The main inorganic nitrogen species in rivers are ammonium, nitrite and nitrate. Contamination of water by anthropogenic nitrate has become a global environmental concern and the measurement of nitrogen isotope ratios of nitrate is an effective method for identifying and differentiating between natural and anthropogenic nitrate sources and it provides opportunities to study the nitrogen cycle. However, established methods for determining the nitrogen isotopic composition of nitrate at natural abundance levels are demanding and often hinder rapid and reliable measurements required in water monitoring programs. A variety of methods is used for the determination of the nitrogen isotope signature of nitrate in water: