If Device Is Right

      After spending a while learning our way around the Caylor lab and bouncing between miscellaneous short-term tasks, my two fellow Princeton interns (Princeterns?) and I were each assigned an individual project to focus on for the rest of the summer. As I have possibly mentioned before, the Caylor lab group is working on modeling the hydrologic cycle of the dry savannah ecosystem, an endeavor that requires collecting data on several different subsets of the ecosystem. So for the next two months, Alice will be collecting data on vegetation, Kathleen will be collecting data on rainfall, and I will be collecting data on soil.

     

Alice (left) and Kathleen

       One of the major components of my project involves a lab experiment designed to investigate the way water percolates through sandy savannah soil. The plan is to fill six big plastic buckets with the savannah sand, pour water into the buckets, and then use a bunch of devices and sensors to track the water as it moves through the sand and out the drainage hole.

Sophisticated science in action

       I, with help from Kathleen and Alice, had a grand old time preparing buckets for the experiment. For a couple of weeks, our lab was alive with the busy and faintly dangerous sounds of three interns enthusiastically power drilling ports for probes, Exacto-knifing chunks of rubber to appropriate sizes for drain hole plugs, and hacking away at beams of old wood to make bucket stands. Remarkably and despite my best efforts, the first-aid kit was only required twice.

       For the past ten days or so, though, there’s been an activity lull as I’ve been waiting for all of the sand for my buckets to oven-dry. Since our oven capacity is limited, since all of the sand must spend at least 24 hours oven-drying, and since I have a crapload of sand to dry, this is taking a while.

       In the interim, I’ve been trying to understand devices. Professor Caylor seems to have a bit of a penchant for devices: soil moisture probes, infiltrometers, temperature sensors, isotope analyzers, water potential sensors, and so on.

      

            

A sampling of devices. Clockwise from top left: a datalogger, a Mini Disk Infiltrometer, the WP4 Water Potential Sensor, and an EnviroSense Soil Moisture Probe

       Where he gets them all, I don’t know. I like to imagine that somewhere there exists a device-buying bazaar where scores of tenured professors congregate, wending their ways among bubbling distillation columns, piles of gleaming glassware, and the flicker of a thousand Bunsen burners to haggle with small, crafty-eyed men over the prices of Dewpoint PotentiaMeters and Ground Penetrating Radar units.

Kind of like this

       Whatever their origins, a significant number of these devices get shipped to Mpala, and many of them have never been used. My job is to follow the step-by-step instructions to put them together, Ikea-style, and figure out what the heck they do. This is where the engineering classes I’ve taken so far at Princeton are paying off. Nearly every time I open a manual for a new device, I am astounded by how complicated, tedious, and confusing the material inside appears. “This is ridiculous,” I announce to myself. “I absolutely refuse to spend hours and hours rereading the same three paragraphs to try and decipher the impossibly obtuse scratchings of this clearly illiterate engineer.” But then my Princeton engineering conditioning kicks in and I find a way to Google and Wikipedia my way through it.

Case Study: My current device, the HYPROP

The HYPROP in action. Don't be fooled by its deceptively simple appearance.

       “The intended use of the HYPROP system is the measurement and determination of water retention characteristics and unsaturated hydraulic conductivity as a function of water tension or water content in a soil sample. “

       Answer: Use this device to find out how tightly different kinds of dirt hold on to water.

       To set up the HYPROP, you first have to remove the dissolved gas from several different water samples using a system of hand-operated vacuum syringes and tubes. The water must be left to degas for a minimum of two hours, but preferably longer. The manufacturers recommend a full day. Then you have to screw the two Tensiometer shafts into the base, but do NOT touch the ceramic tips with your fingers. Or let them dry out. Or let them come into contact with non-distilled water. Also, when you’re screwing in the Tensiometers, be aware of the pressure sensor inside the base: “It is very sensitive and must never be touched! It can be destroyed even by slightest contact.” Now saturate your soil sample for a minimum of 24 hours. And then put the whole thing on a digital balance connected to a computer by a cable, but be careful, because “even a breeze can move a dangling cable causing variance in the measurement.” Finally, let the HYPROP sit for a week to take measurements until it is fully air-dried, but make sure to check the data-logging software constantly, because it tends to go buggy and suddenly stop collecting measurements.

       And then you know what you get from this whole process? One sample.

       I’m plugging through on my own, but I miss my Princeton engineering team. You know who you are.

SIDE NOTE: The secretary bird is a large, mostly terrestrial raptor endemic to sub-Saharan Africa. It is the only raptor to hunt prey on foot, which it kills either by striking with its beak or trampling with its feet. It is by far my favorite African animal, and I wanted to share the great picture I got of one a little while back: