Hydrology

Lake carbon

Credit: © ISTOCKPHOTO/MELASTMOHICAN

Inland waters, such as lakes, reservoirs, wetlands and rivers, occupy only a small fraction of the Earths' surface, but have a disproportionate effect on the global carbon cycle. These land-based water bodies bury, cycle and emit significant sums of carbon. A large amount of the carbon taken up by terrestrial systems ends up in inland waters, where it can be buried in sediments, transported to the oceans, or mineralized and released back into the atmosphere as carbon dioxide.

Despite the climatic implications, little is known about the factors that regulate the balance between carbon burial and release in inland waters. Without this knowledge, it is difficult to determine the influence of climate change on lake carbon content, and ultimately carbon release.

Sarian Kosten, of Wageningen University, The Netherlands, and colleagues show that warm lakes contain more carbon dioxide than cool lakes (Glob. Biogeochem. Cycles doi:10.1029/2009GB003618; in the press). The researchers examined carbon dioxide concentrations in 82 shallow lakes in South America. The lakes spanned a large temperature gradient; annual mean temperature ranged from 4 °C in the south, to 27 °C in the north. 80% of the lakes sampled contained higher concentrations of carbon dioxide than the atmosphere, indicating that they functioned as net sources of carbon dioxide. A regression analysis revealed that lake carbon dioxide concentrations increased with lake temperature. As expected, hydrology and primary productivity also explained a considerable part of the variance in lake carbon dioxide concentrations.

The authors suggest that the higher carbon dioxide concentrations in the warmer lakes can be explained by higher rates of respiration. Warm lakes might metabolize a greater proportion of the terrestrial organic carbon entering the water than cool lakes, leading to increased levels of carbon dioxide.

Because carbon dioxide concentrations in lakes have been found to be closely linked to carbon dioxide emissions from these water bodies, the researchers suggest that lakes in a warmer environment emit more of the greenhouse gas.

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Armstrong, A. Lake carbon. Nature Geosci 3, 151 (2010). https://doi.org/10.1038/ngeo816

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