Wednesday, May 2, 2018

Results of our "Stoichiometry Experiment"

It's been quite a while since I've posted about our Stoichiometry Experiment. I explained a bit about that experiment in this post and this post. In this long-term experiment, we wanted to find out how soils in the McMurdo Dry Valleys will change when future climate warming creates a lot of ice melt. Along with that melted water will come a larger amount of important nutrients necessary for life: carbon, nitrogen, and phosphorus. What will the soil microbes and invertebrates do with these extra nutrients? Will the entire area of the Dry Valleys respond the same way, or does it depend on where you are in the Dry Valleys? Our goal in this experiment was to find out which of these nutrient elements might stimulate the soil organisms. Also, because different parts of the Dry Valleys might already have more nitrogen or more phosphorus in the soil than other places, we wanted to find out whether the stimulating nutrient changed from one location to another.

We did this experiment at two different places in the Dry Valleys: near Lake Fryxell and near Lake Bonney. Since the environment in both basins is so harsh for plant life, there's not a lot of carbon naturally in the soil. So, we hypothesized that both sites would be "carbon limited", meaning that if we add carbon to the soil, the soil organisms would be very excited to have the new food source and become a lot more active! Lake Fryxell and Bonney we think are both carbon limited, but we hypothesized that they would differ in whether nitrogen or phosphorus would stimulate the soil organisms. Lake Fryxell has a lot more phosphorus in the soil than Bonney, so we hypothesized that adding nitrogen would stimulate the soil biology more, because they already would have the phosphorus they need. Since Lake Bonney has more nitrogen than phosphorus, we hypothesized that adding phosphorus would stimulate the biology more, because they had the nitrogen they needed.

In the map at the upper right, the "B" marks Lake Bonney and "F" marks Lake Fryxell. The picture from Lake Fryxell shows how we added the nutrient treatments, using watering cans to sprinkle the salts dissolved in water over the plots. The cone helps prevent the wind from blowing away the water as we're pouring.
We started the experiment 10 years ago, during the 2006-2007 field season. Every year since then, we add water and nutrients to the soil. We added carbon (using a sugar called mannitol), nitrogen (using a salt, ammonium nitrate), phosphorus (using a different salt, sodium phosphate). They were added by dissolving those nutrients in water, and adding the solution to the soil. We also added carbon+nitrogen together, and carbon+phosphorus together. To make sure we weren't measuring just the effect of adding water, we had a control treatment where we only added water with nothing dissolved in it. So that gave us 7 different treatments: just carbon (C), just nitrogen (N), just phosphorus (P), carbon+nitrogen (CN), carbon+phosphorus (CP), water only (W), and a control where we didn't add anything at all (U... for "unamended"). Every year, we added these nutrients and water, and sampled the soil to see how the biology were responding. We measured respiration from the soil by measuring carbon dioxide coming out of the soil. I told you how we measured respiration on the soils back in this post. We extracted all of the nematodes, tardigrades, and rotifers living in the soil, and we measured nutrients in the soil, too.
Measuring respiration at the Lake Bonney experimental plots.

So what did we find? For 3 years, we didn't see any change in the soil at all. The biology didn't respond to the added water or nutrients. But, then, after 3 years, we started to see a difference! Soil respiration was greater in the plots where we added carbon+nitrogen. That means that the soil microbes were limited by both carbon and nitrogen, and having more of those allowed them to be more active. It just took a few years for them to be able to adjust to use the extra resources! It's also interesting, because Bonney Basin was also stimulated by carbon+nitrogen, even though it already had plenty of nitrogen (or so we thought!). We also noticed that the total number of invertebrates and total amount of microbes in the soil didn't change. Only their activity changes. It's similar to the way that having a lot of candy makes you more active and respire more, even though there's still only one of you.

h then leaves the soil. The graph on the left is for the Lake Fryxell soils, and on the right is Lake Bonney. You can see that all of the nutrient treatments are overlapping until year 3. Then, after year 3, the CN (carbon+nitrogen) treatment is higher than the others, meaning carbon and nitrogen together stimulated respiration. It's especially true in Lake Fryxell soils, but also Lake Bonney, where it was a smaller increase.

