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.

Future Unwritten: Antarctic Sea Pens’ Secrets to Success

A sponge, Haliclonissa verrucosa, filter feeds in water off of Spume Island (Source: Chuck Amsler).

On the seafloor, beneath the cold, dark waters surrounding Antarctica, life blooms. Sea stars make their glacially-slow journeys along rocks, sponges rhythmically pulse water through their internal cavities, and one particular coral, the delicate sea pen Malacobelemnon daytoni, flourishes.

Sea pens are colonial, meaning that many individuals work together as a whole, each conducting a specialized task necessary for survival. The resulting shape resembles a quill pen, earning them their creative common name.

M. daytoni is one of the most abundant species in Potter Cove, located off the southwest side of King George Island in the South Shetland Islands. The environment of Potter Cove is heavily influenced by local glacial retreat, which discharges increasing quantities of sediment into the ocean. Researchers know little about benthic (defined as the lowest layer in a body of water) ecology in this region, challenging as it is to conduct scientific research in the cove’s remote, frigid waters. A recent paper in Marine Environmental Research by an international team from the Universidad Nacional de Córdoba and Institute of Marine Science analyzed the biochemistry of M. daytoni to understand its ecological success. They found that the key is a flexible, omnivorous diet and strategic reproductive techniques.

A sea pen in Potter Cove (Source: Ricardo Sahade).

Natalia Servetto, lead author on the study, is part of a group that has been studying the Potter Cove benthos since 1994, thanks to logistic support of the Instituto Antártico Argentina, the Alfred Wegener Institute and the National Scientific and Technical Research Council (CONICET). These efforts have revealed what Servetto called an “unexpected and marked shift in the system… linked to ongoing climate change processes” and to glacial retreat, which has increased sedimentation rates, affecting the benthic fauna. In the last few years, Servetto says, the abundance and distribution of M. daytoni has increased significantly, while many other Potter Cove invertebrates are becoming less abundant.

Why should the sea pen thrive while its neighbors perish? To answer this question, a team based out of the Argentine Carlini Station scuba dove every month for one year, sometimes through holes in the sea ice, to depths of 15 meters to take tissue samples from sea pens in Potter Cove.

This in itself is a feat. Chuck Amsler, a biology professor at University of Alabama at Birmingham who studies macroalgae and invertebrates in the Western Antarctic Peninsula, told GlacierHub that diving to study Antarctic life is a challenge because, “It’s damn cold!” However, Amsler added, “The scientific reward is that you have the opportunity to observe your study system directly. There is no substitute for the kind of insights one can get from that.”

Carlini Station provides access to the remote Potter Cove (Source: Natalia Servetto).

Many such insights came to fruition back in the lab, where the researchers analyzed the carbohydrate content, stable isotope ratios, and fatty acids in the coral tissues, looking for chemical clues to what the pens eat through the year. Just as a savvy New Englander might buy groceries with the seasons, eating peaches in summer, apples in autumn, root vegetables in winter, and fresh maple syrup in spring, the researchers found that the sea pen’s diet changes seasonally. In summer, M. daytoni feasts on copepods (a type of small invertebrate), phytoplankton, and a bit of macroalgae detritus. In autumn, the menu features more phytoplankton and microalgae, and in winter, macroalgae detritus and sediment are the sea pens’ bread and butter. In spring, their diet becomes fresher again when phytoplankton and microplankton return to the table.

This omnivorous, opportunistic feeding strategy allows the sea pens to eat whatever is available in a given season, reducing pressure on the species during times of food depletion. Such depletion peaks in winter and autumn, forcing M. daytoni to scavenge for organic sediment and detritus that become re-suspended from the seafloor. Sea pens have another major advantage over their neighbors: inorganic sediment from melting glaciers can clog the respiration and feeding mechanisms of filter-feeding invertebrates, while M. daytoni continues to chow down, undisturbed.

Amsler and his team begin a dive to study benthic macroalgae and invertebrates (Source: Maggie Amsler/Antarctic Photo Library).

Not only do they feed resourcefully, but the sea pens also optimize the energy they obtain. Servetto’s team found that lipid content in their tissues, associated with reproduction, increased in rapid bursts that were seasonally linked with higher food availability. This pattern suggests that sea pens can take the energetic resources offered by the environment at a given time and shunt them into reproduction, the most important process for any organism.

Beyond any single year, and beyond the bounds of the Potter Cove ecosystem, the opportunistic feeding and reproductive strategies of M. daytoni will help this species thrive. Nearly 90 percent of glaciers are retreating along the Antarctic Peninsula, causing environmental shifts that threaten many species, but could create an opportunity for sea pens to actually expand their range, Servetto says. As glacial retreat creates new ice-free areas, colonization may occur, according to Servetto, “at a previously unimagined speed.”

