Determining Sources and Cycling of Nitrate in an Agricultural Catchment Using δ15N and δ18O in Nitrate

Understanding the nitrogen cycle is increasingly important. Humans have more than doubled the annual global production of reactive nitrogen, negatively impacting water quality, and terrestrial and coastal ecosystems. Agricultural activity is a major source of anthropogenic reactive nitrogen. It accounts for 75% of anthropogenic fixed nitrogen and comes primarily from the production of nitrogen fertilisers. However, a poor understanding of the nitrogen cycle in agricultural environments results in the loss of nearly three quarters of agricultural nitrogen to water and the atmosphere rather than contributing to food production. Nitrification and denitrification play key roles in the loss of agricultural nitrogen. Nitrification transforms ammonium to nitrate. Nitrate is the form of fixed nitrogen which is most readily lost, via denitrification in gaseous forms, or as dissolved nitrate exported in st