What is it?
Nitrogen, like phosphorus, is an important nutrient for plant growth. In rivers and lakes, nitrogen can be dissolved in the water, attached to particles floating in the water and found in the bodies of all living organisms.
Forms of nitrogen in freshwater systems include inorganic nitrogen: nitrate (NO3), nitrite (NO2), ammonia (NH3) and ammonium (NH4). These inorganic forms of nitrogen are the most bioavailable, meaning they are most easily used and taken up by organisms that live in the water. Other forms of nitrogen include organic nitrogen. Kjeldahl nitrogen includes ammonia, ammonium and organic nitrogen together.