However, it’s not yet clear how the Antarctic coastal system will evolve as glaciers melt. Amsler says that decreasing sea ice cover will likely favor macroalgae and their associated communities of small, mobile invertebrates like amphipods and gastropods, and threaten shallow-water sessile invertebrates like the sea pens, probably pushing them into deeper water. Decrease in sea ice cover may also have broader climate impacts: the Antarctic benthos is a net carbon sink (a natural process that stores carbon), and as ice cover decreases, Amsler expects that benthic primary production will increase, removing even more carbon from the atmosphere.

Divers in Antarctica face difficult conditions, including brash ice (Source: Chuck Amsler).

No matter the outcome, the impacts of climate change on benthic Antarctic invertebrates will be manifold. Other forces, like ocean warming and acidification, will also affect M. daytoni and reshape benthic invertebrate communities, though Amsler says more work is needed to understand how. “I don’t know what the community will look like in 100 years, but I’m confident that it will be different from what we see today,” he predicted. As climate changes and glaciers melt, the flexible diet and efficient reproductive strategy of M. daytoni will give it an advantage in changing Antarctic coastal ecosystems.

Study shows glacial melting changes mountain lake ecology

In the Rocky Mountains, researchers have been studying a pair of lakes–Jasper and Albino. While they are similar in size, location, and depth, there is one important difference: Jasper Lake is fed by glacier meltwater while Albino Lake is fed by snow. A report published in May reveals that this small difference has had a dramatic impact on the biology and chemistry of the lake itself, indicating that water source plays a much larger role in the ecological health of mountain lakes than previously thought.

Hallett Peak, Rocky Mountain National Park (source: NPS)
Hallett Peak, Rocky Mountain National Park (source: NPS)

Mountain lakes are an important source of regional water in the western United States, and are known for their historically high levels of biodiversity. Recently, these lakes have seen rapid changes which sparked concern from the scientific community. Last month the California-based Consortium for Integrated Climate Research in Western Mountains (CIRMOUNT) addressed the need for research on mountain lakes by publishing a special feature of Mountain Views, their biannual report compiling recent research on western United States mountains, that focuses exclusively on mountain lakes. The ten featured research articles all point to the importance of alpine lake conservation and investigate the impacts of climate change and other anthropogenic influences on regional ecology and environmental health.

One article— “Effects of Glacier Meltwater on the Algal Sedimentary Record of an Alpine Lake in the Central U.S. Rocky Mountains”— studied glacier-fed and snow-fed lakes and found drastic differences in the chemical compositions and species ecology between the two. The researchers, Krista Slemmons of the University of Wisconsin, Stevens Point, and Jasmine Saros of the University of Maine chose two alpine lakes in the Beartooth Mountains, Jasper and Albino, which are physically and geographically similar. However, Jasper Lake is fed by a glacier meltwater, while Albino Lake is only fed by snowmelt.

core samples (wiki)
core samples (wiki)

To determine differences in the lakes’ histories, sediment cores were taken from the bottom of the Jasper and Albino. Over time, organisms and nutrients accumulate on the lakebed and gradually build up as sediment in bodies of water. The layers of the core therefore tell a story about the history of the life within the lakes. By analyzing the sediment cores, the researchers were able to look back through time and see how the type of water feeding the lakes has led to differences in life history and biogeochemical cycling.

Within the Jasper core, researchers found high levels of plankton species that thrive in high nitrogen conditions, indicating that the lake has had higher nitrogen levels than Albino Lake over the past 3,000 years, with particularly high levels corresponding to periods of high glacial melting, most notably the 20th century.

fresh-water phytoplankton, used to determine historic water ecology and nutrient levels (wiki)
fresh-water phytoplankton, used to determine historic water ecology and nutrient levels (wiki)

Today, glacier-fed Jasper Lake has approximately 63 times more nitrogen than snow-fed Albino Lake. It is the high concentrations of nitrogen in the glacial meltwater that has led to the differences between the lakes. This trend will continue as glacier melting accelerates with climbing temperatures.

While nitrogen is an important nutrient, and often limited in alpine lakes, it is possible to have too much of a good thing. In Jasper Lake, the sediment cores also indicated that species richness, or the number of different types of species present in an ecosystem, was lower than in the nitrogen-limited Albino Lake. These findings suggest that a high influx of glacial meltwater into lakes may lead to eutrophication.

algal bloom from eutrophication (flickr)
algal bloom from eutrophication (flickr)

Eutrophication is a type of water pollution that occurs when high levels of nitrogen cause plant and algae to grow excessively. This phenomenon, known as an algal bloom, blocks sunlight from penetrating the water column, decreases the oxygen levels in the water, and can harm other species in the ecosystem. Eutrophication is most commonly seen as a result of nitrogen fertilizer runoff into bodies of water, but the nitrogen stored in glacier ice appears to have high enough concentrations to cause the same negative impacts.

