Thursday, December 27, 2012

Sampling water tracks

We are now at Lake Hoare camp sampling water tracks.

My role is to measure soil respiration on the water tracks. That means I'm measuring how much carbon dioxide (CO2) is coming from the soil. That CO2 comes from the respiration of all the microorganisms living in the soil: the bacteria, fungi, nematodes, rotifers, and other tiny creatures that breath in oxygen and breath out CO2 (just like we do!). By measuring how much CO2 they're producing, I am estimating how much biological activity there is in the soil. We want to know if there's more or less activity in the water track than there is outside the water track.

To measure respiration, I use an "infrared gas analyzer". It's a fancy machine that measures the concentration of CO2 in the air above the soil. Here it is:
The white chamber (that looks kind of like a lantern) nests over the soil. It carefully sucks up the air coming from the soil and pumps it to the yellow box, which contains the analyzer. The analyzer shoots an infrared beam through the gas sample. CO2 absorbs infrared energy (which is why it's a greenhouse gas), so the amount of infrared energy that makes it all the way through the gas sample tells us how much CO2 is in the gas. The computer in the analyzer takes that information and calculates a respiration rate using a lot of math equations that describe the physics of CO2 and gas. All of the data gets stored by the analyzer, which I later download to my computer.

While I was measuring CO2, Lily was running ahead of me measuring soil moisture at each site. She used a probe to do that, which is what you see in the picture above. The probe shoots out a gentle electrical pulse, and measures how long it takes to get the pulse back. Water conducts electricity, so the higher the voltage that returns, the wetter the soil is.

After taking respiration and moisture measurements along the water track, I take a soil sample from the each location. We use a trowel to scoop the soil into a plastic bag. That bag will get packaged, frozen, and shipped back to Arizona State University for more measurements.

I will measure the biomass of critters in the soil that are doing the respiring. That will tell me how many organisms are producing the measured amount of CO2. I'll also measure other properties of the soil that influence the movement of CO2, such as soil texture and water content.

Yesterday, Lily and I sampled one water track on the north shore of Lake Hoare. Today, Joe and I will fly across to the south shore to sample another. It's great being able to finally get our work done!

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