NEW RESEARCH SUGGESTS THAT HUMAN ACTIVITY could be increasing the movement of carbon from land to rivers, estuaries and the coastal zone, indicating that large quantities of anthropogenic carbon may be hidden in regions not previously considered, according to a study recently published in Nature Geoscience.When carbon is emitted by human activities into the atmosphere, it is generally thought that about half remains in the atmosphere and the remainder is stored in the oceans and on land. The study by Dr. Fred Mackenzie, emeritus professor of Oceanography at the University of Hawai`i at Manoa School of Ocean and Earth Science and Technology, and colleagues from the Université Libre de Bruxelles, the University of Exeter, Laboratoire des Sciences du Climat et l’Environnement and ETH Zurich showed, for the first time, that increased leaching of carbon from soil, mainly due to deforestation, sewage inputs and increased weathering, has resulted in less carbon being stored on land and more stored in rivers, streams, lakes, reservoirs, estuaries and coastal zones – environments that are together known as the land-ocean aquatic continuum. The study reviewed previously published data and showed that a significant amount of the carbon emitted through human activity that is taken up by the land is not actually stored there, but in the aquatic continuum. Pierre Regnier, from Université Libre de Bruxelles, said, “The budget of anthropogenic CO2 reported by the Intergovernmental Panel on Climate Change currently does not take into account the carbon leaking from terrestrial ecosystems to rivers, estuaries and coastal regions. As a result of this leakage, the actual storage by terrestrial ecosystems is about 40 percent lower than the current estimates by the IPCC.” The land-ocean aquatic continuum has not previously been considered an important carbon sink. Future assessments of carbon storage must now take into account the surface areas of the land-ocean aquatic continuum to ensure accurate estimation of carbon storage. This will also require an improved knowledge of the mechanisms controlling the degradation, preservation and emissions of carbon along the aquatic continuum to fully understand the impact of human activity on carbon transfer. Professor Pierre Friedlingstein, from the University of Exeter, said, “Carbon storage in sediments in these rivers and coastal regions could present a more secure environment than carbon stored in soil on land. As soil warms up, stored carbon can be lost to the atmosphere. The chances of this occurring in wet sediments are reduced.” A fraction of the carbon that leaches from land to the land-ocean aquatic continuum is emitted back to the atmosphere, while another fraction is sequestered in sediments along the continuum. Only a minor part, about 10 percent, eventually reaches the open ocean. Philippe Ciais, from the Laboratoire des Sciences du Climat et l’Environnement, said, “Our revisited global carbon budget, which includes the land-ocean aquatic continuum, is still entailed with significant uncertainties. It is, however, fully consistent with the observed growth rate of atmospheric CO2. Our downward revision of the land carbon storage is also in agreement with very recent results from forest inventories.” A significant part of the carbon storage thought to be offered by ecosystems on land – mainly forests – is thus negated by this leakage of carbon from soils to aquatic systems, and to the atmosphere, according to the study. For more information, see the article at dx.doi.org/10.1038/NGEO1830.
Posted on: Sun, 16 Jun 2013 03:34:55 +0000
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