The increased activity with the nutrient additions means that future warming in the Dry Valleys that melts ice will have an impact on the soil organisms living there. But we also found that the stimulated activity was fairly short-lived, only lasting a few weeks, so it would take sustained pulses of water and nutrients to make a big impact on the soil organisms. A sustained pulse from melting ice is a likely scenario for the future of the Dry Valleys, so our experiment might tell us about the consequences of climate change for these soil organisms.

The results of this study are published in: Ball, B.A., B.J. Adams, J.E. Barrett, D.H. Wall, R.A. Virginia. 2018. Soil biological responses to C, N and P fertilization in a polar desert of Antarctica. Soil Biology & Biochemistry 122: 7-18. doi: 10.1016/j.soilbio.2018.03.025

Friday, August 19, 2016

What biome is Antarctica?

I was asked a good question by somebody through the "Ask A Biologist" website:
"What is the biome of Antarctica? Some say it is a Tundra Biome and some say it is a Desert or Ice Biome. What is the right answer?"
It's a great question, so I thought I'd put my answer here, too! (It's also on the Ask A Biologist website.)

The important thing to remember about Antarctica is that it's a big continent. It's larger than the United States, which has many different biomes! Most of Antarctica is a desert, yes. Of course, it is a very different type of desert than most people think about, because most people think of deserts as being hot places with a lot of cacti, and that's not what Antarctica looks like! So, I think a lot of people call Antarctica a tundra because they don't know that a desert could be very cold. Scientists that work in Antarctica mostly refer to the majority of the continent as being cold desert or polar desert. The difference between cold and polar desert is very technical, mainly dealing with mineral salt chemistry. Some say that the coastal soils around the bulk of the continent are polar deserts while the rest of the continent (not near the ocean) is cold desert. Some people, though, use the terms interchangeably.
McMurdo Dry Valleys: a polar desert

However, some locations in and around Antarctica have a slightly milder climate, which we call the "maritime" climate region. This includes the islands along the Antarctic Peninsula (which is the part that reaches up towards South America on the Western side of the continent), as well as the sub-Antarctic islands. Because it's less harsh, there are more plants (mostly moss and algae, but also some grass). The soils therefore have more organic matter (aka rotting dead plant stuff), making these locations more like a tundra ecosystem. However, there are no woody plants in Antarctica, and only two species of vascular plants (a grass and a pearlwort), so it is not as diverse or complex as the Arctic tundra.

King George Island: a tundra-like ecosystem on the Peninsula
So, yes, some areas of Antarctica are considered tundra (or at least tundra-like), but it's not the entire outside of the continent. Most Antarctic scientists would consider the tundra ecosystems to just be the "maritime climate" region of the Antarctic Peninsula in West Antarctica and the sub-Antarctic islands, and the rest of West and East Antarctica as polar or cold desert. And, of course, much of the desert areas are covered by ice, with less than 2% of the continent being ice-free. In my opinion, organisms still live in these regions (like bacteria), so it's still an ecosystem. Whether it's called an "ice biome" or desert probably isn't official. The ice covered regions still meet the criteria for being a desert, because while there is water, it is frozen and unavailable to biology! Precipitation is low and moisture easily lost to the atmosphere. But obviously ice is a very different habitat from soil, so it could make sense to differentiate between the two.
There's a lot of ice in Antarctica!

Wednesday, April 13, 2016

Reunited with our samples

Remember all of those boxes that we packed our frozen samples in while we were at the warehouse in Punta Arenas? They have just arrived here in Arizona.

The boxes are still frozen inside, thanks to the ice packs we put in. Once they get delivered to the lab, we unpack them quickly and load the samples into the -20°C freezer. It's pretty full!
Now that our samples are here, we can start processing them to gather the data we need to test our hypotheses!

