GeoLog

Europe

Could beavers be responsible for long-debated deposits?

Could beavers be responsible for long-debated deposits?

Following her presentation at the European Geosciences Union General Assembly in Vienna, I caught up with geomorphologist and environmental detective Annegret Larsen from the University of Lausanne, Switzerland, about beavers, baffling sediments and a case she’s been solving for the past seven years.

Back in 2012 the German geomorphology community was seriously debating the source of buried black soils, a stark black layer of sediment found in floodplain deposits all over Europe. Such dark sediments are usually associated with organic, carbon-rich materials, like peat. But unlike the other dark deposits, these soils are low in organic carbon, leading to a wide spectrum of ideas about their origin.

“They’re almost everywhere, and many people have had big fights about them and where they come from. Fire might have played a role, or human impact, or a rising water table associated with changes in climate,” explains Larsen.

The soils themselves are quite variable. Some deposits are quite muddy, while some trap fragments of long-dead plants. “They look a little like the relic of a swamp, containing grassy vegetation, sticks, leaves and little nuts, and they’re mainly black,” said Larsen. At the University of Lausanne, Switzerland and the University of Manchester, UK, she and her colleagues have been studying the composition and chemistry of black soils in an effort to understand how they formed.

Recently, Larsen has uncovered a possible connection between the black soil deposits and European beaver habitats. She presented her findings at the annual EGU meeting earlier this month.

The accused: a European beaver. Credit: Per Harald Olson via Wikimedia Commons

The idea began to take shape while Larsen was driving within the Spessart region of Switzerland. During her travels, she had found the soil situated in environments where beaver populations had been dwelling for some 25 years.

“There are huge swamps, what we call beaver meadows. And the vegetation communities are just like the ones found in those deposits,” said Larsen.

This discovery led her to develop a field experiment with the aim to determine whether beavers could be responsible for these puzzling black deposits.

“It’s like a big mystery for me. To find out if the black floodplain soil really come from when there was a widespread beaver population, before humans eradicated the beaver, I need to understand what the beaver does nowadays, and that’s how I started the project.”

Larsen thinks the beaver-created landscapes change with age, and she has been keeping a close watch on four sites across Switzerland and Germany, where beaver communities have been established for up to 25 years.

The long-toothed mammals have striking impacts on the landscape, which differ depending on where they build their dam. Upstream architecture results in beaver cascades, a series of closely packed ponds, each separated by a beaver dam. Down river, efforts go into one ‘megadam’ that stretches across a slow, meandering section of the stream and cause it to spill out into a large swampy floodplain.

The cascades, Larsen describes, are pretty dynamic. “Sediment gets trapped behind each dam, then they get strained, breach and break, causing sediment to flush downstream. It’s collected by the next dam and that then overtops and then that breaks” and the process starts all over again.

One of Larsen’s field sites: the Distelbach beaver reach. Credit: Annegret Larsen

Beaver meadows begin as large expanses of water, ponds teeming with semi-aquatic vegetation. Over time, fine sediment gathers in the ponds. As the sediment builds up, the area becomes a swamp – a patchwork of shrubs, trees, running water and tough, grassy plants. “You definitely get an explosion in diversity, but it’s a complete change, the area becomes a wetland,” adds Larsen.

And the wetland contains plants that resemble those found in the buried floodplain soils.

“For me, it’s fascinating to think about how all our streams would have looked with a beaver in there: before humans impacted those streams, before humans eradicated the beaver, and before [humans] settled there. There must have been beavers everywhere. Every stream would have been a beaver stream. And a beaver stream looks totally different [to what we see today].”

With the deposits all over Europe, it isn’t hard to imagine that, in years past, beavers shaped the streams, swamps and landscapes of the continent. It’s feasible that these regions might have been swampy landscapes at one point in history.

So, are the beavers behind the black soils? “I think we’re on a good path to contribute to this discussion. It’s at least as reasonable as fire and climate,” she replies.

Larsen makes a strong case, but the jury, it seems, is still out.

By Sara Mynott, EGU Press Assistant

Imaggeo on Mondays: High above the top of Europe

Imaggeo on Mondays: High above the top of Europe

Sentinel-2B imaged the highest mountains of western Europe, just the moment an airplane was about to fly over the granite peaks of Grandes Jorasses and cross the border from France to Italy. The passengers on the right side of the plane must have enjoyed a spectacular view on Mont Blanc, just nine kilometers away to the south-west, and Mer de Glace, the longest glacier in France flowing down from its peak.

Note the shadow of the granite “aiguilles” on fresh early winter snow in the upper part of the glacier. The famous Aiguille de Midi is casting its shadow on the village of Chamonix on the top-left, as late autumn colours are still visible on the larch in Val Ferret in the bottom-right corner of the image. Contains Copernicus Sentinel data (2018). Processed with Sentinelflow (v0.1.3).

Description by Julien Seguinot, as it first appeared on imaggeo.egu.eu.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Imaggeo on Mondays: Exploring the underground cryosphere

Imaggeo on Mondays: Exploring the underground cryosphere

The winter season is a good time to take advantage of cold weather activities, whether that’s hitting the ski slopes or warming up by a fire, but for Renato R. Colucci, it’s also one of the best time’s to study the Earth’s underground cryosphere.

Colucci, who took this featured photograph, is a researcher at Italian Institute for Marine Sciences (ISMAR) of the National Research Council (CNR) and is a scientific lead partner for the Cave’s Cryosphere and Climate project, C3 for short. The C3 project aims to monitor, study, date, and model alpine ice cave environments.

This photo was taken by Colucci while he and the C3 project team were surveying a large ice deposit in the Vasto cave, situated within the Southeastern Alps of Italy. Speleologists of the E. Boegan Cave Commission began documenting the caves in this region in the 1960s, making it a great site for studying underground cryosphere today. For the past few years the C3 team has been monitoring the microclimates of these caves as well as analysing how the ice masses within are melting and accumulating ice.

There are many different kinds of ice deposits in caves, but the main difference is how these types accumulate their frozen mass. For some cave ice deposits, like the one featured in this photo, the snowfall that reaches the cave interior amasses over time into solid layers of ice, as is typical for many glaciers. However, other deposits take form when water from melting snow or rain percolates through rock’s voids and fractures, then freezes and accumulates into permanent ice bodies in caves.

These high-altitude underground sources of ice are a lesser-known faction of the cryosphere since they are not very common or reachable to scientists, but still an important one. Often the permanent ice deposits in caves contain pivotal information on how Earth’s climate has evolved over time during the Holocene.

However, if the Earth’s global temperatures keep increasing, this data might not be available in the future. While ice masses in caves are more resilient to climate change compared to their aboveground counterparts, many of these deposits, and the vital data they store, are melting away at an accelerating rate. “Global warming is rapidly destroying such important archives,” said Colucci.

Through this project, the researchers involved hope to better understand the palaeoclimate information stored in these deposits and how the ice will respond to future climate change.

By Olivia Trani, EGU Communications Officer

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.