Doubly heavy nitrogen molecules expose the nitrogen gas microbes add to water
Researchers at UCLA and UC Santa Barbara report in Science that the rare 15N15N form of nitrogen gas tracks how much nitrogen microbes convert to gas. Air dissolved in water normally hides that microbial gas, so the signal shows nitrogen removal that conventional methods obscure.
The Scientist · Science desk
What happened
- Air's nitrogen gas holds more molecules with two nitrogen-15 atoms than chance predicts, while microbial gas pairs its atoms almost at random and dilutes that surplus as it mixes in.
- The team measured gas extracted from water and sediment on UCLA's Panorama mass spectrometer, whose large size lets it separate the rare molecule from others of almost the same mass.
- Groundwater, lake and marine researchers applied it to Texas groundwater, lakes in Antarctica and Minnesota, Southern California coastal basins, the Bay of Bengal and deep-sea sediments off Alaska.
Why it matters
- What it limits constraint The measurement depends on sophisticated machinery, so routine field monitoring will keep its current methods for some time and research groups will be the first users.
- What's now possible capability Researchers can now set estimates of fertilizer and wastewater nitrogen inputs against a measured figure for what microbes remove on their own.
- What it sets up precedent Seltzer's European Research Council grant, TabPhish, builds on the UCLA collaboration, so groundwater nitrogen cycling is the likely next test of the method.
Next story · Build · yesterday
Google's Willow chip cultivates magic states with about 40x fewer errorsConfirmed5 publishers
"The problem is that our water naturally has a huge amount of nitrogen gas that is dissolved from the air, so the gas that microbes produce can be very difficult to see," said Jiarui Liu, the first author, who did the work as a postdoctoral fellow at UCSB's Marine Science Institute and at UCLA [3]. "The answer is written in the way nitrogen atoms are paired inside the nitrogen molecule," Liu said [4].
It is a tidy design. The signal comes from the rarest form of nitrogen gas. Most N2 holds two nitrogen-14 atoms, some holds one of each isotope, and very rarely both atoms are nitrogen-15 [6]. Microbial gas lowers air's surplus of that molecule. So the dissolved air that hides the microbial product also sets the baseline the microbial share is read from [5]. The 15N15N the method relies on is naturally present in the water's gas [2]. "At UCLA, we discovered the anomalous pairing of heavy nitrogen atoms in Earth's atmosphere and are now making use of this signature of nitrogen in air as a powerful and unique geochemical tool," said Edward Young, a UCLA geochemist, co-author and Liu's postdoctoral adviser [8].
According to the phys.org account, the study reveals microbial nitrogen loss that conventional methods obscure [10]. The thing the published accounts don't tell you is how large that hidden loss is, at any of the six settings sampled or across them [18]. Without a size, the reports cannot show how far water-quality assessments or the global nitrogen budget would move. I think the reported evidence supports the narrower claim: a method shown to work in very different waters, with the size of the correction still unmeasured. The phys.org account itself calls the method "a new tool to improve water-quality assessments and estimates of the global nitrogen budget" [9].
Fertilizer runoff and wastewater add nitrogen that fuels harmful algal blooms. As the blooms decay they consume oxygen and can leave low-oxygen dead zones [14]. "We want to understand whether microbes in groundwater can mitigate nitrate pollution, and how much nitrogen is removed along the way before it can fuel algal growth in lakes, rivers and coastal waters," Liu said [11].
"Many routine groundwater-quality monitoring programs do not measure the N2 gas produced within an aquifer, which can create substantial biases in our accounting of where nitrogen comes from and where it goes," said Alan Seltzer, an assistant professor of hydrogeology and groundwater systems at University College Dublin and a co-author [12][13].
What to watch
- Site-by-site figures comparing 15N15N-based estimates of microbial nitrogen loss with conventional estimates from the same waters.
- First groundwater results from Seltzer's TabPhish project with UCLA, and whether counting in-aquifer N2 shifts estimates of where nitrate comes from.