Wednesday, March 23, 2016

Back in Punta Arenas

We are pack in Punta Arenas, Chile now. We docked about 8:00 this morning. Now that we're back in Chile, the work is not over! Today Uffe, Dave, and I spent much of our time in the warehouse packing samples for shipment home.

The samples have to stay at -20°C during the whole trip back to the U.S. We pack them in special insulated boxes with a lot of "blue ice", which are special ice packs that stay very cold. Here, Uffe and Dave are helping our lab tech Cindy pack a box of soil samples. You can see all of the blue ice that is on top. The blue ice is already -20°C, so Dave has to wear gloves to handle it.

Once the samples are packed in the boxes with the blue ice, we add a lot of labels to the outside. There are labels with the destination address, of course, but also our collection permits, information about the samples, and safety information. Plus, there are stickers telling the cargo handlers that the samples need to stay frozen and handled with care. Here, Dave is about halfway through adding labels:

We have a total of five of these boxes with our soils that need to stay frozen. We also have several more boxes that are not frozen, as well as all of our cargo. It's all packed up and ready to head back to the U.S.!

From here, our group is splitting up. Uffe is going back to Australia soon, Connor and Kelli are going back to the U.S. soon. Dave and I are staying in Chile for about another week. I will get home shortly before all of my samples do!

It has been a GREAT research trip. We got a lot done, more than we thought we would, and we worked with a lot of great people. Tonight, we all went out and celebrated a successful cruise. We ate dinner at a restaurant in Punta Arenas, which was a very welcome change compared to the food we've been eating on the ship! Unfortunately, I forgot to take a group photo...

Monday, March 21, 2016

Drake Passage, Take 2

The Drake Passage is the body of water between the southern tip of South America (called Cape Horn) and the northern tip of Antarctica (essentially, at our northern-most sampling sites). To remind you of the geography here: The southern tip of South America is a large island called Tierra del Fuego. The Strait of Magellan passes between mainland South America and Tierra del Fuego, and the very southern tip of Tierra del Fuego is called Cape Horn. So, Cape Horn is the southern-most point of South America, and the Drake Passage flows below it (between Cape Horn and the Antarctic Peninsula), connecting the Pacific and Atlantic oceans. 

The Drake Passage is named after Sir Francis Drake, a sea captain during the Elizabethan Era in the 1500s who circumnavigated the world in one journey. There are rumors that Drake discovered this passage during his journey by accident. The story is that his ships were trying to get through the Strait of Magellan (because that was the known passage between the Atlantic and Pacific), but they were blow too far south by a bad storm and discovered that the continent ended and the oceans were connected by this Passage. It’s possible that it happened this way, but some argue that it’s not likely (and there are no accurate historical accounts to prove it happened). So, naming the passage after Sir Francis Drake might be a misnomer!

The Drake Passage is famous for having very rough seas. This is because of a mixture of ocean currents and wind. The Antarctic Circumpolar Current, or ACC, is an ocean current that flows clockwise around Antarctica. Because Antarctica is a nice, round continent and there are no major chunks of land in the ocean surrounding it (just little islands), there is a clear path for the current to move in a circle around Antarctica. That makes it a very strong current, in fact the strongest one on the planet!

In the Drake Passage, the cold-water ACC meets with the warmer currents from the Atlantic and Pacific oceans. These different currents don’t mix together neatly, and the water gets famously rough here in the Drake where they come together. There are also some very strong westerly winds (that is, winds coming from the west) that make it very windy, in addition to the choppy mixing of ocean currents.

Some days are choppier and windier than other, of course. When we crossed the Drake at the beginning of our trip, the conditions were on the bad side. We had fairly large waves and very high winds (around 40 to 50 knots, sometimes even up to 60 knots). Worse conditions have certainly been reported for the Drake, but we had 2-3 days of constant wind and waves. It made for a very tough few days! This time, the weather was better. Winds were only around 30-40 knots, and while we had some big waves, it was just occasional. We didn’t have two solid days of rough seas. We fared much better this time! Last time, all of us spent most of the time laying in our bunks. This time, we were all up and moving around more, eating most of our meals like normal.

