Nitrogen is one of the primary biogenic elements responsible for the eutrophication of surface waters. It is part of many compounds and has a relatively complex cycle of circulation in nature. Analyses of water fertility and eutrophication mainly focus on nitrogen bound in nitrate and ammonium ions. The other compounds of this element – nitrites, amines and the like – are taken into account less frequently, mainly as components of the so-called “nitrites”. Mineral and organic nitrogen. Analysis of the gaseous forms of this element – oxides and molecular nitrogen, called atmospheric nitrogen – appears in works on its circulation.