Coastal environments such as the Charentais Sounds are key systems in the biogeochemical cycles coupling (C, N, P) between the land, the ocean and  the atmosphere. Within the coastal zone, salt marshes are considered as CO₂ sinks associated to their significant autotrophic metabolism and sediment carbon (C) storage. However, this ecological functioning is more and more threatened by global change (acidification, sea level rise, eutrophication) and anthropogenic pressures decreasing blue C area potential worldwide. C dynamics over salt marshes are complex since various processes and fluxes take place at the different terrestrial-aquatic-atmospheric exchange interfaces at the spatio-temporal scales of the coastal zone. The ANR-PAMPAS research project allows a better understanding of marsh ecological functioning located in the Charentais Sounds according to their typology and management practices faced oceanic submersion risks. Related to the blue C sink ecological functioning, this internship specifically focused on the dynamic of water partial pressures of CO₂ (pCO₂) and associated relevant environmental parameters at diurnal, tidal and seasonal scales along a dyked salt marsh – channel – bay continuum within the Fier d’Ars coastal wetland (Ré Island). The diurnal/tidal measurements carried out from year 2018 to 2020 at stations along the continuum highlighted a strong biological control on water pCO₂ and associated metabolisms at diurnal and seasonal scales according to station typology and management practices too. During spring-summer seasons at dyked salt marsh stations, photosynthesis activity of macroalgae, seagrass and phytoplankton produced large CO₂ undersaturation. To the contrary during winter-autumn seasons, lower biological activity associated with microbial loop-type network particularly at channel water station induced large CO₂ oversaturation with regards to the atmosphere. Other non-temperature effect such as coastal water advection significantly influenced diurnal water CO₂ dynamics among connected stations. Over the year, the majority of the studied stations (bay and dyked marshes) behaved as CO₂ sinks (-0.03 ± 0.17 and -0.26 ± 0.38 mmol m² h^-1 at Fier d’Ars Bay and Loix marsh respectively) while only the channel station connecting coastal waters of the bay to dyked marshes represented a CO₂ source to the atmosphere (+0.16 ± 0.24 mmol m² h^-1).