It’s been a long time since we’ve updated, but we’ve been very busy. After having isolated sampling dates where we were able to get into the Dry Valleys for the first few weeks, we finally ran into two solid weeks of great weather. Today we’ll talk about the experiments we maintained and sampled, what we do with the samples once we get them back into the lab, what sorts of animals we’re looking for in the soil and the trip Diana, Uffe, Byron and Ian took to the Beardmore Glacier.

Our experiments for the Long Term Ecological Research (LTER) work we do here are spread out along the south sides of three lakes in the Taylor Valley. From east (on the right, closest to the Ross Sea) to west (on the left, closest to the polar plateau) the lakes are Lake Fryxell (with F6 camp), Lake Hoare and Lake Bonney.

Over the last week and a half we’ve been to each of our sites at these three lakes and sampled from and then treated another of our long-term experiments, the Biotic Effects Experiment. This experiment has four treatments: added water, increased temperature (about 2 degrees Celsius), increased temperature and added water and a control (which if you remember from our discussion of the stoichiometry experiment is there to provide us with baseline data without the influence of the treatment manipulations).

Adding water is pretty straightforward. Much like the stoichiometry experiment, we added 5.6 liters of water to each plot that was supposed to be watered. We did this with the jugs and watering spouts we used in the stoichiometry experiment. Temperature is also pretty straightforward, and to raise the temperature of the plots we let the sun do the work. The cones we use to outline where we need to water in the Biotic Effects and Stoichiometry experiments are actually used for the temperature treatment. They’re made of nearly-clear fiberglass that helps to trap heat from the sun in the area beneath the cone, and in this way we can leave the cones tightly strapped down to stakes on the plots year-round and let the sun do all of the work for us. You can see the cones placed on the sites below.

With this experiment, we can see what the effects of changes in climate might be on the soil animals in the dry valleys. If the dry valleys get warmer and wetter, our experiment will help to predict in what ways the soil animals will respond. The design also allows us to see how each of these climate variables may affect the soil animals alone, without the influence of the other variable. This means we can also say what proportion of the change we see due to increased temperature and precipitation may be due to the effects of the increased temperature by itself, or the extra water.

While we were out at Lake Bonney, we also set up another experiment that we plan on monitoring for many years to come. Last year this area where our experiments are located got very wet when an increase in streamflow resulted in a large patch of moving water and seeps. We had the boundary of the wet area marked out last year, and this year we were able to put in spikes with copper tags to indicate areas we wanted to sample from over the next several years. Additionally, we also ran three lines (transects) that extended from the areas that had been dry throughout last year through the area that had become flooded and then back out again into dry soil. Each of these transects was located roughly parallel to the others, with one toward the base of the slope our experiments are located on, another halfway up the slope, and a third quite far up the slope. Once we had these sampling locations marked out, we took our first batch of samples, as you can see here with Uffe happily getting some soil for us:

When we sample soil, we do two things. First, we scrape off the very top layer of soil in order to see how much photosynthetic activity the algae that live in this area are undergoing, and then we try to collect the top 10 centimeters in the small area directly under where we sampled the algae. This soil is put into bags labeled with the experiment we’re conducting as well as the particular site or plot the sample came from so that we know the origin of each sample. We then take the bags back to the laboratory and there we extract the animals and measure the moisture of the soil.

Measuring soil moisture is very simple. First we weigh small cans and write down their weights. We then add 50 grams of soil into each can and note the number of the can and which soil sample was added into it. Finally we place the soil cans into an oven at 105 degrees Celsius for a day, which causes all of the water in the soil to boil off and leaves only the dried soil. Once these dried soils are weighed, we can subtract the weight of the can itself and then calculate the difference between the wet and dry soils and then determine what percentage of the wet soil was water.

The process to extract soil animals is much more involved, and we usually have three people performing various steps at the same time. The first step is done while we’re weighing out soil for soil moisture: once the soil for soil moisture has been measured out into a soil can, the person working at the balance also measures out 100 grams of soil for extracting the animals. We do this in a special “laminar flow hood” that helps to filter the air blown over the samples in order to minimize contamination–nematodes are everywhere, and we want to try and extract only the nematodes that are in the soils we have collected. This 100 grams of soil is then placed into a small beaker that is half-filled with water. The soil is then mixed up in the water to make a sort of soup. All of the heavy particles such as rocks and bits of sand fall back down to the bottom of the beaker while the lighter particles float around in the water. These lighter particles include small soil particles, but more importantly they also include the nematodes and other soil animals that we’re interested in collecting.

This soil and water mixture is then poured over a series of sieves and sifted out so that only the very small particles are captured and transfered into a centrifuge tube. We then spin the tubes in a centrifuge very quickly for 5 minutes in order to push all of the animals down to the bottom of the tube. After the 5 minutes is up, we pour out the extra water on top (being careful to keep some of the water that might have animals in it) and then add in the magic ingredient: sugar water. Once we add the sugar water, we mix it up with the soil in the centrifuge tube, which tosses the soil animals back up to the top of the water column. This time we centrifuge the tube for only one minute, and then take it out. All of the soil gets tossed to the bottom of the tube but all the animals stay in the water because the sugar keeps them afloat. We then pour the water out over a very fine mesh screen and then rinse the screen into a clean tube, and voila! We have a small sample of water that contains the animals from all the soil we started with.

Here’s Bishwo pouring the soil-water mixture over a set of sieves before the first centrifuge run.

Here is Bishwo rinsing a sieve with Zach weighing soils behind him.

And here is Uffe waiting for the centrifuge to finish up.

When we look at the animals under the microscope, we identify the nematodes to species and then further break them down into the number of males, females and juveniles and how many are alive and dead. We also count other organisms such as mites, tardigrades or rotifers, and you can see some images and movies of these animals here. First you’ll see a tardigrade (or “water bear”) followed by a nematode. Later on, 1:05 in, a rotifer appears. This video gives a good idea of what it’s like to look through soil samples!

Earlier this week Diana, Uffe, Byron and Ian (from the University of Waikato in New Zealand) got a chance to start sampling for another of the grants we have going. Early Tuesday morning they got onto a small “twin otter” plane and flew from the ice shelf outside of McMurdo down to the Beardmore Glacier. This glacier is very far south, and rises from the ice shelf up to the polar plateau–this is the same glacier that Shackleton and Scott used to get up to the plateau and eventually (for Scott) to the south pole. Here they landed near Mount Kyffin, which is mostly covered by snow except for a few areas that have exposed soil. They climbed across the ice and snow over to these exposed areas and collected samples to examine back in the lab.

Here they are back at the plane before heading back to the lab. From left to right: Uffe, Ian, Diana, Paul (their mountaineer) and Byron:

With these samples, they are looking to see what animals are found on the exposed rock surfaces that act like islands amidst the glacier and snowcover. They’ll take the animals they find and sequence their DNA, and then check to see if the populations of animals they collect have diverged through time and if so try to estimate how much time has passed since the populations were together. They can then compare these estimates with the age of the surface of the soil they collected the animals from and determine whether the animals are newer arrivals or whether they’ve been there since the time the soil patches were isolated from each other. Neat stuff!