20 Jul 2023
 | 20 Jul 2023

Atmospheric CO2 exchanges measured by Eddy Covariance over a temperate salt marsh and influence of environmental controlling factors

Jérémy Mayen, Pierre Polsenaere, Éric Lamaud, Marie Arnaud, Pierre Kostyrka, Jean-Marc Bonnefond, Philippe Geairon, Julien Gernigon, Romain Chassagne, Thomas Lacoue-Labarthe, Aurore Regaudie de Gioux, and Philippe Souchu

Abstract. Within the coastal zone, salt marshes are atmospheric CO2 sinks and represent an essential component of biological carbon (C) stored on Earth due to a strong primary production. Significant amounts of C are processed within these tidal systems which requires a better understanding of the temporal CO2 flux dynamics, the metabolic processes involved and the controlling factors. Within a temperate salt marsh (French Atlantic coast), continuous CO2 exchange measurements were performed by the atmospheric eddy covariance technique to assess the net ecosystem exchange (NEE) at diurnal, tidal and seasonal scales and the associated relevant biophysical drivers. During emersion, NEE fluxes were partitioned into net ecosystem production (NEP), gross primary production (GPP) and ecosystem respiration (Reco) to study marsh metabolic processes. Over the year 2020, the measured net C balance was -483 g C m-2 yr-1 while GPP and Reco absorbed and emitted 1019 and 533 g C m-2 yr-1, respectively. The highest CO2 uptake was recorded in spring during the growing season for halophyte plants in relationships with favourable environmental conditions for photosynthesis whereas in summer, higher temperatures and lower humidity rates increased ecosystem respiration. At the diurnal scale, the salt marsh was a CO2 sink during daytime, mainly driven by light, and a CO2 source during night-time, mainly driven by temperature, irrespective of emersion or immersion periods. However, daytime immersion strongly affected NEE at the daily scale by reducing marsh CO2 uptake up to 90 %. During night-time immersion, CO2 emissions could be completely suppressed, even causing a change in metabolic status from source to sink under certain situations, especially in winter when Reco rates were lowest. At the annual scale, tidal rhythm did not significantly affect the net C balance of the studied salt marsh since similar annual values of measured NEE and estimated NEP were recorded.

Jérémy Mayen et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1641', Anonymous Referee #1, 07 Aug 2023
  • RC2: 'Comment on egusphere-2023-1641', Francisco Artigas, 16 Aug 2023

Jérémy Mayen et al.

Jérémy Mayen et al.


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Short summary
We deployed an atmospheric eddy covariance system to measured continuously the net ecosystem CO2 exchanges (NEE) over a salt marsh and determine the major biophysical drivers. Our results showed an annual carbon sink mainly due to photosynthesis of the marsh plants. Our study also provides relevant information on NEE fluxes during marsh immersion by decreasing daytime CO2 uptake and night-time CO2 emissions at the daily scale whereas the immersion did not affect the annual marsh C balance.