An Apatite for Kenyte

In previous blogs, I’ve hinted at the goals of my research, but have left a lot of questions unanswered. Why study phosphorus cycling in the first place? Where does this phosphorus come from? What guides my soil sampling when I’m in the field? I’ll try to answer many of these questions below, but please post if you’re still wondering!

One of my many sampling sites in Garwood Valley. Why did I pick this spot? What am I looking for when deciding where to sample?

All life on Earth (that we know of) depends on phosphorus and other essential nutrients. Even life in the Dry Valleys, adapted to extreme conditions and limited resources, couldn’t survive without it. Everywhere on Earth, the available phosphorus organisms can use ultimately comes from igneous rocks. Getting the phosphorus out of those igneous rocks (where it’s mostly locked up in a mineral called apatite) and into the ecosystem is a long process. Soil scientists are interested in understanding how quickly new phosphorus can enter the system. As you might expect, there are a lot of factors at play: the amount of apatite in the igneous rock, the speed at which that rock can break apart physically and chemically, the presence or absence of organisms that might help in dissolving the apatite…and we could go on.

Scientists have names for all of these factors influencing a current soil: relief, time, organisms, parent material, and climate. Each factor might be at play in determining the amount of phosphorus available in Dry Valley soils. Drawings by Ruth Heindel

In the Dry Valleys, we are in a unique position to answer questions about phosphorus cycling because of the relative simplicity of the ecosystem and some interesting differences in parent material (or type of igneous rock) and landscape age. Let’s consider parent material first. Here on Ross Island (where McMurdo Station is located), we are close to the source of some extremely unusual volcanic rocks, including kenyte. Not only is kenyte very distinct in its appearance, but it is also distinct in its composition, containing way more apatite (and thus more phosphorus) than other igneous rocks.

Two pieces of kenyte, the most distinctive rock of the Dry Valleys. These days, my eyes are trained to pick out this dark rock from far away. It’s always exciting to spot one!

Although the source of kenyte is Mt. Erebus and other nearby volcanoes, past glacial activity has scattered kenyte (and other phosphorus-rich volcanic rocks) all over the Dry Valleys in very interesting patterns. Since there is no vegetation, and kenyte is a very dark rock, these patterns are clearly visible both on the ground and from the air. Dark soils containing lots of kenyte are noticeable in Taylor, Garwood, and Miers Valleys, just to name a few.

In Taylor Valley, patterns of dark kenyte-rich soil are clearly visible from a helicopter.

Do these dark soils contain lots of phosphorus that organisms can use? Or is all that phosphorus still locked up in the rocks, unavailable to life? This season, I’m trying to answer these questions by collecting samples from the dark kenyte-rich soils to compare their phosphorus content with the amount found in the lighter kenyte-poor soils.

A large disintegrated boulder of kenyte. Does the soil under this rock contain more available phosphorus than the soil away from the rock?

But parent material isn’t the only factor that could influence phosphorus availability. The more time a soil has to develop, the more time phosphorus has to be carried away by water or wind, or taken up by an organism. Older landscapes generally have less total phosphorus than younger landscapes. Or what about the organisms living in the soils? Some microorganisms will excrete enzymes that help to break down apatite, releasing phosphorus into the ecosystem in a form that they can use. What if there are more of these organisms in one soil compared to another? This season I’m also trying to address some of these other factors. I’m collecting samples on landscapes of different ages to look at the influence of time on phosphorus availability. And I’m collecting samples for a colleague who will take a look at the apatite-dissolving enzymes in the soils to consider the influence of organisms on phosphorus availability.

The area around Hjorth Hill gave me the opportunity to sample soils of different ages. Soils higher up on Hjorth Hill are thought to be much older than the soil in the foreground.

Even in a relatively simple ecosystem like the Dry Valleys, teasing apart all of these soil forming factors is extremely complicated. While I don’t expect to solve every riddle this season, I am hoping that the boxes of samples I’ve collected so far will contain some clues into phosphorus cycling in the Dry Valleys!

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Life in the Valleys

From “Open House for Butterflies” by Ruth Kraus and Maurice Sendak

        Whether or not they intended to, perhaps the beloved Kraus and Sendak offered important scientific advice. Ground-time in the field, particularly when logistics involve helicopters transport and unpredictable weather, is truly precious. We fill pages of notebooks in anticipation of our field work– detailed schedules, lists of goals, back-up plans. Then we step off the helicopter and the proverbial timer starts. We have 1 week, or maybe 5 days, or often 4 hours to make all those plans happen. Whatever the case, it’s difficult to escape the urgent pressure to make every second count. But one of many gifts in working with a partner in the field is that we may remind each other to stop for a moment, and dedicate some time to quietly observing our incredible surroundings. In this spirit, Ruth and I designated our first task to becoming “acquainted” with the valley.