- Whether instruments other than UCLA's Panorama can resolve 15N15N well enough for other labs to run the method.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence50
- Adoption5
- Hype gap+15
- Incentives45
- Confidence60
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
Biogeochemists at UC Santa Barbara, UCLA and collaborating institutions have shown that a rare form of nitrogen gas can act as a natural fingerprint for microbial nitrogen conversion, in a study published in Science.
- [2]
According to the study, the rare, naturally found 15N15N isotopologue can be used to determine the amount of nitrogen production in water.
- [3]
"The problem is that our water naturally has a huge amount of nitrogen gas that is dissolved from the air, so the gas that microbes produce can be very difficult to see," said first author Jiarui Liu, who conducted the research as a postdoctoral fellow at UCSB's Marine Science Institute and at UCLA.
- [4]
"The answer is written in the way nitrogen atoms are paired inside the nitrogen molecule."
- [5]
In atmospheric nitrogen gas, two heavy nitrogen-15 atoms pair up more often than expected by chance, while nitrogen gas produced by microbes has atoms paired nearly at random; when microbial nitrogen mixes with air nitrogen it reduces that excess of heavy pairs, so the relative abundance of the rare molecule can reveal how much nitrogen gas was produced by microbial activity.
- [6]
Most N2 molecules contain two nitrogen-14 atoms; some contain one of each isotope; and very rarely, both atoms are nitrogen-15.
- [7]
The team measured nitrogen gas extracted from water and sediment samples using UCLA's Panorama mass spectrometer; the rare nitrogen pairs are usually hard to distinguish because other molecules have almost exactly the same mass, but Panorama's unusually large size enables it to separate them.
- [8]
"At UCLA, we discovered the anomalous pairing of heavy nitrogen atoms in Earth's atmosphere and are now making use of this signature of nitrogen in air as a powerful and unique geochemical tool," said geochemist Edward Young, a co-author and Liu's postdoctoral adviser at UCLA.
- [9]
The technique requires sophisticated machinery, so it won't find its way into routine field monitoring anytime soon; however, it offers a new tool to improve water-quality assessments and estimates of the global nitrogen budget.
- [10]
The study reveals microbial nitrogen loss that conventional methods obscure.
- [11]
"We want to understand whether microbes in groundwater can mitigate nitrate pollution, and how much nitrogen is removed along the way before it can fuel algal growth in lakes, rivers and coastal waters," Liu said.
- [12]
"Many routine groundwater-quality monitoring programs do not measure the N2 gas produced within an aquifer, which can create substantial biases in our accounting of where nitrogen comes from and where it goes."
- [13]
The study was co-authored by University College Dublin's Dr Alan Seltzer, an assistant professor of hydrogeology and groundwater systems.
- [14]
Fertilizer runoff, wastewater discharge and other human activities add excess nitrogen that can degrade water quality and fuel harmful algal blooms; as blooms die off their decay consumes oxygen and can create low-oxygen dead zones.
- [15]
Seltzer was recently awarded a European Research Council Starting Grant for a project called TabPhish that traces groundwater, focusing on water level changes and nitrogen cycling; the research will expand on his collaboration with UCLA.
- [16]
By measuring how much nitrogen microbes remove naturally, the approach can help assess fertilizer and wastewater inputs and inform efforts to protect water quality.
- [17]
The study brought together groundwater, lake and marine researchers and applied the approach to Texas groundwater, lakes in Antarctica and Minnesota, coastal basins off Southern California, the Bay of Bengal and deep-sea sediments offshore from Alaska.
- [18]
The study sampled six field settings.
Sources
2 independent publishers whose own reporting we read for this story.
- phys.orgWhere does Earth's nitrogen go? Two atoms offer a clue
1 article · October 9, 2026
- siliconrepublic.comRare nitrogen molecule could be key to better water quality testing
1 article · October 9, 2026
Topics and entities
Topics
- Nutrient pollution
- Water quality monitoring
- Isotope Geochemistry