Nitrous Oxide Sampling: a tale of jerry-rigged restaurant pans

Last trip down I wrote a post about the adventures Paul and I had jerry rigging restaurant steam pans into fancy-pants, high-functioning gas sampling chambers. Now that I’m back in Brazil and have official permission from the landowners at the farm to begin this project, I’ve been out in the field a few days a week sampling for atmospheric nitrogen losses!

Brief summary of my research focus down here: the big question here is, after deforestation for Amazonian agriculture, does the way nitrogen moves around the system change? If so, how? And, more particularly, does it change how much nitrogen is emitted as nitrous oxide (N2O), a powerful greenhouse gas?

Measuring N2O losses (that is, measuring emissions of this particular greenhouse gas) goes down kind of exactly as you’d expect it to. Here’s the nitty gritty, complete with fun photos!

First, we roll up to a site in a sweet IPAM truck. My sites are either primary Amazon forest, soybean agricultural fields, or soybean agricultural fields that are planted with corn in the off-season to get the farm some extra dough. Here’s a photo of one of the forest sites. You can see a gas sampling chamber in the background. It’s the shiny silver thing.

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We tromp out to wherever we’re set to be sampling that day (modern GPS resources are amazing!) and put out restaurant pans that are cut open at the bottom in order to be driven into the soil. Then get ready for some high tech solutions… we take a piece of wood, put it on top of the thingy, and jump on it until the thingy is driven into the ground. Yes! Science!

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After waiting a respectful amount of time for things to equilibrate, we get ready to start gas sampling. Here a second restaurant pan comes into play. For each “base” (thingy driven into the soil), I set up a second pan that is insulated, airtight, and has a sampling port in the top. We start a timer, and fasten the top to the bottom. What’s left is a little patch of soil that is emitting gases that are getting trapped inside of these chambers.

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Now the air in this chamber is building up with gases over time. To measure the emissions rate (i.e. N2O emissions over time), I sample the gas inside at minute 0, minute 10, minute 20, and minute 30. Then, we’ll use those four time points to say what the N2O emissions rate was for each little patch of soil. Sampling the gas is pretty rad. I take a syringe, stick it in the sampling port, suck out some air, and then put that air into air-tight glass vials. Those vials will come back to the States with me and get measured in comparison to known N2O gas mixes. Fancy stuff!

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Since I have 5 chambers at each site each time I sample, and they all need to be sampled at minute 0, 10, 20 and 30, we have a pretty streamlined set up in which every 2 minutes we move from one chamber to the next to sample. It’s pretty awesome (in the forest) and sometimes boring (in the corn) and sometimes terrible (in the soybeans). The forest is dope and there are tons of birds and cool plants. The corn I get a crazy rash on my arms every time (from being cut up by the rough corn leaves?) and the soybean fields are TERRIBLE this time of year. There’s no soy down right now, so it’s basically a bare field in the baking sun with a million biting insects everywhere and landing on your face for 75 minutes. WHY WOULD YOU BITE ME ON MY FACE???

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At the end of the gas sampling, we take a bunch of soil samples to test for like five different things, and then we roll on to the next location. Huzzah!

I have two experiments going: one looking at temporally fine-scale changes in emissions in response to “events” (rainfall, agricultural management activities), and for that I go to a subset of my sites twice a week or once a week for a bunch of weeks in a row to have some data over time and watch it for small fluctuations in response to things we hypothesize about (rainfall, agricultural management activities). The other experiment is I go to a bunch of sites only a few times over the year in order to get a more broad-scale estimate of how much N2O this landscape emits on an annual basis. In short: Q1 – what events disrupt nitrogen in this system and how? Q2 – if we want to scale up N2O emissions, approximately what annual emissions rates are associated with different land uses?

Finally, I’d be remiss if I didn’t mention the awesome folks that I work with down here. The IPAM field team is INCREDIBLE. It’s a bit of a field ecology cliche, but it’s very true in my experience: field teams tend to be uniformly more thoughtful about the system you’re working in, more knowledgeable about the specifics of it, better versed in the species present, and generally more capable human beings than I am, have been, or ever will be. I could not do even one bit of what I’m doing without these guys and, to a man, I adore them. Plus, they teach me Portuguese while we’re waiting two minutes to sample the next restaurant pan. Most importantly, they make sure that, as an oblivious foreigner, I don’t get eaten by snakes in the forest.

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2 thoughts on “Nitrous Oxide Sampling: a tale of jerry-rigged restaurant pans

  1. Hahahah! So “….they make sure that, as an oblivious foreigner, I don’t get eaten by snakes in the forest.”
    These snakes are so intense in the Amazon that they don’t just bite you… they eat you!!

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