While global water scarcity is enough cause for concern over glacier retreat, these findings suggest that glacier melt has wider reaching negative impacts on ecosystem function than previously recognized. Understanding the cascade of environmental impacts resulting from glacial melting will become increasingly important as temperature rise continues to break global records, and will play an important role in preserving the biodiversity of marine ecosystems.

The Challenge of Sediment Management

Moinak Hydro Power Plant.
Moinak Hydro Power Plant, on the Sharyn River in Kazakhstan. (Photo: Wikipedia Commons)

A new research study entitled “Ecosystem impacts of Alpine water intakes for hydropower: the challenge of sediment management” explores the effects of different hydropower capture techniques on human and ecosystem water needs. Rivers fed by glacial melt and snowmelt in Alpine regions serve as a critical resource for hydroelectric power production. However, the management systems used in hydroelectric systems heavily impact both river and sediment flow. This disruption, in turn, heavily, and often negatively, impacts downstream communities and ecosystems, which face consequences of habitat change, degradation, and temperature increases. The authors note that few policy solutions are currently available to reduce and manage these impacts, and call for fresh ideas to address them.

The cover image of the Wiley' January/February 2016 issue.
Researchers taking measurements at a stream gauge (Photo: Jim Constanz)

The study, published in the latest January/February issue of Wiley Interdisciplinary Reviews: Water, reviews the three main types of water management techniques used in hydropower systems. Dams impound water behind barrages in a valley, while abstraction removes water from a ground source. Once abstracted, water is moved laterally (shifted nearby) or downstream (to a lower part of a river) in order to reach the hydroelectric plant.

The article systematically examines how these different methods impact water and sediment flow of the river. Though previous work has studied the impact of different types of water management techniques on river flow, this study is the first of its kind to closely investigate the impact of water abstraction and transfer systems on sediment displacement, which, the study argues, “can significantly influence habitat, which in turn impacts ecosystems.”

The disruption and transfer of sediments have important impacts on human and natural ecosystems because they interfere with what the researchers call the “the natural sediment ‘conveyor belt’” — the process of sediment transfer that is usually determined by natural processes such as erosion, abrasion, sorting, and deposition. Though rivers primarily transport water, they are also vital vessels of sediment transfer. Fine sediment particles enter the river as the water erodes the banks, or tiny fragments break off from rocks in the water. The river carries these particles downstream, allowing the larger ones to drop out—or be deposited—in places where currents slow down.

Disruption of water and sediment flow puts Alpine ecosystems, whose flow regimes are a “key driver” of their physical habitat, at risk. Alpine habitats face risk of physical habitat change, degradation, temperature increases, and major changes to riparian vegetation. Previously inundated rivers may become dry. Such rapid changes in stream flow may leave Alpine fish not able to adapt quickly enough to sustain these alterations. Water abstraction may also “induce lower or higher nutrient levels, depending on the geology; increase electrical conductivity depending on the solute-richness; and/or increase pH.”

Chilime Hydropower Dam
The Chilime Hydropower Dam in Nepal. Image credit: Wikipedia (Photo:Wikipedia Commons)

In order to guarantee both human and ecosystem water needs and minimally disrupt natural sediment transfer processes, hydroelectric systems and water management systems must replicate as close to a natural flow regime as possible. However, attempts to mimic variables of water magnitude, frequency, duration, timing, and rate of charge of each river are unlikely to be met due to simple “constraints of hydroelectric production,” the researchers note. Natural river and sediment flows fluctuate seasonally, making them difficult to mimic because hydropower systems are designed to operate with steady, slow flows. These flows, in turn, rarely provide enough speed to carry larger particles, but also never slow enough to allow smaller particles to settle.

The researchers offer several suggestions to reduce the impacts of sediment transfer on downstream ecological and human communities. They seem some promise in sediment management processes, such as reducing sediment flushing during flows, creating artificial sediment sinks, and finding ways to permanently accumulate remaining sediment into floodplain systems. Such management processes, the researchers noted, are “rarely considered in legislation designed to create more environmentally sustainable river flows.” As such, their suggestions create important policy implications for alpine and glacial river communities near hydropower facilities.

Reinforsen power plant, norway
The Reinforsen power plant in Mo i Rana, Norway. (Photo: Flickr/Statkraft)

However, researchers noted that it is still difficult to determine best practice procedures for sedimentation management which could improve river ecology. They comment that “[t]his is a particular problem for water intake systems where there are almost no experiments, and hence scientific bases, that might be used to define the kinds of instream flow needs necessary.”

Though hydropower poses promise for clean, alternative energy, the study introduces underlying environmental tensions between clean energy solutions and the negative impacts of such alternative energy sources on surrounding communities and ecosystems. In this way, it alerts policy-makers and the public at large to challenges in bringing about a successful transition to low-carbon energy systems. economies and societies.