Background
The authors write that "lakes transport, transform, and store considerable quantities of carbon in inland aquatic ecosystems (Cole et al., 2007)." And they say that "although lakes cover a small fraction of Earth's continental land areas, organic carbon burial in lake sediments is considerably higher than in ocean sediments (Dean and Gorham, 1998; Downing et al., 2008; Battin et al., 2009), and are comparable to that in soils (Gudasz et al., 2010."

What was done
Working at Lake Qinghai "in the arid/semi-arid region of the northeastern Qinghai-Tibet plateau, where the Asian summer monsoon, westerly jet stream, and Asian winter monsoon converge," Xu et al. estimated modern carbon burial, "as well as the carbon influxes from different origins and discuss their possible linkages to climatic changes."

What was learned
The major findings of the group of five researchers were that (1) "the organic carbon burial rate in sediments of Lake Qinghai is similar to those in large lakes worldwide," that (2) "organic carbon in lake sediments is mainly deposited from particulate organic carbon in lake water," of which (3) "near 80% is of terrestrial origin," that (4) "the inorganic carbon burial rate is slightly higher than that of organic carbon," that (5) "about 70% of the riverine dissolved inorganic carbon is directly/indirectly withdrawn from atmospheric CO2," that (6) "the carbon burial rate in lake sediment is higher during warm-wet periods," and, as a result, that (7) "lakes in similar regions may play an increasingly important role in global carbon cycling as global warming proceeds."

What it means
The various findings of Xu et al. illuminate yet another means by which Earth's biosphere and hydrosphere are combining forces to retard the rate-of-rise of CO2-induced global warming.

References
Battin, T.J., Luyssaert, S., Kaplan, L.A., Aufdenkampe, A.K., Richter, A. and Tranvik, L.J. 2009. The boundless carbon cycle. Nature Geoscience 2: 598-600.

Cole, J.J., Prairie, Y.T., Striegl, R.G., Caraco, N.F., Duarte, C.M., McDowell, W.H., Kortelainen, P., Middleburg, J.J., Tranvik, L.J., Downing, J.A. and Melack, J. 2007. Plumbing the global carbon cycle: integrating inland waters into the terrestrial carbon budget. Ecosystems 10: 171-184.

Dean, W.E. and Gorham, E. 1998. Magnitude and significance of carbon burial in lakes, reservoirs, and peatlands. Geology 26: 535-538.

Downing, J.A., Cole, J.J., Middelburg, J.J., Striegl, R.G., Duarte, C.M., Kortelainen, P., Prairie, Y.T. and Laube, K.A. 2008. Sediment organic carbon burial in agriculturally eutrophic impoundments over the last century. Global Biogeochemical Cycles 22: 10.1029/2006GB02854.

Gudasz, C., Bastviken, D., Steger, K., Premke, K., Sobek, S. and Tranvik, L.J. 2010. Temperature controlled organic carbon mineralization in lake sediments. Nature 466: 478-481.