"There is a substantial amount of plant litter that accumulates in dry riverbeds and when they flow again this material can break down rapidly. We've now estimated the potential short-term CO2 emissions during these rewetting events," said Nathan Waltham from James Cook University in Australia.
"We believe that a single pulse of CO2 emission upon litter rewetting contributes up to 10 per cent of the daily CO2 emission compared to perennial rivers and streams, particularly in temperate climates.
"What this means is that the contributions of intermittent rivers and streams should be included in global carbon-cycling assessments," Waltham added.
Intermittent rivers, as the name suggests, sometimes stop flowing and can dry completely. Although far less studied than permanent rivers, they could represent half of the world's river network and, in response to climate change and increasing water demands, may come to dominate the landscape in some regions.
For the study, the international team of researchers looked at 212 dry riverbeds in the world.
The results published in the journal Nature Geoscience showed that aridity, surrounding vegetation, channel width and dry-phase duration explained most variability in the quantity and decomposability of plant litter.
"Taking rivers and streams that only flow at certain times into account would improve estimates of the consequences of global climate change on carbon cycling -- given that the extent of these rivers and streams will increase, and periods of drying will become more prolonged in many regions," Waltham said.
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