Tidal Inundation Decreases Carbon Dioxide Exchange in an Irish Atlantic Saltmarsh

Abstract

Despite the growing interest in carbon cycling in tidal‐wetland ecosystems we lack sufficient understanding of the degree to which saltmarsh ecosystems sequester carbon and the ecosystem dynamics of carbon dioxide (CO ₂ ) exchange, especially with tidal influence. The eddy covariance method was used to estimate a carbon budget at the ecosystem‐scale for an Irish Atlantic saltmarsh and investigate the effects of tidal inundation on net ecosystem exchange (NEE). NEE was partitioned into gross primary productivity (GPP) and ecosystem respiration (R _eco ). Biophysical drivers were determined on hourly, diurnal, and multiday timescales using wavelet analysis. Growing season R _eco and GPP during spring‐ and neap‐tide periods were also investigated to assess tidal impacts on CO ₂ flux magnitude. Derrymore saltmarsh acted as a CO ₂ sink for all but 4 months of the year, sequestering 307 g C m ⁻²  yr ⁻¹ . Biophysical drivers of CO ₂ fluxes scaled temporally: hourly NEE and GPP were primarily regulated by latent energy ( E ), diurnal variations responded to both E and photosynthetically active radiation (PAR). On multiday scales, however, PAR emerged as the dominant driver. Similarly, while air temperature ( T _a ) governed R _eco at hourly and diurnal frequencies, multiday respiration was shaped by the combined influence of T _a , water temperature, and water level ( H _w ). Marsh full inundation ( H _w  > 0 m) by tidal waters decreased daytime GPP up to 73%, and night‐time R _eco up to 45% during the growing season. This research shows that even in northern climates, saltmarshes can be productive and valuable carbon sinks, though their performance is strongly affected by tidal flooding.