Contaminated aquifers are a forgotten component of the global N2O budget

Abstract

One of the chemical components contributing to the destruction of the ozone layer in the upper atmosphere consists of the nitrogen oxides formed from N2O (ref. 1). Prompted by the prevailing idea that the ocean is not a major source of N2O or a sink for N2O, estimates have been made of global fluxes from continental ecosystems2. Although most land areas are underlain by groundwater3, this medium has never been considered in global budgeting of N2O. A large number of aquifers around the world are contaminated by nitrogen compounds, and processes of nitrification and denitrification are reported to be operative in this environment3. These processes lead to the production of N2O (refs 4 and 5). Here we report that the concentration of N2O in phreatic aerobic aquifers contaminated by anthropogenic activities (disposal of human or animal waste, cultivation and fertilization) are up to three orders of magnitude higher than the concentration expected as a result of equilibrium with the atmosphere.