The art of researching alpine CO2 emissions

Network News Spring 2014, Vol. 27 No. 1
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How did a Liberal Arts major from Vassar College end up researching carbon respiration in gale-force winds at the height of winter in the Rockies? Doctoral candidate John Knowles just smiles and shakes his head, recalling the story. 

After graduation, Knowles found himself "under-stimulated" at a ski-resort job in Vermont. Web-surfing one day, the topic of hydrology caught his eye. Through a friend, he was advised to contact Mark Williams and other researchers at NWT. 

"I don't think any of them returned my first emails," Knowles recalled, rolling his eyes. Perseverance led to another let-down when Williams informed Knowles that he was "too green" and needed field experience before anyone would take him seriously as an applicant for grad school.

It's a good thing Knowles didn't give up. Today, his studies address one of the most alarming positive-feedback loops in climate-change research: the release of carbon dioxide (CO2) from warming tundra soils. 

Knowles' research is differentiated by his focus on alpine tundra. He constructs novel devices that capture the CO2 rising from alpine soils to measure effects of season and soil moisture on carbon respiration. 

"Forests usually absorb CO2 from the atmosphere," Knowles says, "But we now know that arctic tundra can pump a lot of CO2 into the air as the permafrost melts. We need to know if alpine tundra is doing the same thing. Arctic and alpine soils experience different meteorological conditions, so they might respond differently to climate change."

Knowles finally attracted serious attention from Williams and from his current advisor, Peter Blanken, after gaining some experience as a field assistant studying stream channels for flood prediction, and after taking classes in hydrology and geomorphology through the Continuing Education program at the University of Colorado-Boulder.


Blanken and his colleagues were about to begin a study of carbon respiration involving the construction of eddy flux towers to monitor the flux of CO2 and water between the soil and the atmosphere. Knowles was chosen as the right student for the job. "I was there on the first day of construction in February 2007.  It was an extremely windy day in the alpine tundra," Knowles related with a look suggesting understatement. Winds on Niwot Ridge commonly exceed 100 km/hr. 

Knowles and his advisor used the first two years of eddy flux data to show something previously unobserved: alpine tundra on Niwot was losing CO2 each year (Blanken et al. 2009).  The rate of carbon respiration they reported was striking, especially because permafrost is less extensive in alpine than in arctic regions, and because little is known about how rapidly alpine permafrost is melting.  Later, Knowles also found that there was more sublimation (evaporation) of snow from areas where wind scoured the ground than where snow persisted (Knowles et al. 2012).  "Airborne snow sublimates at a higher rate," he said. 

Knowledge about spatial variation in rates of sublimation got Knowles interested in the potential for similar variation in CO2 emissions.  He decided to focus on how soil moisture might affect carbon respiration.To capture respiration along a gradient of dry to wet alpine tundra soils, he has created two types of sampling devices.  His first chamber design gathered useful data in all but the coldest months.  His new design employs a 15 cm long stainless steel tube, or gas well, inserted into the soil and capped by an evacuated canister that "pulls" respired products from the soil.  "The gas wells work pretty well all year," he said.

What Knowles has found is that "wet spots" in the tundra contribute disproportionately to carbon respiration on Niwot Ridge.  Noting that other researchers have confirmed several patches of permafrost on Niwot Ridge, he said, "It's plausible that there is permafrost associated with my wetter sampling sites."

Knowles is interested in both the rate and the date of carbon respired.  "[Radiocarbon dating techniques] show that carbon respired during the summer is generally modern, less than five years old, but carbon respired during the winter can be up to ninety years old," Knowles said, adding that wet spots on Niwot Ridge are similar to peat, which often contains a lot of old carbon.  This old carbon would represent an unaccounted-for source of carbon being added to the atmosphere.  “We need to measure the amount of soil carbon at these locations, to see how much CO2 they could contribute to the atmosphere," he said.

In the final phase of his dissertation research, Knowles is busy quantifying and dating carbon from organic and mineral components of the soils at his sampling sites.  These data will help him construct a "mixing model" to better understand the origin of carbon sources that contribute to each sample he collects. He is also working on a paper that reviews research that has been conducted using eddy flux data at NWT.

Explaining the relevance of his work, Knowles displays an ease with language that hints to his Liberal Arts background.  "Soils contain the largest reservoir of carbon in the terrestrial biosphere, so if we liberate even a small percentage of soil carbon, we could greatly increase the amount of CO2 in the atmosphere." 

Further reading

Blanken PD, Williams MW, Burns SP, Monson RK, Knowles J, Chowanski K, Ackerman T. 2009. A comparison of water and carbon dioxide exchange at a windy alpine tundra and subalpine forest site near Niwot Ridge, Colorado. Biogeochemistry 95: 61–76.

Knowles JF, Blanken PD, Williams MW, Chowanski KM. 2012. Energy and surface moisture seasonally limit evaporation and sublimation from snow-free alpine tundra. Agricultural and Forest Meteorology 157: 106–115.