Lakes an important source of carbon emissions



Around the world, vast detector networks track the transfer of carbon as it flows through the ecosystem, moving among the atmosphere, terrestrial surface, and organic matter. These carbon flux measurements are integral to understanding the role of various ecosystem components in the global carbon cycle and to performing accurate carbon accounting. But when precipitation or other processes pull large volumes of organic matter from the land into nearby lakes, this carbon effectively disappears from the carbon budget if gas fluxes over the lake surface are ignored, which they traditionally have been. Using eddy covariance measurements, Huotari et al. tracked the flow of carbon into and out of Lake Valkea-Kotinen in southern Finland from the spring of 2003 until the autumn of 2007. They found that the lake was a net source of carbon, emitting between 70 and 100 grams of carbon per square meter per year. When compared against the role of the surrounding forest, which was a net carbon sink, the lake's emissions were enough to offset about 10% of the forest's annual carbon storage. The authors found that the strongest controlling factor on the lake carbon emission rate was the stability of the lake's temperature stratification. Strong winds, heavy precipitation, and seasonal changes that increase water mixing were linked to stronger carbon fluxes. (Geophysical Research Letters, doi:10.1029/2011GL048753, 2011)