Biodiversity Reversals in Alpine Rivers

A recent study on the Borgne d’Arolla, a glacier-fed stream in the Swiss Alps, shows that there is less biodiversity among macroinvertebrates than expected in the summer and higher biodiversity than expected in the winter. Chrystelle Gabbud, a geologist at the University of Lausanne in Switzerland, and her associates, found that the rates of streambed disturbance in the Borgne d’Arolla were also much more frequent than normal observations of disturbance in glacial rivers, even during times of peak discharge. The team’s results were published in September in Science of the Total Environment and attribute the above biodiversity inversion phenomenon to the increased frequency of flushing events.

The Borgne d’Arolla (Source: bulbocode909/Flickr).

Why is it that glacier-fed rivers in the Alps are experiencing even more flushing events? Evidence points toward the impacts of global climate change, as rising temperatures influence increased glacial melting and sediment production during the summer months, which in turn means that flushing must be facilitated more often.

Summertime runoff in glacier-fed Alpine rivers is exceptionally useful for supplying water for hydroelectric power production. The flow of water is abstracted at water intakes, which hold back both water and sediment, functioning similarly to dams but on a smaller scale. Intakes also have a relatively low threshold for how much sediment can accumulate before they must be flushed. This means that in basins with high erosion, namely glaciated basins, this flushing happens more frequently. In the summer months, when glacial melt is at its peak, flushing of water intakes can occur up to several times a day. Flushing disrupts the streambed, increases water turbidity, contributes to river aggradation, and negatively affects the macroinvertebrate community both in abundance and biodiversity.

Gabbud and fellow researchers collected samples of macroinvertebrates (animals that do not have a backbone but that are large enough to be seen with the naked eye, such as crustaceans, worms and aquatic insects) at several locations over the course of two years (2016 and 2017) to determine the impacts of flushing water intakes on species biodiversity and abundance. The surrounding tributaries served as controls for the Borgne. The researchers’ findings effectively contradicted the normal expectations for seasonal biodiversity changes.  

Normal biodiversity expectations anticipate that both species richness and abundance should be higher during the summer months, from June to September, which also correspond to the highest water temperatures. However, Gabbud and her team found that biodiversity of macroinvertebrate populations in the Borgne d’Arolla during winter months (and coldest water temperatures) was comparable to the expected levels for the surrounding tributaries during the spring and summer. The Borgne was found to be mostly devoid of life in the summer months, a result which the researchers primarily attribute to the high frequency of flushings.

Figure A depicts the geographical location of the study. Terms in bolded black are the locations of each water intake, and red circles indicate sampling stations. Figure B shows the Bertol Inférieur intake (Source: Gabbud et al., 2018).

The team also compared observations in 2016 to those in 2017. Variations in flushing frequency and duration between the two years led Gabbud and her associates to two determinations. One, that more flushing had a direct negative impact on the presence of macroinvertebrate biodiversity and abundance. Two, that flushings with shorter duration also correlated with higher rates of streambed disturbance.

In addition, they found that as the frequency of flushing decreased, macroinvertebrate populations started to return. Outside of the summer months, flushing happens much less frequently. In a four-day period between flushes, biodiversity was almost able to reach pre-disturbance levels.

A graphical abstract, magnifying both a water intake and a macroinvertebrate species downstream (Source: Gabbud et al., 2018).

The researchers’ observations led them to recommend that the frequency of flushing at the water intakes be decreased and the duration of flushing be increased. They stipulate that higher magnitude flushings, resulting from taking too much time between events, could also have negative impacts. Thus, this situation creates a tension between maintaining hydropower and maintaining biodiversity, a major policy issue.

Currently, Switzerland has a single set of regulations regarding mitigating impacts and restoring ecological areas being used for hydropower generation. There are provisions related to sediment management; however, guidance provided by the Swiss National Government does not mention water intakes by name, instead only addressing dams and maintaining sediment connection.

Seeing as water intakes govern over 50 percent “of hydropower impacted rivers by basin area” in the Swiss Alps, Gabbud and her team emphasize that future regulations must incorporate both sediment management and flow management.

Roundup: Scientific Tensions, Italian Hydropower, and Threatened Biodiversity

Scientific Tensions Among Early Glacier Researchers

From Isis: “Historians of science have long recognized the field as a socially heterogeneous space wherein different groups jostle for access and to assert the priority of their activities… The essay analyzes a dispute between a mountaineer and a scientist-mountaineer that took place at this time, in which the scientist turned to mountaineering ethics to confront accusations of pseudoscience.”

