A lake classification concept for a more accurate global estimate of the dissolved inorganic carbon export from terrestrial ecosystems to inland waters

English. Funding information. Financial support was received from the SwedishResearch Council (Grant No. 2016-04153), the European Union’sHorizon 2020 research and innovation program under the MarieSklodowska-Curie grant agreement No 643052 (C-CASCADES project),and from the Knut and Alice Wallenberg Foundation (KAW project). Thiswork profited from the Global Lake Ecological Observatory Network(GLEON). The Estonian partners were supported by institutional researchfunding IUT 21-02 of the Estonian Ministry of Education and Research,and American partners were supported, in part, through NSF EF-1137327.

English. The magnitude of lateral dissolved inorganic carbon (DIC) export from terrestrial ecosystems to inland waters strongly influencesthe estimate of the global terrestrial carbon dioxide (CO2) sink. At present, no reliable number of this export is available, and thefew studies estimating the lateral DIC export assume that all lakes on Earth function similarly. However, lakes can function alonga continuum from passive carbon transporters (passive open channels) to highly active carbon transformers with efficient in-lakeCO2 production and loss. We developed and applied a conceptual model to demonstrate how the assumed function of lakes incarbon cycling can affect calculations of the global lateral DIC export from terrestrial ecosystems to inland waters. Using globaldata on in-lake CO2 production by mineralization as well as CO2 loss by emission, primary production, and carbonate precip-itation in lakes, we estimated that the global lateral DIC export can lie within the range of 0:70þ0:27−0:31 to 1:52þ1:09−0:90 Pg C yr−1depending on the assumed function of lakes. Thus, the considered lake function has a large effect on the calculated lateral DICexport from terrestrial ecosystems to inland waters. We conclude that more robust estimates of CO2 sinks and sources will requirethe classification of lakes into their predominant function. This functional lake classification concept becomes particularlyimportant for the estimation of future CO2 sinks and sources, since in-lake carbon transformation is predicted to be altered withclimate change.