Roundup: Glacier-Fed Lakes, Remote Sensing, and Glacial Succession

Roundup: Glacier-Fed Lakes, Remote Sensing, and Soil

 

Global Warming and Glacier-Fed Lakes

From Freshwater Biology: “Climate warming is accelerating the retreat of glaciers, and recently, many ‘new’ glacial turbid lakes have been created. In the course of time, the loss of the hydrological connectivity to a glacier causes, however, changes in their water turbidity (cloudiness) and turns these ecosystems into clear ones. To understand potential differences in the food-web structure between glacier-fed turbid and clear alpine lakes, we sampled ciliates (single-celled animals bearing ciliates), phyto-, bacterio- and zooplankton in one clear and one glacial turbid alpine lake, and measured key physicochemical parameters. In particular, we focused on the ciliate community and the potential drivers for their abundance distribution.”

Learn more about how global warming affects lakes here:

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A glacier-fed lake (Source: Rodrigo Soldon/Creative Commons).

 

Glacier Remote Sensing Using Sentinel-2

From Remote Sensing: “Mapping of glacier extents from automated classification of optical satellite images has become a major application of the freely available images from Landsat. A widely applied method is based on segmented ratio images from a red and shortwave infrared band. With the now available data from Sentinel-2 (S2) and Landsat 8 (L8) there is high potential to further extend the existing time series (starting with Landsat 4/5 in 1982) and to considerably improve over previous capabilities, thanks to increased spatial resolution and dynamic range, a wider swath width and more frequent coverage.”

Read more about remote sensing here:

Test region 1 in the Kunlun Mountains in northern Tibet using a S2A image from 18 November 2015 (Source: Remote Sensing).
Test region 1 in Tibet using a S2A image from 2015 (Source: Remote Sensing).

 

The Impact of Soil During Glacial Succession

From Journal of Ecology: “Plant–soil interactions are temporally dynamic in ways that are important for the development of plant communities. Yet, during primary succession [colonization of plant life in a deglaciated landscape], the degree to which changing soil characteristics (e.g. increasing nutrient availabilities) and developing communities of soil biota influence plant growth and species turnover is not well understood. We conducted a two-phase glasshouse experiment with two native plant species and soils collected from three ages (early, mid- and late succession) of an actively developing glacial chronosequence ranging from approximately 5 to <100 years in age.”

Learn more about the impact of soil during glacier succession here:

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A photo of Lyman Glacier with different plants growing on its face (Source: Marshmallow/ Creative Commons).

 

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As Temperatures Rise, Poplars Replace Alaskan Tundra

In Alaska’s Denali National Park, summer temperatures have risen 2 degrees Celsius over the past century, with the majority of change occurring since the 1970s. The glaciers that cover 1 million square miles of the park are melting rapidly, exposing bare earth where there once was ice.

An Ecosphere study, published July 19, finds that the rising temperatures impacting the glaciers are also affecting the plant communities that grow in newly exposed areas, fundamentally altering the Alaskan landscape and ecosystems.

View of Denali from Stony overlook (Credit: NPS Photo / Jacob W. Frank)
View of Denali from Stony overlook (Credit: NPS Photo / Jacob W. Frank)

The research team, led by Carl Roland and Sarah Stehn, investigated how the Alaskan landscape near Denali’s Muldrow Glacier changed over time by recreating a study conducted 54 years ago by Leslie Viereck. In 1966, prior to the 2 degree temperature rise, Viereck set out to determine the plant succession in the area. Succession is the process of an ecosystem evolving over time. In mountain regions, it can occur when a glacier retreats or a river forms an outwash plain, and a new community of vegetation can grow.

Viereck studied the outwash plain of the McKinley River, which flows west out of Muldrow Glacier, and examined areas ranging from 1 to roughly 5,000 years old. Based on his observations, he determined that the bare rocky plain would transition into a meadow, followed by small shrubs and eventually becoming a tundra ecosystem, with thick moss and a low canopy of shrubs.

Half a century later, Roland, Stehn and their colleagues were able to replicate Viereck’s study to see if the temperature change has impacted the successional path laid out by their predecessor. Using a series of photographs, GPS, field notes and re-measured areas of land, the team found surprisingly different results. The newly exposed areas were not transitioning into meadows, but instead covered in balsam poplar trees. The new Alaskan landscape showed signs of succeeding into a forest rather than tundra—representing a completely different biome change.

Photographs of the Muldrow Glacier study area from the original and current study (source: Ecosphere)
Photographs of the Muldrow Glacier study area from the original and current study (source: Ecosphere)

According to the study, the temperature rise fundamentally altered the climatic conditions of the ecosystem, and as time passes, the differences become increasingly larger. Like an archer shooting an arrow hundreds of meters away, even a small shift in the starting point can change the trajectory completely, and yield a very different outcome in the ecosystem structure and function.

