Total Nitrogen is the sum of nitrate (NO3), nitrite (NO2), organic nitrogen and ammonia (all expressed as N). Note that for laboratory analysis purposes, Total Kjeldahl Nitrogen (TKN) is a test performed that is made up of both organic nitrogen and ammonia.
the sum of all forms of nitrogen (both dissolved and particulate) in water
A measure of all forms of nitrogen (for example, nitrate, nitrite, ammonia-N, and organic forms) that are found in a water sample.