When glaciers melt, carbon rises

In the face of rising temperatures, water from glaciers may be both a bane and a boon for rivers, as the melting contributes to the carbon cycle.

An international team, led by Sarah Fell of the University of Leads, UK, has found that mountain rivers that rely on mountain glacier water have higher rates of plant decomposition, which, in turn, leads to more carbon in the atmosphere.

Key research points

  • More warmer water from melting temperatures enters mountain rivers.
  • Extra water allows fungi to grow.
  • More fungi lead to higher plant matter decomposition.
  • Decomposition releases carbon dioxide.

Ordinarily, the fresh water that comes from mountain glaciers feeds rivers and contributes to the flow of water that helps river plants and fungi grow. When warmer temperatures cause the glaciers to melt faster, more warmer water flows into the rivers and disrupts the normally variable nature of the riverbed.

Fuelled by these increased flows of warmer water, the fungi that love to grow in rivers bloom excessively.

These fungi decompose other plant matter than falls into the river, such as wood and leaves. Decomposition releases carbon dioxide, so the more warmer water that comes into the river, the more fungi there is to decompose plant material, and more carbon ends up back in the air in a big feedback loop.

“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,” says Fell.

“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.”

In their paper, published in Nature Climate Change, the team show this process in 57 rivers in six major mountain ranges, including ranges in New Zealand, Austria, France, Norway and the US.

“Our finding of similar patterns of cellulose [a plant component] 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,” says Alex Drumbrell, of the University of Essex.

“If so, we will be in much improved position to make forecasts about how river ecosystems will change in future.”

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