What are Nitrates?
Nitrates in the water are from fertilizer runoff, leaky cesspools, sewage treatment plants, manure runoff, and car exhausts. In nature, they generally are formed by the action of bacteria on ammonia and on compounds which contain nitrogen. Nitrites are a relatively short-lived form of nitrogen that quickly become converted to nitrates by bacteria. However nitrites produce a serious illness ("brown blood disease") in fish even though they don't exist for very long in the environment. Nitrites also react directly with hemoglobin in the blood of people to produce met hemoglobin which destroys the ability of blood cells to transport oxygen. This condition is especially serious in babies under three months of age as it causes a condition known as methemoglobinemia or "blue baby" disease.
How nitrates affect aquatic life
Nitrates have the same effect on aquatic plant growth as phosphates and thus the same negative effect on water quality. The plants and algae are stimulated, which provide food for fish. This may cause an increase in the fish population. But, if algae grow too wildly, oxygen levels in the water will be reduced and fish will die.
Because nitrates can exist for short times in the altered form of nitrites, and because nitrites can cause serious illness to both wildlife and humans, acceptable nitrate levels for drinking water have been established as 10 mg/l. Unpolluted water generally has a nitrate reading of less than 1.0 mg/l.
More information on Nitrates and Nitrites
