The boundless carbon cycle
Tom J. Battin, Sebastiaan Luyssaert, Louis A. Kaplan, Anthony K. Aufdenkampe, Andreas Richter and Lars J. Tranvik The terrestrial biosphere is assumed to take up most of the carbon on land. However, it is becoming clear that inland waters process large amounts of organic carbon and must be considered in strategies to mitigate climate change.
tmospheric carbon dioxide concentrations increased from ~280 ppm before the industrial revolution to over 384 ppm in 2008 (ref. 1). This increase reflects only about half of the CO2 emissions from human activities; the other half has been sequestered in the oceans and on land2,3 (Box 1). Although the location and magnitude of continental carbon sinks remain uncertain4, they are assumed to lie within the terrestrial biosphere. We argue that inland waters have a significant role in the sequestration, transport and mineralization of organic
Box 1 | Balancing the carbon cycle
carbon. Integration of these fluxes into the traditional carbon cycle is needed for appropriate CO2 management and climate change mitigation. Inland waters — such as ponds, lakes, wetlands, streams, rivers and reservoirs — permeate terrestrial ecosystems and often shape the Earth’s landscapes. Although only about 1% of the Earth’s surface is assumed to be covered by inland waters, their collective contribution to global carbon fluxes is substantial compared with terrestrial and marine ecosystems5–10. Specifically, current estimates
carbon dioxide sinks Since 1750, continuously increasing anthropogenic CO2 emissions and land-use change have perturbed the natural carbon cycle. Of the 9.1 Pg C yr–1 (1 Pg C = 1 petagram or 109 metric tons of carbon) emitted in this way between 2000 and 2006, 4.1 Pg C yr–1 have accumulated in the atmosphere, 2.2 Pg C yr–1 have been assigned to marine sequestration and the residual 2.8 Pg C yr–1 have been assigned to sequestration within the terrestrial biosphere3. At regional