An international team of scientists has discovered a non-microbial process that generates nitrous oxide (N2O), a gas with a global warming potential 273 times greater than that of carbon dioxide. This mechanism, which the researchers have named “photochemodenitrification”, uses nitrites and nitrates as substrates in both freshwater and marine surface waters and is caused by sunlight. The discovery, which has just been published in the journal Science, could modify current calculations of global N2O emissions and improve strategies to mitigate climate change.
The study demonstrates that sunlight abiotically promotes the production of nitrous oxide in surface waters, and that this production can even exceed biological production of N2O through ammonium oxidation, the latter being considered the main source of N2O in surface waters. This process, which had not been described until now, is a new source of N2O that could help explain current uncertainties in global N2O emission estimates.
Main ozone-depleting agent
The researchers conducted experiments in the waters of the Cubillas (Granada) and Iznájar (Córdoba) reservoirs, as well as in the Mediterranean Sea (Motril coast, Granada) and the Baltic Sea (Boknis Eck, Germany). Using isotopic tracers such as 15N-Nitrite and 15N-Nitrate, they identified that nitrite is the main substrate of the reaction, while nitrate can also be transformed into N2O after its photochemical conversion into nitrite, all occurring without any biological activity.
Nitrous oxide is not only a potent greenhouse gas, but also the main ozone-depleting agent. Its abiotic production in aquatic ecosystems could contribute significantly to global emissions, especially in regions with intense solar radiation and large concentrations of inorganic nitrogen, such as coastal areas or eutrophic inland waters. It is important to note that, although this process is natural, its production is significantly stimulated by nitrogen inputs from human activities, like biological production.
The production of N2O through “photochemodenitrification” is higher at the water surface and decreases with depth due to light attenuation. This suggests that “photochemodenitrification” could have a disproportionate impact on N2O fluxes to the atmosphere compared to other reactions. This is because newly formed N2O at the air/water interface can diffuse more rapidly into the atmosphere compared to N2O produced and stored in the deeper layers of the water column (as typically occurs with biological production).
This discovery represents a crucial breakthrough in gaining a better understanding of the global N2O cycle and reducing uncertainties in emission estimates. The authors also emphasize the need to further investigate climate change processes, as it remains one of the most significant environmental challenges we face today.
The study, led by researcher Elizabeth León Palmero and initiated during the development of her doctoral thesis at the Department of Ecology of the University of Granada under the direction of professors Isabel Reche and Rafael Morales Baquero, was completed during her postdoctoral stage at the University of Southern Denmark, where she worked with Carolin Löscher and Bo Thamdrup.
This research work has been funded by the Spanish Ministry of Education, Culture and Sport, the Ministry of Science, Innovation and Universities, and the Spanish Association of Terrestrial Ecology- Iberian Society of Ecology (AEET-SIBECOL).
Contact
Elizabeth León Palmero
Email: eleonpalmero@ugr.es
Web: https://eleonpalmero.com
Translated version: This text has been translated into English by the principal investigator of this scientific work.
