The widespread use of synthetic fertilizers has increased the amount of reactive nitrogen in the environment, highlighting the vital role microbes play in returning nitrogen to the atmosphere as nitrogen gas. Photo Credit: Fuka jaz / Pexels
Nitrogen is essential for life, but when excessive amounts enter rivers, lakes and coastal waters, it can damage ecosystems and threaten aquatic organisms. Microorganisms help control this problem by converting nitrogen compounds into nitrogen gas, which escapes into the atmosphere. Despite the importance of this natural process, determining how much nitrogen is removed by microbes has remained a significant challenge for scientists.
A research team from UC Santa Barbara, UCLA and collaborating institutions has developed a new approach that uses a rare isotopic signature in nitrogen gas to measure microbial nitrogen removal. Published in Science, the study introduces a method that could help researchers detect nitrogen loss that conventional techniques may overlook and improve estimates of how nitrogen moves through the environment.
The method takes advantage of subtle differences in the atomic composition of nitrogen gas. Nitrogen occurs primarily as two isotopes: nitrogen-14, the more abundant form, and nitrogen-15, which contains an additional neutron. Although most nitrogen gas molecules contain two nitrogen-14 atoms, a small fraction contain two nitrogen-15 atoms. The relative abundance of these heavier pairs differs between atmospheric nitrogen and nitrogen produced by microorganisms.
Atmospheric nitrogen contains an unusually high proportion of molecules with two nitrogen-15 atoms, while microbial processes produce nitrogen gas with isotope pairings closer to random. When these sources mix, the distinctive atmospheric pattern changes. By measuring these differences, researchers can identify the contribution of microbial activity and estimate how much nitrogen has been removed from an ecosystem.
First author Jiarui Liu conducted the research as a postdoctoral fellow at UC Santa Barbara’s Marine Science Institute and UCLA. Liu and David Valentine are principal investigators at UC Santa Barbara’s Marine Science Institute. Valentine, who holds the Norris Presidential Chair of Biogeochemistry, also served as Liu’s postdoctoral advisor at UCSB.
To detect this subtle isotopic signal, the team analyzed nitrogen gas extracted from water and sediment samples using UCLA’s Panorama mass spectrometer. The instrument separates molecules according to their mass and electrical charge. Because the rare nitrogen molecules have masses very similar to those of other molecules, identifying them requires highly precise instrumentation. Panorama’s advanced capabilities allow researchers to distinguish these small differences and measure the isotopic signature.
The research brought together scientists specializing in groundwater, lakes and marine environments. The team tested the approach across a wide range of locations, including groundwater in Texas, lakes in Antarctica and Minnesota, coastal basins off Southern California, the Bay of Bengal and deep-sea sediments offshore from Alaska. This broad application demonstrates the method’s potential for investigating nitrogen cycling across diverse ecosystems.
Researchers found that microbial mats at methane seeps, such as this site off Southern California, may play an important role in transforming nitrogen compounds into nitrogen gas. Photo Credit: Woods Hole Oceanographic Institution/Submersible Alvin
The findings have important implications for understanding and managing nitrogen pollution. Agricultural fertilizers, wastewater discharge and other human activities introduce additional nitrogen into aquatic environments. Excess nutrients can promote harmful algal blooms, and when the algae decompose, the resulting oxygen depletion can create conditions that endanger fish and other aquatic life.
By measuring how much nitrogen microorganisms naturally remove, scientists could better evaluate the fate of nitrogen pollution before it reaches sensitive ecosystems. The technique may also help determine whether groundwater microbes reduce nitrate contamination or whether nitrogen continues downstream into lakes, rivers and coastal waters, where it can contribute to algal growth.
The approach could also improve groundwater monitoring. Many routine monitoring programs do not account for nitrogen gas generated within aquifers, potentially leading to incomplete estimates of nitrogen sources and removal. Co-author Alan Seltzer, an assistant professor of hydrogeology at University College Dublin, has highlighted the importance of measuring this overlooked pathway to develop a more comprehensive understanding of nitrogen movement through groundwater systems.
Beyond local pollution, the research could help scientists refine the global nitrogen budget. This budget tracks the balance between processes that supply biologically available nitrogen and those that remove it from ecosystems. Understanding that balance is essential for assessing nutrient availability and the functioning of food webs worldwide.
By combining isotopic measurements with information about water movement and nitrogen gas accumulation, researchers can estimate nitrogen-removal rates at the ecosystem level. Applying the method across different environments could connect local measurements to regional and global assessments, helping scientists determine how nitrogen cycling changes over time.
Although the technique requires specialized equipment and is not yet suited to routine field monitoring, it offers a valuable new tool for environmental research. By revealing a previously difficult-to-measure aspect of the nitrogen cycle, the study advances scientific understanding of how natural processes help limit pollution and maintain healthier aquatic ecosystems.
Adapted from original reporting by Harrison Tasoff, “A rare atomic fingerprint reveals how ecosystems clean nitrogen pollution,” The Current, UC Santa Barbara, 2026, in collaboration with Holly Ober at UCLA.