It’s hard to get a good picture to show you the waves, because you have to catch it at just the right moment. Plus, it’s hard to stand outside on deck in heavy seas! This is the best I could do. (And remember, this is from today, the much nicer trip across the Drake compared to when we were last here.)

We still have another day or two of sailing before we are back in Punta Arenas. We are just now able to see Argentina in the horizon.

(Note: Maps from Wikimedia)

Saturday, March 19, 2016

It’s not all field work…

We left Palmer yesterday morning, after picking up cargo and some passengers. We headed back up to Livingston Island, where there is a field camp at Cape Shirreff. We have to pick up some scientists who have been living and working there and take them back to Punta Arenas with us. Since the field camp is closing for the season, there was a lot of cargo to load onto the ship! We pitched in to help with the loading and unloading.

There isn’t a pier at Cape Shirreff, so everything had to ferried across on the zodiacs. First, the zodiacs carried some of us from the LMG over to the camp to help load gear into cargo bags. Uffe, Dave, and Kelli went with that group. Here’s that group waiting to get on the zodiacs and head for shore in the background:

They loaded the gear onto the zodiacs, and the MT’s were driving the zodiacs back and forth to deliver it all to the LMG. Here’s Mike and Branson bringing us a load. A crane pulls the cargo bag out of the zodiac and puts it on the back deck of the LMG.

Connor and I were on “deck duty” here on the LMG. We helped load all of that cargo into a mill van that will hold it all the way back to Punta Arenas. Here we are in the mill van, along with Cindy who also was on deck duty:

It was sweaty work! We were feeling pretty tough at the end of it:

From here, we head back to Punta Arenas. It will take a few days re-crossing the Drake Passage back to South America. The weather reports are that it won’t be too bad for the rest of today, but then a low pressure system moves in and we’ll have rough seas again. At least this time we know how to prepare. I have two water bottles full of water and a stash of apples and nuts. That way, I can just lay in my cabin without having to get up to get food and water. We’ll all hunker down again for a couple days until we arrive back in the Strait of Magellan. We’ll see if I can write any blog posts during the transit…

Thursday, March 17, 2016

Happy Saint Patrick's Day

Happy Saint Patrick's Day from Palmer Station!

We're done with field work, so we've been using our time to wrap things up in the lab. First, we had to process the samples we collected at Berthelot Island. We had help in the lab this time from Garcon, the traveling alligator. (Since he helped collect the samples, he wanted to see what we did in the lab, too.)

A while ago I told you about some of the lab work that we do. Here, Garcon is helping us weigh out the soils to extract the organisms in the soil. You've already seen the cans we use to get microarthropods like collembola and mites. That method only works well for the tiny invertebrates that live in the air around plant and soil. There are other types of invertebrates that live in the water in soil, such as nematodes and tardigrades. They rely on the water to move around, so if the soil dries out in the funnels under a light bulb, they can't move to fall into our vials of ethanol.  Instead, we have to use water to get them out of the soil. This is usually done using a setup called "Baermann funnels", but just like with everything else in the lab, we have to modify it to work on a ship on the ocean. We wrap some soil in a tissue, then put that tissue on a screen surrounded by water. The invertebrates leave the soil and float in the water outside the soil, then drop down to the bottom of the dish. After three days, we remove the soil and use a pipet to suck up the nematodes, rotifers, and tardigrades to put in vials that we send home to look at under a microscope. We were worried about the dishes of water spilling, because the ship rocks in the waves. Our MT Tom made us this great rack that's fastened to the lab bench, so we were able to run loads of samples all season!

While we're finishing in the lab, the crew are loading cargo and some people from Palmer Station are moving onto the boat to go home. We leave Palmer tomorrow morning to head north.