While humans search for increasingly innovative ways to capture excess carbon dioxide from the atmosphere, the extent of our rivers’ ability to remove and store carbon is only just being understood.
Rivers transport decaying organic material and eroded rock to our oceans, playing a vital role in the global carbon cycle. Now estimates of how much carbon they flush from the land have emerged, helping experts make more accurate climate change predictions.
The Earth’s circulatory system
Scientists from the Woods Hole Oceanographic Institution (WHOI) calculated that the world’s rivers annually transport 200 megatons (200 million tons) of carbon to the ocean, equalling around .02 per cent of the total mass of carbon in the atmosphere. WHOI said: “That may not seem like a lot, but over 1000 to 10,000 years, it continues to add up to significant amounts of carbon (20 and 200 per cent) extracted from the atmosphere.”
Plants convert CO2 via photosynthesis, however much of the carbon is returned to the earth when plants decompose. At this point our rivers step in, and carry the carbon they receive from the plants out to sea, where it ends up on the sea bed, disconnected from the atmosphere for a period of millions of years. Rivers also erode rocks, and carry their carbon in particles out to the oceans.
The WHOI study has now also allowed scientists to understand how much of the carbon taken away by the rivers is from decomposed plants, and how much is from eroded rock. “Without this information, scientists’ ability to model or quantitatively predict carbon sequestration under different scenarios was limited”, the organisation said.
This has now been solved, by identifying the amount of the radioactive isotope carbon- 14 is in the river, since this is only present in living things, and not rocks. It was calculated that the amount of carbon coming from the terrestrial biosphere was about 80 per cent.
WHOI explained why these discoveries were of significance: “The new study gives scientists a firmer handle on measuring the important, and heretofore elusive, role of global rivers in the planetary carbon cycle and enhances their ability to predict how riverine carbon export may shift as earth’s climate changes.”
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PHOTO CREDIT: Sheila Sund from flickr