In Which...

           In Which I Introduce This Blog Post 

           So the summer researchers are steadily trickling out of Mpala, the Princeton U-Store has begun sending me emails about all of the overpriced snacks, supplies, and sweatshirts that are NOW SLIGHTLY LESS OVERPRICED FOR BACK-TO-SCHOOL, and my brother and sister have already suffered through a week of high school, which begins freakishly early in the San Francisco Unified School District. All of which means that I’m wrapping up my work at Mpala, preparing to touch down at home for a little while, and, come September, heading back east to Princeton.

            In honor of the approaching semester, I’m incorporating some actual engineering into this blog post. But don’t worry; I’m easing back into academia slowly. Stick with me through the science and I’ll show you pictures of cute baby camels, promise.

            In Which I Explain What I Did This Summer

            You’ll recall that I spent the first half of the summer hacking away at plastic buckets with Exacto knives and drills to prepare them for The Bucket Experiment.

Calibrating one of many sensors used for The Experiment

            After finally finishing setting up the experiment without major incident, I’ve spent the past five weeks running it.

            Here’s how The Bucket Experiment works. First, you spend many days oven-drying pans of soil at 105 degrees for 24 hours, or until they reach below a maximum water potential threshold (a measure of soil dryness). You spend some of the early days trying to be efficient by having pans drying simultaneously in the electric oven and the gas oven, but after setting a big plume of gas on fire and scorching your finger when you forget to put the match in before you turn the gas on, you decide that it’s best to stick to electric.

After several weeks, you’ve dried enough soil to fill all six 65-L buckets, you’ve tricked out a couple of the buckets with temperature probes and soil moisture sensors, and, after much negotiating, you’ve convinced the Kenyans at the workshop to give you enough wood to build rails for the buckets to sit on so you can fit drainage pans underneath. Congratulations! You’re ready.

Buckets, finally filled.

To begin the experiment, you saturate each of the buckets with 30 L of deionized water.

Saturating the buckets. Hydrology in the ecohydrology lab!

Over the next thirty days, you let the soil dry out while routinely taking water vapor samples from five different depths on each of the six buckets by attaching a Teflon tube to ports at each of the depths. The tube runs from the bucket ports to a Water Vapor Isotope Analyzer, which draws up the vapor and analyzes it for water content (ppm H2O) and isotopic composition of the hydrogen and oxygen in the water—that is, the ratio of heavy hydrogen (deuterium, or hydrogen with an extra neutron) to normal hydrogen, and the ratio of heavy oxygen (O¹⁸, or oxygen with two extra neutrons) to normal oxygen. You do this five times a day, at 8, 10, 12, 2, and 4. For thirty days, you live your life according to bucket time, as in:

“Are you interested in going into Nanyuki this weekend?”

“Sure! Do you think we’ll be back by 4 o’clock buckets?”

            “Are you coming to teatime today?”

            “Absolutely! I should be there just after 10 o’clock buckets.”

            And so on.

  

            The point of the experiment is to identify the characteristic isotopic ratios of water vapor at different soil depths. See, atmospheric water vapor over land comes from three sources: air currents, evapotranspiration out of plant leaves, and evaporation from the ground. The Caylor lab already has some ways to determine the isotopic ratios of water vapor brought in on air currents; in fact, that’s what Kathleen has been working on this summer. The bucket experiment is designed to figure out the isotopic ratios of the latter two sources. Water containing more light isotopes tends to evaporate directly from the top 20 cm of soil. Heavier water continues to percolate through the soil, where it gets sucked up by plant roots. So water vapor from ground evaporation tends to have a low isotopic ratio (the isotopic ratio of water stored in the first 20 cm of soil) while water vapor from evapotranspiration tends to have a high isotopic ratio (the isotopic ratio of water stored at soil depths greater than 20 cm). Once we know the characteristic ratios of all three sources, we can look at the isotopic ratio of atmospheric water vapor and by using weighted averages get a pretty good idea of how much each of the three sources contributed to the total amount of water in the air. This tells us a lot about the way water is moving through this environment, which is helpful in, say, developing more efficient water-usage programs.

            So after thirty days, I’ve taken (as I calculated in my last blog post) well over 2000 water vapor samples from soil at all different dryness levels, put them all into a giant spreadsheet, and am spending my last days here working with my supervisor, the fantastic Princeton postdoc Keir Soderberg, to turn the numbers into something useful. My understanding is that eventually our results (and my name!) will go on to a very nice looking poster 

Graph of isotope values. The poster will probably have lots of sweet figures like these on it.

          that that Keir and Professor Caylor will present at a conference in September that will hopefully lead to more interest and more grants that will one day lead to more very nice posters. Ah, academia.

In Which I Discover My Bride Price

            Having spent a good portion of this last week staring at spreadsheets and data files (as a great engineer once said: “Engineering is a lot more playing with data in spreadsheets and less playing with models and fun techy-stuff than I had expected”), I was thrilled when Saturday afternoon brought the opportunity to tag along with Thomas, one of the Kenyan researchers at Mpala, to go visit the herd of milk camels he’s studying.

            The first thing I realized when we got to the camel bomas (corrals) was that if you raise camels for commercial breeding and milk, you need a lot of camels. According to Thomas, there were nearly 200 camels at the site we visited. 

            The second thing I realized is that a lot of camels means a lot of noise: especially if 30 of them are hungry month-old camels who would much rather be eating than be visited by three mizungus. But perhaps I’ll let you come to this realization yourself.

            After we were done bothering the toddler camels, we went to go bother all of the mothers with baby camels, which were even cuter. 

Don't you think?

           This went well for a while…

            ...but the mothers soon got fed up.

            So then we went back to toddler-camel-land. While we were aggravating the mothers of the baby camels, the herders had brought the rest of the lactating mothers over to the toddler camel corral, where the herders would milk each mother before allowing her to reunite with her offspring for the night.

Yep, I milked a camel. And yep, this photo is sideways. Sorry.

            Most of the milk got stored in metal cans, but the herders reserved some for us to share with them. While we waited for the milk to boil, Thomas chatted in Swahili with the herders (translating into English for us), who seemed to be quite enjoying our company—so much so, in fact, that they began to joke about how much it would cost them to enjoy our company in perpetuity.

The eligible bachelors.

            By the time the milk was ready to drink (hot, rich, creamy, and tangy, but all in all not something I’d like to pour on my cereal), they’d come to a consensus. And while I think I’ll remain an eligible bachelorette for the time being, I am oddly pleased to report that I am worth a bride price of twenty camels. Mom, Dad, you’ve done well.

In Which I Write A Postscript

            I’m leaving Mpala Tuesday morning, but I think I’ve got one more blog post in me. I plan on saying more wonderful things about my fellow ecohydrology interns then, but in the meantime Kathleen and Alice both deserve shout-outs for their contributions to this post: Kathleen for talking over the isotope science with me, and Alice for organizing the camel expedition. Thanks, buddies!