Global warming is altering glacier-fed stream ecosystems around the world

According to two recent studies conducted as part of the Vanishing Glaciers Project, the ecosystems of glacier-fed streams are undergoing profound changes around the world. This could have major implications for the food chain and the natural carbon cycle.

Glacier-fed stream ecosystems have survived harsh, nutrient-poor environmental conditions for thousands of years, but are now being transformed by climate change at an unprecedented rate. That’s the conclusion of two studies published by scientists from EPFL’s River Ecosystems Laboratory (RIVER), part of EPFL’s Faculty of Architectural, Civil and Environmental Engineering (ENAC). The studies were conducted in collaboration with the Luxembourg Center for Systems Biomedicine (LCSB) at the University of Luxembourg and the King Abdullah University of Science and Technology. The first study highlights the diversity and adaptive strategies of the microbiome in glacier-fed streams, while the second reveals that the decomposition of organic matter in glacier-fed streams s is accelerating and the structure of the microbiome is changing as the glaciers shrink. As organic matter decomposes at a faster rate, glacier-fed streams may become more important to the natural carbon cycle.

Stream at the foot of the Shkhelda glacier, in the Caucasus, photographed by the RIVER Laboratory team that took biofilm samples.© Matteo Tolosano/ EPFL

From the green oasis to the forests

Climate change is making the spring and fall seasons in glacier-fed streams last longer. According to the first study published in Nature Communications, this change has major repercussions on the microbiome of the ecosystem, which until now was akin to a “green oasis” for short periods in spring and autumn. In the future, the microbiome may turn into something more like a “forest.” “These seasons are important ecological ‘windows of opportunity’ in glacier-fed streams with less harsh environmental conditions. This allows primary producers to proliferate and they form the energy base of the microbial food chain,” says Professor Tom Battin, Director of RIVER and corresponding author of both publications.

In addition to this discovery, the study sheds new light on what was once a black box: the microbiome inside these ecosystems. Scientists now have a better understanding of how different microorganisms compete or help each other to survive in such a nutrient-poor environment with alternating periods of freezing, melting and intense UV radiation.

The RIVER laboratory team at work on Antisana, a 5758 meter high stratovolcano located in the Andes Cordillera, Ecuador. © Matteo Tolosano/EPFL

We can expect the food web of glacier-fed streams to become greener in the future as primary production becomes more important.

Slimy Megacities

The scientists also unveiled potential metabolic interactions between algae and bacteria and showed that biofilms can recycle food streams internally. This appears to be an important adaptation for surviving in an energy-poor ecosystem. “Scientists in our field tend to call biofilms ‘slime megacities’ because they harbor millions of microbial residents encapsulated in mud and attached to rocks,” says Battin. “We were able to observe how the different species work together to survive.” Other crucial discoveries made by the RIVER team were an unexpectedly rich virome and genomic features that may explain how bacteria are able to protect themselves against freezing temperatures.

Camp of the RIVER Laboratory team at the foot of Ama Dablam, which culminates at 6812 meters, in Nepal, in the Everest region. © Matteo Tolosano/EPFL

Accelerate the carbon cycle

In the second study, published in Global Change Biology, scientists found that organic matter in 101 glacier-fed streams around the world decomposes faster as glaciers shrink. At the same time, they were able to link this ecosystem process to distinct components of the microbiome. “We can expect the food web of glacier-fed streams to become greener in the future as primary production becomes more important,” says Battin. “With this change, some microbial species could die out, others thrive, and there will be a shift all the way up the food chain.” The gist of this study is that as glaciers shrink, their streams may become more significant natural sources of CO2 to the atmosphere.

Greenland. © Myke Styllas / EPFL

Our unique effort, which combines intense expeditions with genomic analysis, has made us the first to systematically study the microbiome of these ecosystems, which are now changing with melting glaciers.

Last stop: Alaska

This research was made possible by the Vanishing Glaciers project, a four-year project based at EPFL and funded by the NOMIS Foundation. As part of this project, RIVER scientists began sampling glacier-fed streams around the world in 2018 with the aim of deciphering the biodiversity of these endangered ecosystems. “Our unique effort, which combines intense expeditions with genomic analysis, made us the first to systematically study the microbiome of these ecosystems, which are now changing with melting glaciers,” says Battin.

The Vanishing Glaciers expedition will soon be coming to an end and will make its final stop this summer in Alaska. Scientists have only analyzed 20% of the data they have collected so far on more than 150 glacier-fed rivers around the world. Future analyzes will investigate precisely how the microbiome is altered – and what the broader ramifications are.

The RIVER laboratory team in the Rwenzori Mountains, Uganda. © Matteo Tolosano/EPFL