The poplars began to grow in the early succession landscape because they thrive in the warming climate, and require warmer soils to grow. Once the trees were established, they had the competitive advantage over other plant species—they produce seeds early and abundantly, and are able to thrive in bare soil when other species are not yet present. Once the trees begin to grow, they alter the landscape by blocking the sun from smaller plants, and allowing a different range of species to thrive. Both plants and animals that prefer woodland instead of tundra move to these newly formed forests. The trees also block the wind, allowing snow to build up where it previously would have been blown away. The thick layer of snow prevents permafrost from forming, keeping the soils warm. This one species, through a series of chain events, is able to colonize the area and alter both the species and climate of the region.

Balsam Poplar canopy (source: Adam Jones, PhD)
Balsam Poplar canopy (source: Adam Jones, PhD)

While the newer areas of exposed land showed a dramatic shift in the projected succession, the older, more established areas of the landscape followed the path as predicted by Viereck. The areas located farther from the river and the end of the glacier plain had begun to grow before the temperature increase. Once the ecosystem had begun to develop, it is much more difficult to change its course. While poplars were still found in these areas, they had a much smaller impact on the ecosystem as a whole.

As temperatures continue to rise and glaciers continue to retreat in Alaska, there will be large areas of land exposed which will be colonized by vegetation. Ecosystems will form in place of the ice, and when they do, they will be woodlands rather than the iconic Alaskan tundra.

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How Invertebrates Colonize Deglaciated Sites

Mitopus morio (Source: Javier Díaz Barrera/Flickr).
Mitopus morio (Source: Javier Díaz Barrera/Flickr).

Scientists have long wondered how species colonize sites after deglaciation. A recent study by Amber Vater and John Matthews in the journal The Holocene of invertebrates–animals without backbones—on a number of sites in Norway advances the understanding of this colonization. It pays particular attention to succession, the processes of change in the species composition of ecological communities over time. The invertebrate groups which were studied include insects, spiders and mites, as well as harvestmen, also known as daddy longlegs.

To study the process of succession, Amber and Matthews collected invertebrate samples from pitfall traps in 171 locations across eight glacier forelands, which deglaciated over the last few centuries, in the Jotunheimen (high altitude) and Jostedalsbreen (low altitude) subregions in southern Norway. Jotunheimen is the highest mountain in Europe north of the Alps and west of the Urals, while Jostedalsbreen is the largest ice-cap in Europe outside Iceland. These forelands represent different ecological regions and areas that have been deglaciated for periods of different length. A variety of geological and biological evidence allowed the researchers to establish the precise timing of glacier retreat across their sites. The researchers identified the organisms by taxa—the species, genus or family to which they belong—since species identification was difficult in some cases.

The location of the eight glacier forelands in southern Norway (Source: Vater and Matthews/Sage Journals).
The location of the eight glacier forelands in southern Norway (Source: Vater and Matthews/Sage Journals).

Several major findings were derived from this study. Firstly, invertebrates arrive fairly quickly after the retreat of glaciers, within a decade or two. In particular, initial colonization is faster and dispersal is more effective at high altitudes, where glacier forelands are small, reducing the distance from established communities to new sites; in addition, the strong winds in such areas can carry organisms further. The flying insects, such as flies, aphids, bees, wasps, stoneflies, caddisflies and flying beetles, arrived earlier than the ground-active non-flying species, such as spiders, harvestmen, mites, ants, and non-flying beetles. Moreover, the communities grow more complex over time. In the first stage, lasting about 20 years, 11-31 taxa were found; this number increased to 21-55 in the fourth and final stage, over two centuries later. The authors found as well that invertebrate communities tend to be more diverse at low altitudes, where environmental conditions are more favorable.

Jotunheimen from southern Norway (Source: Thomas Mues/Flickr).
Jotunheimen from southern Norway (Source: Thomas Mues/Flickr).

Vater and Matthews summarize their findings by stating “invertebrate succession on the glacier forelands is viewed as driven primarily by individualistic behavior of the highly mobile species with short life-cycles responding to regional and local abiotic environmental gradients”.

Amara quenseli (Source: Chris Moody/Flickr).
Amara quenseli (Source: Chris Moody/Flickr).

This research calls into question earlier studies of succession. Previous studies, often based on plant species rather than invertebrates, have emphasized that nearly all taxa occur only in some of the stages of succession. By contrast, Vater and Matthews find that most of the taxa that first appear remain all the way till the final stage—65-86%, depending on the site. The authors describe their results as an ‘addition and persistence’ model (because taxa remain, once they arrive) rather than the more established ‘replacement-change’ model, in which different taxa replace each other over time. This ‘addition and persistence’ model seems to be more applicable in severe environments.

This research offers some insights into the regions that will become exposed as glacier retreat continues. It brings the positive finding that lands that appear after glacier retreat will not remain barren for long, since invertebrates are likely to colonize these sites soon. However, the new areas at higher elevations may have only a small number of specialized invertebrate taxa instead of a wide range of them.

For more details on invertebrates living on glaciers, look here.

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