Limnology In Action: Gas In The Water, Carbon in the Sky

All summer long, Trout Lake Station outreach assistant, Ali Branscombe will be bringing you stories from the field. Join Ali as she follows researchers slogging through wetlands, boarding boats, and wrangling fish, bringing you – Limnology in Action.

Crawford hangs the flux chamber over the water.

It is a cold morning with scattered showers and random peeks of sunshine between the dark clouds. Despite this, and a bit of hail, John Crawford and his two undergraduate assistants, Alex Johnson and Nick Jordan, work quickly to set up their equipment next to the Trout River, pulling out trash bags and plastic to cover their machines.
“Its funny, that for all the work we do in the water, how much of our equipment can’t get wet,” laughs Crawford as he hangs up a clear plastic chamber over the river’s edge, while Jordan and Johnson unpack several coolers filled with vials, tubes and measuring equipment. Within minutes their little spot by the water’s edge has been turned into a makeshift outdoor office, complete with a laptop and several processing machines. The clouds are dark and moving closer, so they set up plastic bags over as many of the electronics as they can.
“While we were doing sampling in Alaska, we had to hike miles with all of this equipment and more because we wanted to make sure we had all of the data we could possibly need; we didn’t have a chance to go back,” remembers Crawford. “Here in Wisconsin we can be much more efficient with our sampling, plus we can rely on over 10 years of flow data collection (from the University) to compare with.”
The team also collects measurements like stream width, velocity, and rate of discharge.

This is Crawford’s fourth summer working for the United States Geological Survey (USGS) studying the role that steams play in carbon cycling within ecosystems. He is a graduate student of Professor Emily Stanley at the UW-Madison Center for Limnology (CFL). This year he is stationed at the CFL’s Trout Lake Station north of Minocqua, Wisconsin. Crawford spent last summer’s field season backpacking through Alaska, conducting research in the boreal forests and alpine tundra. Over the next few years, his sampling will cover a range of ecosystems, including Alaska, Wisconsin, Colorado, Vermont, Georgia and Puerto Rico.
What people are often surprised about is what they are measuring to get their data. “We have had several people and pipeline workers approach us and ask, ‘You are looking for gas in the water?’” says Johnson.
That is absolutely true: the team’s main focus is on greenhouse gas emissions off the surface of streams. While many researchers have already studied how lakes and large rivers factor into carbon sequestration and emission, few have looked at the role of streams. Which is where Crawford comes in: studying the release of carbon dioxide and methane off the running surface water.
A carbon dioxide probe is set in the water to measure the amount of dissolved gases.

Jordan puts on hip-waders and a life-jacket to enter the stream while Johnson takes his position at the computer. Crawford sets a long instrument in the water that looks like a poorly-made flute. It is a CO2 probe that has been modified to be used under water. Inside the plastic tube is a membrane that is only permeable by gases, measuring the amount of CO2 dissolved in the water rushing through the tubing. Dangling above is the “flux chamber” –  a plastic polygonal chamber that rests just on the surface of the stream and creates a seal. The air inside the chamber is measured by an infrared gas analyzer, a machine that reads the gas concentration in the chamber. Running these readings into the computer, a computer program (written by Crawford) measures the change of gas concentrations in the chamber, thus revealing whether the stream is giving off or capturing carbon. More often than not, it is releasing consistent quantities that initially seem minute, however, looking at the big picture is a very different story.
For example, if one square meter of forest takes up 100 grams of carbon every year while one square meter of stream releases 5 grams of carbon per day, it seems like the stream doesn’t have much of an impact. But over time the carbon released by the stream soon outnumbers the forest’s contribution to the atmosphere.
Crawford and Jordan take water samples.

“Streams are really good at exchanging gas,” says Crawford. “If this whole area of forest was the surface area of a stream, it would be releasing incredible amounts of carbon into the atmosphere.” So while streams do not make up a significant portion of surface area around the globe (barely even a single percent in the northern U.S. proportionally to other landscapes), they can still be significant as a source for carbon emissions. “What we are trying to do is get a handle on how many streams there are, and to see if there are ‘types’ that can be identified in given conditions.”
Working in Wisconsin, Crawford has the opportunity to evaluate his sampling with large-scale data that has been collected in Wisconsin though USGS, UW-Madison, and NOSAMS. “The great thing about having years of data on stream discharge is that we can look at the influence discrete events, like rain or flooding, versus large scale events like droughts;” all of which can have influences on carbon cycling.
Johnson records data from the Infrared Gas Analyzer and watches the laptop quality check the data

From the infrared analyzer, Johnson enters his CO2 readings into the computer. Within a few minutes, line graphs pop up, providing instant feedback and quality checks of the data.
As Crawford and his crew continue collecting and assembling data, more and more insights will be found about the connections landscape and hydrology have to the carbon cycle. “A stream-network is like a tree,” Crawford says, spreading his fingers out and making branches and a trunk with his hands. “You have the Mississippi, for example, as the trunk, and all of its tributaries above that. Above those, the smaller branches, are what we call headwater streams. When you add them all up, they can become a significant proportion to the ‘tree.’” He relaxes his hands and looks off. “And if you think about it, its these headwater streams that are the most connected to the terrestrial landscape.”
John points out significant recordings on the laptop. Analyzing data can be done instantaneously in the field, thanks to John’s program.

Jordan and Johnson start packing up. In about 10 minutes all the equipment is in the truck. The team takes a few minutes to shake off their wet clothes, then they climb in – ready to do it all over again tomorrow.
All pictures courtesy of Alexandra Branscombe

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