contamination. They are of concern not only because of their toxic potential in high concentrations (>10 mg/l N03-N) but also because they may be an indication of other contaminants in the groundwater.
