Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/bg-2017-90
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
12 Apr 2017
Review status
This discussion paper is under review for the journal Biogeosciences (BG).
Hydrological and ecological controls on dissolved carbon concentrations in groundwater and carbon export to surface waters in a temperate pine forest watershed
Loris Deirmendjian1, Denis Loustau2, Laurent Augusto2, Sébastien Lafont2, Christophe Chipeaux2, Dominique Poirier1, and Gwenaël Abril1,3,a 1Laboratoire Environnements et Paléoenvironnements Océaniques et Continentaux (EPOC), CNRS, Université de Bordeaux, Allée Geoffroy Saint-Hilaire, 33615 Pessac Cedex, France
2INRA, UMR 1391 Interactions Sol-Plante-Atmosphère (ISPA), 33140 Villenave d'Ornon, France
3Departamento de Geoquímica, Universidade Federal Fluminense, Outeiro São João Batista s/n, 24020015, Niterói, RJ, Brazil
aalso at: Laboratoire d'Océanographie et du Climat, Expérimentations et Approches Numériques (LOCEAN), Centre IRD France-Nord, 32, Avenue Henri Varagnat, 93143 Bondy, France
Abstract. Export of soil carbon to superficial water through the drainage of groundwater is a significant but poorly documented component of the continental carbon budget. We monitored the concentrations of dissolved organic and inorganic carbon (DOC and DIC) in groundwaters and first order streams of a small temperate, forested and sandy watershed where hydrology occurs exclusively through drainage (no surface runoff). The studied watershed was also implemented for continuous measurements of groundwater table, precipitation, evapotranspiration, river discharge, and net ecosystem exchanges of sensible and latent heat fluxes as well as CO2. On a monthly basis, we found a good consistency between precipitation and the sum of evapotranspiration, drainage and groundwater storage. DOC and DIC temporary storage in groundwater and export to streams varied drastically during the hydrological cycle, the residence times of these two carbon forms varying from one month to several years. DOC concentrations in groundwater and streams were maximal at high water table and high stream discharge, when the water table reached the superficial organic rich layer of the soil. A large fraction of this winter DOC maximum was temporarily stored and further mineralized to DIC in the groundwater and only about 15 % was exported to streams during winter periods. In contrast, DIC, which was present in majority in the form of dissolved CO2 in groundwater and streams, was apparently diluted at high water table: DIC concentrations were maximum at low water table and low discharge in late summer and maximum pCO2 in groundwater corresponded to the late summer period of heterotrophic conditions (i.e., Reco > GPP). Groundwater DIC peaked in late summer and was followed by a rapid loss of excess CO2 from stream surface to the atmosphere. Overall, mean carbon export was 7.5 g C m−2 yr−1 (50 % as DOC and 50 % as DIC) and represented only 1.5 % of the NEE. About 65 % of the DIC exported from groundwaters returned to the atmosphere in the form of CO2 in first order streams.

Citation: Deirmendjian, L., Loustau, D., Augusto, L., Lafont, S., Chipeaux, C., Poirier, D., and Abril, G.: Hydrological and ecological controls on dissolved carbon concentrations in groundwater and carbon export to surface waters in a temperate pine forest watershed, Biogeosciences Discuss., doi:10.5194/bg-2017-90, in review, 2017.
Loris Deirmendjian et al.
Loris Deirmendjian et al.
Loris Deirmendjian et al.

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Short summary
Some authors have recently highlighted that export of terrestrial carbon from soil and groundwaters to inland waters could represent 50–100 % of the net forest productivity. Here, we demonstrated that at least in sandy lowland areas, this number seems overestimated. Indeed, we found that export of carbon through soil and groundwater represents only 1.5 % of the net forest productivity. This result puts doubts on the global estimation of terrestrial carbon export from soil to inland waters
Some authors have recently highlighted that export of terrestrial carbon from soil and...
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