Melting glaciers could speed up carbon emissions into the atmosphere, a new study suggests.
The loss of glaciers worldwide enhances the breakdown of complex carbon molecules in rivers, potentially contributing further to climate change, research indicates.
Scientists say that for the first time they have linked glacier-fed mountain rivers with higher rates of plant material decomposition, a major process in the global carbon cycle.
As mountain glaciers melt, water runs into rivers downstream.
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.
According to the research led by the University of Leeds, these conditions are much more favourable for fungi to establish and grow.
The fungi living in these rivers decompose organic matter such as plant leaves and wood, eventually leading to the release of carbon dioxide into the air.
This process has been measured in 57 rivers in six mountain ranges across the world, in Austria, Ecuador, France, New Zealand, Norway and the United States.
Lead author Sarah Fell, of Leeds’ School of Geography and water@leeds, said similar patterns and processes were discovered worldwide.
She explained: “We found increases in the rate of organic matter decomposition in mountain rivers, which can then be expected to lead to more carbon release to the atmosphere.
“This is an unexpected form of climate feedback, whereby warming drives glacier loss, which in turn rapidly recycles carbon in rivers before it is returned to the atmosphere.”
Researchers used artists’ canvas fabric to mimic plant materials such as leaves and grass that accumulate naturally in rivers.
The canvas strips were left in the rivers for approximately one month, then retrieved and tested to determine how easily they could be ripped.
According to the study published in Nature Climate Change, the strips ripped more easily as aquatic fungi colonised them, indicating that decomposition of the carbon molecules was quicker in rivers which were warmer because they had less water flowing from glaciers.
The study’s co-author, Professor Lee Brown, also of Leeds’ School of Geography, said: “Our finding of similar patterns of cellulose breakdown at sites all around the world is really exciting because it suggests that there might be a universal rule for how these river ecosystems will develop as mountains continue to lose ice.
“If so, we will be in a much improved position to make forecasts about how river ecosystems will change in future.”
