After each of us had walked up and down the stream, the lead researchers met up and settled on the experimental reach. This was a 300-yard long stretch of stream surrounded by jungle with no major side channels and a variety of pools and shallow areas (riffles) characteristic of the stream. Most streams naturally sort themselves into a series of pools and riffles through the natural processes of erosion. These processes also lead to the typical meanders or “S” shaped bends that characterize flowing waters.
We picked out sampling sites from the top down, each one a bit farther apart from the next, so we could sample correctly. Once the experimental area was set, we worked with Edgardo and the other Panamanian helpers and found the best way to get from each sampling site along the stream to the next. They then used their machetes (a standard item of hiking and work equipment for most rural Panamanians) to clear a rough path. We marked each of the sampling sites along the stream with fluorescent tape, and set up our equipment for the initial measurements.
The trail had its hazards. We could not step in the stream while the experiment was going on, so needed to have minimal crossings and placed logs and rocks to get across where we did need to go. The trail wound its way through a bit of sparse jungle, but the animal trials made false leads and it was easy to wander off the wrong part and we had to pay careful attention. I hoped we would not be caught on the trail after dark. After the sparse jungle the trail went across a marsh, which we filled with logs, but they kept sinking as we would walk across them and the crossing was precarious at best. Right on the edge was a palm tree, and it was natural to grab the tree if you slipped into the mud off the logs. Unfortunately the tree had huge spines and the spines had an irritating substance on them. More than one of us grabbed the tree by mistake and was impaled. It is the kind of mistake you only make once; unfortunately I made that mistake several times.
The trail went next to the stream in parts and up and down steep-slippery sections, and included some logs. At the top of the trial was a large rock bar where we were setting up our system to add the chemicals to the stream. Just above this part there was a branch in the stream and the jungle was a bit more open, so large shafts of sunlight played through the branches onto the stream. This was a beautiful spot where we could see a slope too steep to climb rising between the two stream branches and huge trees towering hundreds of feet above our heads up the slope. Boulders the size of shuttle busses had fallen off the sides of the steep slope and lodged in the stream channel, and massive tree trunks had recently fallen across the stream above taking out many others on their way down. Above our top location, the stream was a jumbled mass, and it was very difficult to get through to the stream above, but the effect was wonderful.
Since we were going to use an inert chemical tracer to follow how nitrogen moved into the animals in the stream, samples needed to be collected to establish a baseline, and also to establish our basic protocols of measurement. Our group split into smaller groups.
One group collected the leaves and algae in the stream that form the base food source for all the animals in the stream. These samples were collected from a known area so we could estimate the relative amount of each that were present in the stream. At previous streams where the frogs had gone extinct the algae had exploded, so we wanted to catch that with detailed measurement. Even in these shaded streams there was enough light to allow some algae to grow.
Other groups collected the tadpoles, insect larvae, crabs, fishes and shrimps that populate the stream. These collections required careful netting and counting of individuals. We needed to be absolutely certain to quantify the existing conditions, because we knew of the changes that were coming and there was no going back. All these collections also needed to be made with much caution to minimize the disturbance of the stream channel so as not to interfere with our measurements in the following days.
Simultaneously, Bob, Alex, Matt and I set about making additional basic preliminary measurements required to start the experiments. Measurements were made with chemical sensors (measuring oxygen gas dissolved in the stream water, temperature, and other important water quality parameters). We started electrodes that would record the chemical conditions and temperature in the stream for the entire duration of the experiment. We took chemical samples required to calculate how to start the experiment the next day.
We started other measurements to determine how the stream responded to pulses of nitrogen and how pulses of tracers we released at the top moved down the stream. The results from these releases allowed us to account for how quickly the water moved through the system, and how much water was flowing. We took background samples of water to measure nitrogen so we could calculate how much nitrogen tracer to add and for how long. All these water samples would be analyzed later that same evening. Bob had a very nice approach where we could add the chemicals streamside and the samples would incubate and be ready to analyze that evening. Length, width and depth of every few feet of stream over the 300 yards or more of the experimental reach needed to be recorded.
Some time was spent just sitting on the stream bank and waiting between measurements, occasionally writing down numbers in the field book. Field research can be a curious mix of rapid, hard, physical work, then intense calculation and concentration, interspersed with waiting and observing.
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