Industries that use nitrates in manufacturing may release nitrate in the effluent water. The primary nitrogen source in the western United States is agricultural fertilizers. Atmospheric deposition is the second-most prevalent source. The central and southeastern United States also primarily derive nitrogen pollution from agricultural fertilizers. The second-most prevalent source is animal manure.
Overland flow is the most direct route for water transportation.
Underground flow is less direct because water flow is impeded by soil permeability and porosity constraints. The combustion of fossil fuels and the discharge of agricultural and industrial nitrogen-containing compounds into the atmosphere has allowed gases, aerosols, and fine particles to be borne by wind and deposited either directly into the water body or carried from the atmosphere to the water body via precipitation. Nitrites in soil are readily oxidized to nitrate. The nitrite concentration is determined by diazotizing with sulfanilamide and coupling with NED dihydrochloride to form a colored azo dye that is measured colorimetrically. Nitrate is determined potentiometrically using an NH3 gas-sensing electrode after nitrate is reduced to NH3 by a titanous chloride reagent.