USDA LTAR Common Experiment measurement: Dissolved ammonia (NH3) concentration v1

Ammonia can form naturally from organic matter mineralization or can enter the aquatic environment via anthropogenic sources such as municipal effluent discharge and agricultural runoff. The presence of ammonia (NH3) vs. ammonium (NH4+) in water depends on water pH and temperature. The un-ionized NH3 form is toxic to aquatic organisms, and both forms (NH4+ and NH3) can contribute to eutrophication and hypoxia of surface waters. The reported measurement of ammonia in water is typically the total ammonia N (TAN = NH3 + NH4+). The recommended techniques for measuring NH3 in water are the colorimetric salicylate and phenate methods, whereby an indophenol color complex is proportional to the NH3 concentration of the sample.