Learn more about the dispute here.

Juneau Icefield Research Project crew, 1949 (Source: American Geographical Society Library, University of Wisconsin–Milwaukee Libraries).

 

Hydropower and Glacier Shrinkage in the Italian Alps

From Applied Energy: “We assess the impacts of nine climate-change scenarios on the hydrological regime and on hydropower production of forty-two glacierized basins across the Italian Alps, assumed exemplary of similar systems in other glacierized contexts.”

Read more about hydropower in the Italian Alps here.

Map of the basins considered in this work. Two of the six basins used for the validation of hydrological model do not have hydropower plants and were therefore not included in the main sample of forty-two basins (Source: Applied Energy).

 

Declining Glacier Cover Threatens Biodiversity

From Global Change Biology: “Climate change poses a considerable threat to the biodiversity of high altitude ecosystems worldwide, including cold‐water river systems that are responding rapidly to a shrinking cryosphere… Using new datasets from the European Alps, we show significant responses to declining glacier cover for diatoms, which play a critical functional role as freshwater primary producers.”

Learn more here.

Relationship between catchment glacier cover and both within
-site β-diversity, (a) – (c), and between-site β-diversity, (d) – (f) (Source: Global Change Biology).

Life on the Rocks: Climate Change and Antarctic Biodiversity

By now, it’s a familiar story: climate change is melting glaciers in Antarctica, revealing an increasing proportion of ice-free terrain. The consequences of this melt are manifold, and one may be surprising: as more ground is bared, Antarctic biodiversity is expected to increase.

Currently, most of the terrestrial biodiversity— microbes, invertebrates, and plants like grasses and mosses— occurs in the less than one percent of continental Antarctica that is free of ice. A recent Nature article predicted that by the end of the 21st century, ice-free areas could grow by over 17,000 square kilometers, a 25 percent increase.

Members of the shrinking Torgersen Island Adélie colony (Source: Rachel Kaplan).

This change will produce both winners and losers in Antarctica’s ecosystems, according to Jasmine Lee, lead author on the above paper, and the game will be problematic. “Some of the winners are likely to be invasive species, and increasing invasive species could negatively impact the native species,” Lee told GlacierHub. “More isn’t necessarily better if new species are alien species.”

The Antarctic Peninsula, an 800-mile projection of Antarctica that extends towards South America,  is one of the fastest-warming places on Earth, and 80 percent of its area is covered by ice. The many outlet glaciers of the Antarctic Peninsula Ice Sheet primarily shrink through surface melting, which reduces volume, while tidal action spurs calving. Lee and her coauthors constructed two models based on two Intergovernmental Panel on Climate Change (IPCC) climate forcing scenarios. Under the strongest IPCC scenario, ice-free areas in the peninsula are expected to increase threefold, and Lee expects biodiversity changes in this region to be obvious by the year 2100. She predicts that some native species will expand their ranges south in response to the creation of new habitat and milder conditions, and invasive species will thrive for the same reasons.

This pattern is already apparent in the distribution of a number of penguin species. As climate warms, sea ice-obligate species like Adélie and Emperor penguin are shifting and contracting their ranges southward, seeking sea ice. Likewise, ice-intolerant gentoo and chinstrap penguins, typical of the Subantarctic latitudes, are moving south as the ocean becomes increasingly free of ice. As temperatures continue to rise, this biogeographic chess will play out increasingly across Antarctica.

Glaciers in the Antarctic Peninsula converge into one calving front (Source: NASA ICE/ Flickr).

“The greater the degree of climate change, the greater the biodiversity impacts,” predicted Lee. She added that counting an Adélie colony in a “real-life ice-free area” was a highlight of her fieldwork.

Interestingly, Lee and her coauthors found that higher biodiversity in the short-term may yield greater homogeneity in the long-term, as invasive species become established and potentially out-compete native species. It’s hard to know how to feel about these ecosystem-wide transitions, said Lee. “The fact that we are driving these changes through anthropogenic climate change should remind us that our actions impact the entire earth, even in what we consider the remotest and most pristine regions. I think we should feel accountable and know that because humans have the power to change the earth, we should do our best to look after it,” she said.

Curious Adélie penguins assess Lee on Siple Island (Source: Jasmine Lee/Twitter).

