Thursday, September 23

Glacier loss increases the breakdown of complex carbon molecules in rivers


The Perito Moreno glacier in Argentina

The Perito Moreno glacier in Argentina
ShutterStock

An international research team led by the University of Leeds in the United Kingdom has for the first time linked glacier-fed mountain rivers with higher rates of decomposition of plant material, an important process in the global carbon cycle. As mountain glaciers melt, the water is channeled into rivers. But with global warming accelerating the loss of glaciers, rivers have warmer water temperatures and are less prone to variable water flow and sediment movement. These conditions are much more favorable for fungi to establish and grow.

The fungi that live in these rivers break down organic matter, such as plant leaves and wood, eventually leading to the release of carbon dioxide into the air. The process, a key part of the global river carbon cycle, has now been measured in 57 rivers in six mountain ranges around the world, in Austria, Ecuador, France, New Zealand, Norway and the United States.

Sarah Fell, from the Leeds and Water Leeds School of Geography, and lead author of the study, published in the journal Nature Climate Change, explains that similar patterns and processes have been discovered around the world. “We found increases in the rate of decomposition of organic matter in mountain rivers, which can then be expected to lead to a greater release of carbon into the atmosphere,” he adds.

“This is an unexpected form of climate feedback, whereby warming causes the loss of glaciers, which in turn rapidly recycle carbon in rivers before it returns to the atmosphere,” he continues.

The retreat of mountain glaciers is accelerating at an unprecedented rate in many parts of the world, and climate change is projected to cause continued ice loss during the 21st century. However, the response of river ecosystem processes (such as nutrient and carbon cycling) to shrinking glacier cover, and the role of fungal biodiversity in driving them, remains poorly understood.

The research team used artists’ canvas fabric to mimic plant materials such as leaves and grass that naturally accumulate in rivers. This was possible because the canvas is made of cotton, predominantly composed of a compound called cellulose, the world’s most abundant organic polymer found in plant leaves that naturally accumulate in rivers.

The canvas strips were left in the rivers for about a month, then recovered and tested to determine how easily they could tear. The stripes tore more easily as aquatic fungi colonized them, showing that the breakdown of carbon molecules occurred more rapidly in rivers that were warmer because they had less water flowing from glaciers.

Study co-author Professor Lee Brown, also from the Leeds School of Geography explains: “Our finding of similar patterns of cellulose degradation at sites around the world is really exciting because it suggests that there might be a universal rule on how these river ecosystems will develop as mountains continue to lose ice. If so, we will be in a much better position to forecast how river ecosystems will change in the future, “he says.

Co-author Professor Alex Dumbrell, whose team at the University of Essex analyzed fungi in river samples, adds that the work “showed that measuring a specific gene that supports the activity of the cellulose-degrading enzyme (Cellobiohydrolase I) meant that We could better predict the decay of cotton strips than using information on the abundance of the fungal species themselves, which is the most commonly used approach. This opens up new avenues for research to improve our predictions of changes in the carbon cycle. “, get moving.

Since the growth of algae and plants in glacier-fed rivers is minimized by low water temperatures, unstable channels, and high levels of fine sediment, decomposition of plant matter can be an important source of fuel for these aquatic ecosystems. In some parts of the world, such as Alaska and New Zealand, glacier-fed rivers also extend into forests that provide greater amounts of litter to river food chains.

Furthermore, because the loss of glaciers means that less water flows through rivers and they are less likely to change course, plants and trees along the banks are expected to grow more in these habitats in the future, which it means that even more litter will accumulate in the rivers. This is likely to accelerate the fungal processing of carbon in mountain rivers around the world even more than today, the authors note.


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