Researchers have revealed a groundbreaking method that enables the assessment of biological loss of fixed nitrogen by utilizing an unexplained anomaly in atmospheric dinitrogen’s isotopic makeup. This development could provide insights into fundamental queries regarding the global nitrogen cycle and might help tackle issues like groundwater remediation.
Reactive nitrogen generally enters the biosphere via nitrogen-fixing bacteria, archaea, or occasionally through lightning. Human actions, such as the application of fertilizers, also play a role in this process, with a significant portion of the nitrogen washing into water bodies and eventually into oceans. Anaerobic microbes typically eliminate this nitrogen by converting it back into nitrogen gas or other less benign compounds like nitrous oxide. Accurately measuring biological dinitrogen production is essential for grasping Earth’s ecology and the effects of human activities on it.
Identifying biogenic nitrogen signals poses a challenge, as Earth’s atmosphere is composed of 78% nitrogen. A prevalent method involves using argon as an inert reference standard for air, presuming that an increase in the nitrogen-to-argon ratio indicates biogenic nitrogen production. However, argon is considerably more water-soluble than nitrogen, which may distort the findings.
In 2017, a team led by planetary scientist Edward Young at UCLA utilized a mass spectrometer named Panorama to demonstrate that dimers of two rare nitrogen-15 atoms occur about 2% more frequently than randomly anticipated in atmospheric dinitrogen. This anomaly is thought to result from photochemical processes occurring in the upper atmosphere. In contrast, isotopic pairing in biogenic dinitrogen is random, making it a dependable indicator of biologically produced dinitrogen.
Young and his team studied this signal across various regions, observing distinct differences in samples from diverse environments, such as urban and pristine lakes, along with variations in California’s coastal basins throughout the year. Few laboratories are capable of analyzing samples with the necessary precision to conduct these experiments, and the Panorama mass spectrometer is unparalleled in resolution.
This method could have profound implications for comprehending the global nitrogen cycle and tracking nitrate removal in groundwater. Ecosystem ecologist Peter Groffman commends the progress and aspires to use it to gauge biogenic nitrogen fluxes in terrestrial ecosystems, although hurdles persist.