How climate change affects the decomposition of organic material

On the way to the oceans, microorganisms decompose parts of the organic material transported from the land ecosystems. It is crucial to know what controls the speed of this process for our understanding of how the turnover of organic materials is affected by environmental changes. A study by researchers at Uppsala University and the Swedish Agricultural University (SLU) has shown how the degradation is controlled by the environment on a large scale, especially by the water balance.

Large amounts of organic matter are transported from the land ecosystems, through the world's lakes and rivers, down to the oceans. Only a portion of it makes it all the way to the sea, the rest is lost on the way, largely by degradation by microorganisms in the water.

The wetter the climate is, the faster water in the landscape is flushed through lakes and rivers, towards the sea. The time water is retained in the land ecosystems thus becomes shorter, and there will be less time for microorganisms to degrade various organic substances in the water.

To investigate how this affects how fast the organic matter is degraded, researchers from Uppsala University, SLU, and Girona in Spain have compiled data from over three hundred published studies, where the degradation rate was measured at various renewal times of water. The researchers found that the organic material degrades faster when at faster water turnover. They then compared the correlation they found between water circulation and decay, with scenarios for expected changes in water turnover due to climate changes. Some areas will become wetter with more rapid runoff of water; others will become drier. Thus, the degradation will be faster in many northern areas, but slower in for example the Mediterranean.

The researchers found, among other things, that the average half-life of organic matter in lakes and rivers is two and a half years. This is significantly shorter than in most other environments, such as soils, oceans and sediments. Inland waters can be regarded as a bit of a global "hot spot" for the breakdown of organic material.

The research is a collaboration with SLU, a Spanish research institutes, and was financed by Formas, the Knut and Alice Wallenberg Foundation, and a grant from the Wenner-Gren Foundations to Núria Catalan, who is the first author of the article.

The findings are published in the journal Nature Geoscience.
Reference: Catalan, N., Marcé, R., Kothawala, D. N., and Tranvik, L. J. Organic carbon decomposition rates controlled by water retention time across the inland waters. Nature Geoscience.