Ruth sits perched on a hilltop in the center of the expansive valley, taking it all in.

Vibrant mats appear along streams, even a shallow trickle such as this one.

As we walk around, one of the most prominent features is the myriad of twisting little streams. Some are audible if you are very quiet, though often the wind drowns that out. We stumbled across tiny ones, requiring me to squint inches away to even tell it was moving, and others that were wide enough we were unable to cross. From the helicopter they are hardly visible. Yet they create an extensive network of interconnecting waterways, like arteries, weaving in and out of ponds and feeding vital resources to a desert landscape. As we get close, colors and textures began to stand out. Along the stream edges, colorful mats, and sometimes even moss patches, grow in thick clumps.

It seems strange at first- finding red, green, and orange life forms in a desert like this. But as water penetrates the ground underneath the stream bed (called the ‘hyporheic zone’), a damp area is formed adjacent to the stream. This allows for things like algae, cyanobacteria, and microbes to be active in these wetted areas. In this way, water bodies can be extremely influential on where, when, and what types of organisms thrive in the valley.

Black and orange growth at the shoreline of a pond reveals underwater bubbles, a sure sign of physiological activity.

 

Many of these streams are currently monitored by researchers in the LTER project, where they examine flow rates, sediment discharge, water chemistry, and composition of the biological communities.

A patch of moss grows in a spot perhaps moistened by melted snow

While Ruth sampled soils throughout the valley, I’ve been focusing on the water. Water bodies here are unique for many reasons. One of which is that many of them are frozen most of the year. These harsh conditions limit the underwater community to just the hardiest species, and many cyanobacteria excel at just this. With abilities such as withstanding freeze-thaw cycles, these organisms are of particular interest to me. So while I’m here I am collecting water from lakes, ponds, and streams, and when I return to Dartmouth I will analyze these samples, including things like who’s living there, in what abundances, and their potential for toxic metabolite production.

Even under the ice, layers upon layers of leafy mats are able to scavenge enough light and thrive.

Under the water of a small pond on Hjorth Hill reveals a productive world of algal and microbial mats.

For a frozen desert landscape, it’s incredible how much life persists here. We are back in McMurdo now, but eagerly await our next adventure. Hopefully this week! Until then, thanks for your interest!

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The Thrill of New Territory

Although reacquainting myself with the familiar landscape around F6 camp was a great way to spend a few days, exploring new territory is always exhilarating. A few days ago, Jess and I were lucky enough to spend a day on the shoulder of Hjorth Hill – an area I had only explored on maps. Even my colleagues couldn’t give me much guidance – none of them had been there before either. With our maps, GPS, and sampling equipment, Jess and I headed out for an adventure.

After landing at Hjorth Hill, Jess is ready to head out on an adventure!

Why did I want to explore Hjorth Hill in the first place? I am interested in what controls the amount of phosphorus available to organisms living in soils. Previous work has identified two main possibilities: landscape age (the length of time a soil has been developing) and parent material (the rock type a soil develops from). Hjorth Hill presented the opportunity to test both of these possibilities: two different parent materials of the same age right next to the same parent material of two different ages. My hope was to be able to collect samples of all these soil types, while giving Jess the opportunity to collect water samples. Thankfully, luck was on our side!

Landing at Hjorth Hill also gave us a new perspective on familiar territory: the view back into Taylor Valley.

Our good luck started with the weather: it was clear enough to fly, but the top of Hjorth Hill was totally socked in (or, as our helicopter pilot put it, “the clouds were a bit dodgy”). This meant that instead of our original plan of landing at the top of the mountain, we had to discuss an alternate landing spot with our pilot. Once Paul learned that Jess was hoping to collect water samples, he chose the perfect location: a flat area on the shoulder of Hjorth Hill right next to numerous small meltwater ponds. Not only that, but all of the ponds hosted thick algae mats in all shapes and colors. Jess was in heaven.

The meltwater ponds were incredibly productive, with all sorts of algal mats growing along the shores.

Jess records the water temperature of one of the small meltwater ponds. Ice sits at the bottom of the pond.

Landing in unfamiliar territory is disorienting. It’s hard to match what’s on the ground with what is on a map, especially when the terrain is so bumpy. Fortunately, I had marked a few locations on my GPS before heading into the field, so we started hiking toward one of those. As we began walking, I felt confused – how would we know if we crossed over into another soil type? There didn’t seem to be much to guide us. Suddenly, however, the ground surface changed beneath our feet. Looking back, Jess and I realized that we had crossed over a moraine. We were clearly on a different parent material. Slowly, the pieces started coming together.

The ridge separating two noticeably different parent materials.

Of course, spending just one day at a site isn’t nearly enough to get to know it. I’d love to return to Hjorth Hill to spend more time exploring. But for now, we’re eager to analyze our samples to learn what Hjorth Hill has to tell us.

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