On June 1, President Donald Trump made a speech announcing the United States’ exit from the Paris climate agreement, obfuscating international cooperation on climate change mitigation. Lee feels this decision sends the wrong message to the rest of the world, but she hopes that the United States will find a way to continue meeting the environmental standards set forth. “America should be a leader in renewable energy technology and policy. However, I am also hopeful that the American businesses and states can reach the Paris accord milestones for America in spite of Trump. And this will show that every city, state or business can have a positive impact regardless of governance,” she said.

No matter the ebb and flow of the political tide, the Antarctic Peninsula is changing. As Antarctic glaciers melt and biodiversity changes, mitigation will require the cooperative efforts of the world.

Roundup: Alpine Streams, Divergence and Ocean Acidification

Roundup: Streams, Oceans and Tiny Flies

Climate Change and Alpine Stream Biology

From Biological Reviews: “In alpine regions worldwide, climate change is dramatically altering ecosystems and affecting biodiversity in many ways. For streams, receding alpine glaciers and snowfields, paired with altered precipitation regimes, are driving shifts in hydrology, species distributions, basal resources, and threatening the very existence of some habitats and biota. Alpine streams harbour substantial species and genetic diversity due to significant habitat insularity and environmental heterogeneity. Climate change is expected to affect alpine stream biodiversity across many levels of biological resolution from micro- to macroscopic organisms and genes to communities.”

Learn more about alpine stream biology here.

An alpine stream in Banff Canada (Source: Bernard Spragg/Flickr).
An alpine stream in Banff, Canada (Source: Bernard Spragg/Flickr).

 

Ecological Divergence of the Alpine Mayfly

From Molecular Ecology: “Understanding ecological divergence of morphologically similar but genetically distinct species – previously considered as a single morphospecies – is of key importance in evolutionary ecology and conservation biology. Despite their morphological similarity, cryptic species may have evolved distinct adaptations. If such ecological divergence is unaccounted for, any predictions about their responses to environmental change and biodiversity loss may be biased. We used spatio-temporally replicated field surveys of larval cohort structure and population genetic analyses (using nuclear microsatellite markers) to test for life-history divergence between two cryptic lineages of the alpine mayfly Baetis alpinus in the Swiss Alps… Our results indicate partial temporal segregation in reproductive periods between these lineages, potentially facilitating local coexistence and reproductive isolation. Taken together, our findings emphasize the need for a taxonomic revision: widespread and apparently generalist morphospecies can hide cryptic lineages with much narrower ecological niches and distribution ranges.”

Read more about ecological divergence here.

A common species of mayfly (Source: Luc Viatour/Creative Commons).
A common species of mayfly (Source: Luc Viatour/Creative Commons).

Ocean Acidification in the Antarctic Coastal Zone

From ScienceDirect: “The polar oceans are particularly vulnerable to ocean acidification; the lowering of seawater pH and carbonate mineral saturation states due to uptake of atmospheric carbon dioxide (CO2). High spatial variability in surface water pH and saturation states (Ω) for two biologically-important calcium carbonate minerals calcite and aragonite was observed in Ryder Bay, in the coastal sea-ice zone of the West Antarctic Peninsula. Glacial meltwater and melting sea ice stratified the water column and facilitated the development of large phytoplankton blooms and subsequent strong uptake of atmospheric CO2 of up to 55 mmol m-2 day-1 during austral summer. Concurrent high pH (8.48) and calcium carbonate mineral supersaturation (Ωaragonite ~3.1) occurred in the meltwater-influenced surface ocean… Spatially-resolved studies are essential to elucidate the natural variability in carbonate chemistry in order to better understand and predict carbon cycling and the response of marine organisms to future ocean acidification in the Antarctic coastal zone.”

Read more about ocean acidification here.

The majestic scenery of Antarctica (Source: Reeve Joliffe/Flickr).
The majestic scenery of Antarctica (Source: Reeve Joliffe/Flickr).

Rocks and Rain Fix Nitrogen in Post-Glacial Sites

A new study in Plant and Soil found that the input of nitrogen from the atmosphere, via a process of rain funneling through rocks, created levels of nitrogen that are adequate to support plant growth in post-glacial alpine soil, challenging the common view that the element is the primary limiting factor in deglaciated areas.

In fact, the researchers found that phosphorous, due to the low-weathering rates and high nitrogen deposition of the region, is the element in soil which limits post-glacial plant life colonization. The team was lead by Hans Göransson of the University of Natural Resources and Life Sciences, Vienna.

The finding challenges the widely-held view that the only plants capable of colonizing post-glacial environments are species that are able to fix nitrogen from the atmosphere. Instead, as this work shows, natural processes enable other plants to become colonizers in the European Alps.

