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Newly Formed Glacial Lakes Reveal How Ecosystems Form
August 7, 2026 |
Glacier retreat is rapidly transforming landscapes, creating thousands of new lakes that are then colonized by plants and animals. In these natural laboratories scientists can study how ecosystems develop, from a largely mineral environment to a complex food web, a process known as ecological succession. While the physical effects of glacier retreat are well documented, much less is known about how these changes affect the availability of organic nutrients – the molecules that animals need to survive.
Fish, like many animals, can only produce limited amounts of essential organic nutrients, such as omega-3 fatty acids themselves and need to obtain them from their diet. These essential organic nutrients are produced primarily by algae or bacteria and are passed through the food web to fish, which obtain them by feeding on algae directly or on organisms that have consumed them.
Arctic char as indicators of nutrient pathways
Eawag researchers investigated at what quantity these essential nutrients are available in different lakes in Greenland, how they are produced and how they are transferred to fish through the food web. To understand the influence of glaciers on the newly formed ecosystems, the researchers investigated how fish – arctic char in particular – can meet their requirements for organic nutrients in different lake environments. They compared fish from lakes at different stages of succession: very young lakes that are still connected to glaciers, lakes that were recently disconnected from glaciers, and lakes that have been disconnected from glaciers thousands of years ago.
They found that fish in young lakes have very limited access to these nutrients compared to established ecosystems in older lakes and need to compensate by producing increased amounts themselves. However, the situation changes drastically when those lakes are linked to nearby fjords. The fish then obtain the essential nutrients from marine food sources, by feeding on the eggs of migratory char, that spend part of their lives in the fjord and transfer marine nutrients into lakes. This way, fish in the lake significantly increase their access to essential organic nutrients and even exhibited the highest concentrations of omega-3 fatty acids measured in the study. The availability of essential nutrients therefore depends not only on the age of a lake, but also on its connections to surrounding ecosystems.
Surrounding ecosystems shape new glacial lakes
These findings reveal that newly formed glacial lakes are not isolated ecosystems but are shaped by the exchange of nutrients with their surroundings from the very beginning. Through this interconnectedness, glacier retreat influences not only how much nutrition is available to animals, but also where these nutrients originate and how they move through food webs. “This finding also echoes some of our previous work, showing that glacial meltwater affects downstream ecosystems, including rivers and fjords,” says Grégoire Saboret, who completed his PhD at Eawag's Surface Water Department and currently works as Postdoctoral researcher at UCSC California. “It suggests that the impact of glacier retreat extends beyond the creation of new habitats. Because ecosystems are connected, for example through animal migrations, changes in glacier dynamics can have cascading effects across the wider landscape.”
Impressions from Greenland’s glacial landscapes, the research team and marine life. (Photos: Coralie Moccetti [1;3;4], Grégoire Saboret [2], Elliot Lewis [5;7;8] and Freya Sermilik [6])
As glaciers retreat, new questions emerge
Retreating glaciers are also rapidly transforming Switzerland’s Alpine landscapes. A comprehensive inventory of all Swiss glacial lakes from 2021 showed that almost 1,200 new glacial lakes have formed since the end of the Little Ice Age, and their number continues to grow as glaciers melt. These lakes are attracting increasing attention, not only because they create new habitats, but also because they offer opportunities for tourism, water storage and hydropower. “Glacial lakes should not be viewed as isolated ecosystems, but as ecosystems connected to the surrounding landscapes. Understanding these connections is likely to be important as glacier retreat continues and potential exploitation comes into play,” says Jakob Brodersen from Eawag’s Department Fish Ecology and Evolution.
Methodology
In this study, Eawag researchers set out to answer two key questions: Which organisms are the primary source of essential organic nutrients in newly formed glacial lakes? And how do fish obtain these nutrients? To determine the source of essential nutrients and their transfer in newly formed glacial lakes, Eawag researchers used a highly complex combination of analyses of long-chain polyunsaturated fatty acids and compound-specific isotope analysis of amino acids in muscle tissue of arctic char.
To accurately determine the food source, this method breaks down proteins into their individual components and analyses the amino acids one by one. This provides an isotope value for each amino acid, rather than an average value. Different amino acids behave differently within a food web; some become isotopically enriched at every step in the food chain, while others remain almost unchanged. This allows researchers to determine the source of these valuable amino acids, making the method particularly valuable for use in newly formed ecosystems.
This study also utilised fatty acid analysis. This method examines which fatty acids are present in a sample and in what quantities. Since many animals cannot produce some essential fatty acids themselves, or can do so only to a limited extent, they obtain them through their diet. The fatty acid profile therefore provides important clues as to what the animal has eaten.
Photo de couverture: Grégoire Saboret, catching fish in a glacial river in Greenland. (Photo: Coralie Moccetti)
