The role of groundwater in CO 2 production and carbon storage in Mediterranean peatlands: An isotope geochemistry approach

• Published in: The Science of the total environment Vol. 866; p. 161098
• Main Authors: Santoni, S, Garel, E, Gillon, M, Babic, M, Spangenberg, J E, Bomou, B, Sebag, D, Adatte, T, van Geldern, R, Pasqualini, V, Mattei, A, Huneau, F
• Format: Journal Article
• Language: English
• Published: Netherlands 25-03-2023
• Subjects: Peatland‑carbon-water system; Origin of carbon; Sources and sinks of carbon; Peatland-atmosphere interface; Groundwater-dependent ecosystem
• ISSN: 1879-1026

Peatlands are permanent wetlands recognized for ecosystem services such as biodiversity conservation and carbon storage capacity. Little information is available about their response to global change, the reason why most Earth system climate models consider a linear increase in the release of greenhouse gases (GHG), such as CO
, with increasing temperatures. Nevertheless, numerous studies suggest that an increase in the temperature may not imply a decrease in photosynthesis and carbon storage rates if water availability is sufficient, the latter being under the control of local hydrology mechanisms. Mediterranean peatlands well illustrate this fact. Since they are groundwater-dependent, they are hydrologically resilient to the strong seasonality of hydroclimatic conditions, especially during the summer drought. In the present study, we demonstrate that, even if such peatlands release CO
into the atmosphere, they can maintain a carbon storage capacity. To this end, a geochemical study disentangles the origin and fate of carbon within a Mediterranean peatland at the watershed scale. Field parameters, major ions, dissolved organic and inorganic carbon content and associated δ
C values allow for characterizing the seasonality of hydrochemical mechanisms and carbon input from an alluvial aquifer (where rain, river, shallow, and deep groundwater flows are mixing) to the peatland. The inorganic and organic content of peat soil and δ
C values of total organic matter and CO
complete the dataset, making it possible to provide arguments in favour of lower organic matter oxidation compared to primary production. Overall, this study highlights the groundwater role in the fluxes of CO
at the peatland-atmosphere interface, and more broadly the need to understand the interactions between the water and carbon cycles to build better models of the future evolution of the global climate.