As human activities continue to pump carbon into the atmosphere, the backbone of our understanding of the resulting warming is our knowledge of where that carbon is going: into the atmosphere, into the land, and into bodies of water. When it comes to accounting for the carbon absorbed and emitted by water, the role of inland freshwater may appear quite small compared to the vastness of Earth’s oceans. After all, inland lakes, rivers, streams, reservoirs, wetlands, and estuaries cover less than 4% of Earth’s surface [Downing, 2010; Verpoorter et al., 2014].But recent research shows that the roughly 200 million bodies of inland water play a much larger role in the global carbon cycle than their small footprint suggests. Inland streams and rivers move vast amounts of carbon from the land to the ocean, acting as carbon’s busy transit system.
They also play a disproportionately large role in the global carbon cycle through their high rates of carbon respiration and sequestration [Cole et al., 2007; Tranvik et al., 2009].According to recent estimates, the amount of carbon that inland waters emit is comparable to the net amount of carbon absorbed by living organisms on Earth’s land surface and in its oceans. Moreover, bodies of freshwater bury more carbon in sediments each year than the vast ocean floor [Battin et al., 2009; Aufdenkampe et al., 2011].
Nevertheless, there is great uncertainty in these figures, and scant data exist on continental and global scales. The changing climate is putting freshwater ecosystems at great risk: They are warming at an alarming rate, outpacing warming of the atmosphere and oceans. It’s crucial that scientists dedicate more resources to understanding the global impact of the freshwater continuum on the carbon cycle.
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