CARBON-DIOXIDE SUPERSATURATION IN THE SURFACE WATERS OF LAKES

Data on the partial pressure of carbon dioxide (CO2) in the surface wa ters from a large number of lakes (1835) with a worldwide distribution show that only a small proportion of the 4665 samples analyzed (less than 10 percent) were within +/-20 percent of equilibrium with the atm osphere and that most samples (87 percent) were supersaturated. The me an partial pressure of CO2 averaged 1036 microatmospheres, about three times the value in the overlying atmosphere, indicating that lakes ar e sources rather than sinks of atmospheric CO2. On a global scale, the potential efflux of CO2 from lakes (about 0.14 x 10(15) grams of carb on per year) is about half as large as riverine transport of organic p lus inorganic carbon to the ocean. Lakes are a small but potentially i mportant conduit for carbon from terrestrial sources to the atmospheri c sink.