Deep in the Northern Wisconsin Peat (with video)

How will ecosystems respond to ongoing and future climate change?   Will changes in ecological communities track temperature and precipitation in a linear fashion?  Or will abrupt changes occur when particular climatic thresholds are crossed?  What sorts of information might help us better anticipate future ecological change?

After a sweltering week of fieldwork, these questions seem quite timely….

A portion of a sediment core from the Triangle Lake bog mat in northern Wisconsin. This drive captures the organic-rich sediments at the very bottom of the basin, which accumulated  when the lake first formed, likely over 10,000 years ago.

Ecosystem state shifts and long-term perspectives.  The possibility of rapid transformation of ecosystems in response to climate change is of great concern to ecologists and land managers.  Abrupt and dramatic changes in the composition and functioning of ecosystems, commonly referred to as “state-shifts,” have occurred in the past, and may be triggered by climate-induced disturbance events, such as fires or droughts.  However, the past century of climate and ecological changes provide only a few examples of such events, and lack long-term perspectives on their effects.  Paleoenvironmental records provide long-term perspectives on both climate and ecosystem dynamics, and are therefore well suited for studies of climate-ecosystem relationships.

Google Earth image of northern Wisconsin showing the abundance of kettlehole ecosystems in the region.

The Northern Wisconsin Landscape.  Northern Wisconsin is a land of lakes…and peat-accumulating wetlands (i.e., peatlands).  When the glaciers retreated from this region, they left behind blocks of ice.  These ice blocks melted and the depressions that were left on the landscape became the region’s many lakes and wetlands.  These basins are commonly referred to as kettles or kettleholes, and are often occupied by lakes or peatlands  – and in many cases contain some combination of both.  Commonly, kettle lakes are bordered by a peatland that floats on a trapped water layer.  When you walk on these peat mats, it feels like you are walking on a waterbed.  “Quaking bogs,” “floating bogs,” and “schwingmoors,” are just some of the names used to refer to these unusual ecosystems.

Kettlehole ecosystems and paleoecology.  Kettlehole ecosystems provide a range of benefits (i.e., ecosystem services), including habitat for biodiversity, groundwater recharge, sites of carbon storage, and areas for recreation.  In addition, these systems have tremendous scientific value, particularly for the study of past ecosystem responses to climate variability, because they leave a detailed record of their own development in the form of peat and lake sediments.  By collecting and examining sediment cores from these systems, much can be learned about how they have changed in response to past climate changes.

Triangle Lake in northern Wisconsin. The bog mat along the edge is dominated by Sphagnum mosses and leatherleaf (Chamaedaphne calyculata).

Recent research has demonstrated that extreme drought and water-level fluctuations probably trigger the initiation and expansion of peatland in kettlehole ecosystems (see related paper), effectively transforming the ecosystem from an open lake to a peatland (with or without a central lake).  This transformation likely occurs quite rapidly (i.e., likely within a decade or so) and would be expected to cause abrupt changes in ecological communities and processes.  For example, peatland establishment along the margin of lakes leads to changes in lake-water chemistry (e.g., higher acidity, higher dissolved organic carbon) and lakes with and without peat mats are characterized by very different aquatic communities and food-web structure.  In fact, lakes with extensive peatland can become too acid to support fish populations.  Furthermore, the transformation of kettle lake systems into peat-accumulating wetlands results in dramatic changes in biogeochemical processes, particularly rates of carbon storage.

We are investigating these ideas further by examining the history of peatland development in kettlehole ecosystems along a landscape gradient in northern Wisconsin.  Our research aims to provide a long-term perspectives on the role of hydroclimate variability in triggering abrupt and permanent state shifts in ecosystems, as well as to better understand and characterize the immediate and long-term ecological consequences of these events.  Such threshold responses are difficult to anticipate, and our results will hopefully provide a foundation for evaluating the relative sensitivity and vulnerability of ecological systems.

“Wading through the slimy ooze

You can drive away your blues

Romping through the swamp”

– Peter Stampel-

Alex Ireland measuring the depth of the basin with a probe rod.

Two weeks of fieldwork in late June and early July.    Nice work if you can get it?  Not really.  By the third day, we were almost drained of our life force by wood ticks and deer ticks (the ones that carry Lyme disease). What little blood remained in our bodies nearly boiled in the brutally hot temperatures that followed for the remainder of the work.  However, we did manage to make a great deal of progress.  The field crew included myself, Alex Ireland (postdoc, Lehigh University), and Michael Clifford (PhD student, Lehigh University).

Our work this summer was focused on two sites – Triangle Lake and Long Lake.  The first several days were spent measuring basin depths with a probe rod so that maps of the underlying basin morphologies could be developed.  We then collected a series of peat cores at the two sites, located along transects that captured the gradients of basin depth. The peat and sediments will be analyzed for plant remains and carbon content later this summer and fall, and used in conjunction with radiocarbon dating to determine when the peat-mat established in different portions of the basins.  This information will allow us to reconstruct how and when the peat mat expanded at the two sites.  The timing of peat mat expansion will be compared between the two sites, as well as to other sites in the region and to paleoclimate records, to assess the role of climate variability in triggering peat-mat expansion.  Last winter we collected sediment cores from the central lakes that occupy the Triangle and Long Basins, and these will be examined to assess how the lake ecosystem responded to bog-mat advances of the past (see related blog post and video here).  Ultimately the datasets from the lake and peatland components of the ecosystem will be integrated and used to develop a predictive model of bog mat expansion and impacts, which will be used to anticipate potential future changes in these valuable ecosystems.  A short video highlighting some of our activities during the past few weeks is below.

-rkb and awi-

A portion of one day’s field notes.  The stratigraphic boundary between peat and aquatic sediment is not always easy to delineate in the field.  Laboratory analyses are often needed to precisely identify the position of the boundary.

A fun video highlighting some of the fieldwork:

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Posted on July 10, 2012, in Fieldwork, Original Posts, Research and tagged , , , , , , , , , , . Bookmark the permalink. 4 Comments.

  1. Hi Bob, great post, and awesome video. It put in mind of Bloomingdale Bog, so I encoded the old video and put it at Vimeo: http://vimeo.com/45648437. It’s good to see that some things never change.

    Cheers, Chris

  2. Fantastic Chris! I still sometimes use the Bloomingdale video that you put together to introduce paleoecology in classes. Things do change though….I have a lot more gray in my hair and beard than I did in that video.

  3. I love the photo of Triangle Lake. I just visited the bog by Duck Lake in Land o’ Lakes, 17 miles north of Eagle River. Nothing beats bouncing along the edge of a bog.

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