Friday, June 26, 2009

Who am I and what is ARCSS/TK?

Before explaining more about this project I should say a bit about who I am. My name is Breck Bowden and I'm a professor in the Rubenstein School of Environment and Natural Resources at the University of Vermont in Burlington Vermont. I teach courses in watershed science and planning. And I do research on interactions between landscapes and streams. Some of the landscapes I study are developed and there are immediate applications for the research I do. For example some of the research I do in Vermont is used to inform policy and management decisions about stormwater management. In Alaska, I study relatively pristine and undeveloped landscapes. Though the influences of people are evident directly and undirectly here. If you want to know more about me you can go to my website. But this blog is not primarily intended to be about me.

Instead, this blog is mainly about the "ARCSS/TK" project. ARCSS is an acronym for the Arctic Systems Science Program that is sponsored by the US National Science Foundation. The mission of ARCSS is to fund leading edge research on how changes in the arctic system will affect the future, not just of the arctic but of the global system. We refer to our project as the ARCSS/TK project because ARCSS has funded us to study a particular phenomenon of the arctic system - thermokarst - the "TK" in our name.

To understand why we are interesting in thermokarst features you need to remember that the arctic is so cold that most of the soil remains frozen all year long, even during the summer. This is the so called permafrost; permanently frozen soil. A thin layer of soil on the top will thaw each year - the active layer- allowing tundra plants to root and grow. But below the active layer the soil remains frozen solidly all year. For the most part the frozen soil looks and feels like brown concrete. Occasionally, however, there are large inclusions of nearly pure ice, which arise for a variety of reasons. Some of this ice is leftover chunks of retreating glaciers from the last ice age that have never melted! In other cases water creeps into cracks and crevices in the soils and forms layers and wedges of ice than can grow and persist for decades, centuries, and perhaps longer.

As you might imagine, the frozen soil is hard. But if the permafrost warms and thaws, the once-frozen soil loses internal structure and can subside unevenly under its own mass. This phenomenon is called thermokarst. The word karst refers generally to “uneven ground” and with the suffix thermo- literally refers to ground that has become uneven due to thermal changes. The formation of thermokarst is a natural phenomenon, but the long-term and large-scale consequences of thermokarst on the arctic landscape are poorly understood. In some settings the formation of thermokarst can lead to some fairly spectacular results. The “drunken forests” of some boreal areas is one example that has received attention recently
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Less well known impacts include a variety of types of hillslope failures - land slides - that can follow thermokarst formation. Formation of thermokarst first destabilizes the soil. Subsequently, an event like a large or persistent rainfall event may initiate mass movement of the soil downslope in what we have termed a thermokarst failure. These failures can take a number of different forms, but in all forms these thermokarst failures have the potential to cause important changes to the land surface.

For example, thermokarst failures expose large areas of fresh mineral soil that were once covered by tundra vegetation. Surprisingly little is known about the successional sequence of vegetation in this new primary habitat. One possibility is that these areas are ultimately ideal habitat for shrubs, where previously the habitat may have been grasses and forbs. Shrubs have a number of different and interesting impacts on the arctic landscape. Shrubs are excellent browse for moose, which were once rare in arctic Alaska but have become increasing common. Shrubs also tend too hold and collect snow in the winter and consequently insulate the soil around them, which may maintains microbial processing rates in the soil for longer periods and higher rates than would have been the case in the past. This could have important impacts on carbon and nutrient processing in arctic soils.

Thermokarst failures may directly affect microbial processes as well. During the warmer months these disturbed areas may become hot-spots of microbial activity. There is good evidence that permafrost soils contain vast quantities of carbon that if disturbed, can be used by microbes. Thermokarst failures may be particularly strong sources of radiatively-active trace gases, most notably methane but also carbon dioxide. Methane is many times stronger than carbon dioxide as a greenhouse gas and so even relatively small emissions of methane to the atmosphere may be more important than relatively larger emissions of carbon dioxide.

Finally, thermokarst failures move tons of soil across the landscape, as well as the carbon, nitrogen, and phosphorus associated with that displaced soil. At the very least, these events are responsible for reshaping the local landscape. But when these thermokarst failures happen to intersect lakes and rivers, as they often do, they can inject massive quantities of sediment and nutrients directly into these waterbodies, which may be subsequently transported downstream. In addition, the injected sediments and nutrients may alter the community structure and ecological function of the lakes and rivers, themselves, in ways that we have not yet quantified.

In summary, thermokarst and thermokarst failures have the potential to substantially alter the arctic landscape. It is important to recognize that the formation of thermokarst is a natural phenomenon. However, we now have strong evidence that the rate of thermokarst formation has accelerated in the region of Toolik Lake in recent decades, presumably in response to climate warming in the arctic. Taken individually a particular thermokarst feature is perhaps merely an interesting oddity. However, taking a longer temporal and larger spatial perspective, it is reasonable to conclude that thermokarst formation has important impacts on the structure and function of the arctic landscape. If the rate of thermokarst formation increases, then it is possible that important aspects of the structure and function of the arctic landscape will change rapidly as well. It is important that we understand these interacting process to better understand how climate change will affect the arctic environment in the future.

In future posts I'll tell you a bit more about our project and various things we are doing.

Cheers. Breck


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