Nitrogen-fixing plants on a post-glacial site in Glacier Bay, Alaska. (Photo:Elizabeth/Flickr)
Nitrogen-fixing plants on a post-glacial site in Glacier Bay, Alaska. (Photo: Elizabeth/Flickr)

This research may have implications for future ecosystem plant colonization and biodiversity, a topic of interest to scientists as glaciers retreat and expose new soils in many regions of the world.

The team, focusing on Damma Glacier in Switzerland, found that the expected nitrogen-fixing plants were usually absent in the early stages of these post-glacial sites, contradicting what previous research has suggested. The study’s findings differ from the research done in recently deglaciated areas in Glacier Bay in Alaska and on the Franz Josef glacier in New Zealand, which show an abundance of nitrogen-fixing plants in post-glacial sites.

Most plants are unable to process atmospheric nitrogen directly and can only absorb it once it undergoes a transformation within the soil. (Nitrogen is essential for plant growth.) Some plants, however, undergo a process called nitrogen fixation which converts atmospheric nitrogen into a form useful for them. Bacteria in the plant’s roots help, as they are able to convert the nitrogen into a usable form.

Because of this capacity, nitrogen-fixing plants are generally thought of as the colonizing species in post-glacial sites, since these rocky areas are typically so low in soil nitrogen that plants that cannot fix nitrogen would not be able to grow. Once the nitrogen-fixing plants begin to die and the nutrients from them return to the soil, a more diverse second generation of plants can grow.

Damma Glacier in Switzerland. (Photo:Paebi/Wikimedia Commons)
Damma Glacier in Switzerland. (Photo: Paebi/Wikimedia Commons)

The team set out to explore how plants in the region were colonizing even when nitrogen-fixing plants were not present. They found that nitrogen from the atmosphere was deposited into the soil by newly exposed rocks, which acted as funnels when it rained. This process provided sufficient amounts of nitrogen for plant growth, and thus allowed non-nitrogen fixing plants to grow in these areas.

The researchers divided the Damma post-glacial area into a total of 21 sites across three time periods related to the age of the soil since the glacier retreated: pioneer (fewer than 16 years since deglaciation), intermediate (57-80 years), and late-stage (108-137 years). The Damma glacier has had a long and well-tracked retreat, making the separation of time periods easy.

The team used ion exchange resin bags at each site that measure the amount of nitrogen in the soil. They also took the above-soil measurements by collecting the biomass growing at the sites and analyzing the nitrogen levels.

They found that nitrogen levels were high in the pioneer stage, followed by low levels in the intermediate, and high levels again in the late stage.

As the nitrogen channels through rocks and into the soil, it creates an overabundance of nitrogen at first, since there is little or noplant life to use the element. This process eventually creates hotspots of plant growth, but as soil and organic matter increases, the rocks become covered. Once the rocks are covered, the atmospheric nitrogen can no longer be deposited into the soil. This, along with the increased presence of plants using the soil nitrogen, leads to a decrease in nitrogen availability within the soil in the intermediate stage.

High levels of nitrogen return in the late-stage sites once the vegetation has matured and therefore requires less of the element for growth. With more plant cover, nitrogen increases as plants die and the nutrients are returned to the soil through decomposition.  

Schematic from the study showing the build up of soil and plant matter on top of the rocks. This eventually stops the funneling process found in early stages. (Figure:by Kristel Perreijn)
Schematic from the study showing the build up of soil and plant matter on top of the rocks. This eventually stops the funneling process found in early stages. (Figure:Kristel Perreijn)

The team also looked at phosphorous, another important element for plant growth, and found little difference in its levels in the soil, regardless of the time since deglaciation. Since nitrogen levels changed with time, the ratio of phosphorus to nitrogen also varied. The researchers found that phosphorus stabilized at a low level. When the nitrogen levels were high, in the pioneer and late stages, phosphorus was the limiting element. This relationship flipped in the intermediate stage when nitrogen availability was low. Thus, as the nitrogen availability changes, so too does the element that is limiting plant growth.

The researchers concluded that colonizing plants found in the bedrock typical to the Alps are more likely to be limited by phosphorous due to the high levels of nitrogen deposition and the low weathering rates needed to release phosphorus from minerals. This gives an advantage to plants that can use the phosphorus from mineral sources, thus affecting the composition of the plant life in those areas throughout the different stages of deglaciation.

“In succession, the next set of species coming in is dependent on [those] already present. Thus a change in primary succession may lead to dramatic change in the plant community later on,” Göransson, the lead author, told GlacierHub in an email interview.