Carbon dioxide fluxes increase from day to night across European streams

Abstract

Globally, inland waters emit over 2 Pg of carbon per year as carbon dioxide, of which the majority originates from streams and rivers. Despite the global significance of fluvial carbon dioxide emissions, little is known about their diel dynamics. Here we present a large-scale assessment of day- and night-time carbon dioxide fluxes at the water-air interface across 34 European streams. We directly measured fluxes four times between October 2016 and July 2017 using drifting chambers. Median fluxes are 1.4 and 2.1 mmol m−2 h−1 at midday and midnight, respectively, with night fluxes exceeding those during the day by 39%. We attribute diel carbon dioxide flux variability mainly to changes in the water partial pressure of carbon dioxide. However, no consistent drivers could be identified across sites. Our findings highlight widespread day-night changes in fluvial carbon dioxide fluxes and suggest that the time of day greatly influences measured carbon dioxide fluxes across European streams

We thank the initiators of the first Collaborative European Freshwater Science Project for Young Researchers, the European Federation of Freshwater Sciences (EFFS) board, the European Fresh and Young Researchers (EFYR) and the representatives of the Fresh Blood for Fresh Water (FBFW) meetings. We also thank the seven national freshwater societies financing this project, namely the Iberian Association of Limnology (AIL; Spain and Portugal), Deutsche Gesellschaft für Limnologie e.V. (DGL; Germany), Swiss Society for Hydrology and Limnology (SGHL; Switzerland), Italian Association of Oceanography and Limnology (Italy), Freshwater Biological Association (FBA; United Kingdom), French Limnological Association (AFL; France), Austrian Limnological Society (SIL-Austria), as well as the Leibniz-Institute of Freshwater Ecology and Inland Fisheries for additional funds. Additional funding was awarded to J.P.C.-R. by a Juan de la Cierva postdoctoral grant from the Spanish Government (FJC2018-037791-I), to A.P.P. by a Ph.D. grant from the Fundação para a Ciência e Tecnologia (SFRH/BD/115030/2016), to B.C.D. by the Marine Institute’s Cullen Ph.D. fellowship (Grant No. CF/15/05), to N.C. by the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement (No. 839709), to J.M. by FCT (Portuguese Science Foundation) through a Ph.D. grant (SFRH/BD/131924/2017), to J.P. by the DSI/NRF Research Chair in Inland Fisheries and Freshwater Ecology, to A.F. by the Juan de la Cierva postdoctoral grant from the Spanish Government (FJCI-2017–33171), and to C.M.-L. by the French National Agency for Water and Aquatic Environments (ONEMA, Action 13, “Colmatage, échanges nappe-rivière et processus biogéochimiques”). Open access funding provided by University of Vienna

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