AMES, Iowa – “The lake surface is calm, and the still air is glorious on this cool, cloudless August morning,” Iowa State University’s Elizabeth Swanner wrote about a research trip to a 60-foot deep, 13-acre lake within Itasca State Park and the Mississippi River headwaters of north-central Minnesota.
It’s true, she wrote, that park visitors generally don’t pay much attention to Deming Lake.
But Swanner and her research group, rowing across the surface, pay a lot of attention.
“Modest Deming Lake offers more than meets the eye for me,” wrote Swanner, an Iowa State professor of Earth, atmosphere and climate, in an October 2023 account of her field work published by The Conversation.
Now Deming Lake, surrounded by forest, and its urban cousin, Brownie Lake, just off Interstate 394 and a few miles west of downtown Minneapolis, are contributing measurements to a research study published in the journal Science.
Both lakes are meromictic, meaning they’re permanently stratified. Unlike 99% of all other lakes, their deepest waters never rise and mix with surface waters, and their surface waters never sink to the bottom. The stratification creates a low-oxygen environment at the bottom of the lake.
“These systems are unique,” Swanner said. “We can see the effects of processes much more clearly. These are good testbeds.”
Swanner usually studies the lakes’ deep water for clues about the Earth’s early oceans, which also lacked oxygen. But for this project, her research group took samples to measure an extremely rare version of dinitrogen gas containing two 15 N isotopes, a double-atom, clumped isotope of nitrogen, 15 N 15 N.
Isotopes are varieties of elements that contain differing numbers of neutrons. In this case, each of the nitrogen atoms contain seven protons and eight neutrons. This “clumped isotope” version makes up 0.0016% of abundant dinitrogen (N 2 ) gas in the atmosphere.
The work of a geochemist
Leading the research project are Jiarui Liu, who conducted the research as a postdoctoral fellow at the University of California, Santa Barbara and the University of California, Los Angeles; David Valentine, of UCSB’s Marine Science Institute; and Edward Young, of UCLA’s department of Earth, planetary and space sciences. The project includes a large team of collaborators, including Swanner. The various collaborators collected samples for clumped nitrogen measurements from lakes, aquifers, coastal basins and marine sediments.
The samples helped determine how the nitrogen isotope can be used to more precisely measure how much dinitrogen gas is formed from nitrate through the process of denitrification, a natural process caused by microbes converting nitrate into the common, atmospheric gas.
Current methods rely on indirect substitutes to determine how much dinitrogen gas is produced. The mixing of atmospheric dinitrogen can obscure how much nitrate was converted.
It’s the kind of project that fits Swanner’s expertise as a geochemist.
“Geochemists are interested in why elements are where they are and in what form they’re in,” Swanner said.
In this case, nitrogen is an important nutrient supporting the growth of aquatic plants and algae.
In Iowa, nitrogen fertilizer is applied to farm fields to feed crops. Some of that fertilizer can be lost when it leaks into nearby streams, potentially raising nitrate levels in drinking water, which can affect human health, particularly in infants and the elderly. Natural denitrification can reduce the amount of nitrate in runoff, and Swanner said better quantifying how much occurs could help fine-tune best management practices.
Measuring ‘an essential component of life’
The new method to measure nitrogen loss across various water bodies is a solution to an important problem in science, Swanner said.
“There are many ways to measure denitrification, but this clumped-isotope method seems to be able to see through other issues and arrive at a more tightly constrained estimate,” she said.
The method depends on analysis by the Panorama mass spectrometer at UCLA, a unique and powerful instrument designed to measure rare, clumped isotopes of elements. Because the instrument is so unique, widespread testing for the rare isotopes isn’t currently possible.
Prior work with the Panorama team is how Swanner’s research group connected with the project to more accurately measure nitrogen loss. A member of Swanner’s research group had been taking samples of clumped isotopes of methane for analysis by the instrument. That led to requests for samples of clumped nitrogen isotopes from Deming and Brownie lakes.
Now those samples, collected during the summer of 2025, are helping answer important questions about aquatic systems around the globe.
“Nitrogen is an essential component of life,” the researchers wrote in their Science paper, “and the balance between its sources and sinks in aquatic environments regulates ecosystem productivity, water quality, and the long-term stability of the global fixed-N (nitrogen) inventory.”
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Science
Experimental study
Not applicable
Natural 15N15N abundances constrain fixed nitrogen loss
8-Oct-2026